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Title: The Gasoline Motor


Author: Harold Whiting Slauson



Release Date: June 10, 2014  [eBook #45932]

Language: English

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THE GASOLINE MOTOR

by

HAROLD WHITING SLAUSON, M. E.

Author of "The Motor Boat"







Outing Handbooks

New York
Outing Publishing Company
MCMXIII

Copyright, 1913, by
Outing Publishing Company

All rights reserved




CONTENTS


     I. TYPES OF MOTORS              9

    II. VALVES                      24

   III. BEARINGS                    43

    IV. THE IGNITION SYSTEM         62

     V. MAGNETOS                    83

    VI. CARBURETORS AND THEIR FUEL  90

   VII. LUBRICATION                112

  VIII. COOLING                    130

    IX. TWO CYCLE MOTORS           148




THE GASOLINE MOTOR




THE GASOLINE MOTOR

CHAPTER I

TYPES OF MOTORS


There are certain events that must happen in a gasoline motor before
the engine will run of its own accord. For instance, to obtain
successive power impulses, the charge must first be admitted to the
cylinder and compressed; it must then be ignited to form the explosion
that creates the force at the flywheel; and the burned gases resulting
from this explosion must be ejected in order to clear the cylinder
for the new charge. To accomplish this series of events, some motors
require four strokes, while others do the business in two. These are
popularly called four-cycle and two-cycle motors, respectively.

A cycle, of course, can be any round of events, such as a cycle of
years--at the end of which time the previous happenings are scheduled
to repeat themselves. But in gas engine parlance a cycle is taken to
mean the round of events from, say, the explosion of one charge to the
ignition of the next. Thus, it will be seen that the four-cycle motor
requires four strokes of the piston to accomplish its round of events,
and is, properly, a four-_stroke_ cycle motor. Likewise, the so-called
two-cycle motor requires two strokes to complete its cycle and should
therefore be termed a two-_stroke_ cycle motor.

If this longer terminology could be adhered to, there would be less
misunderstanding of the meanings of two- and four-cycle, for when taken
literally, these abbreviated forms signify absolutely nothing. Usage
seems to have made them acceptable, however, and if the reader will but
remember that four-cycle, for instance, means four _strokes per cycle_,
the term becomes almost as simple as does "four-cylinder."

It is evident that there are two strokes for each revolution of the
flywheel--one when the crank is forced down and the other when the
crank moves up. As the piston is attached to the crank through the
medium of the connecting rod, the strokes are measured by the motion
of the piston. Thus, since it requires four strokes of the piston to
complete the round of events in the four-cycle motor, the explosions
occur only at every second revolution of the flywheel. In this
connection it must be remembered that we are dealing with but one
cylinder at a time, for a four-cycle engine is practically a collection
of four single-cylinder units.

But even though the explosion in a four-cycle motor occurs only every
other revolution, the engine is by no means idle during the interval
between these power impulses, for each stroke has its own work to do.
The explosion exerts a force similar to a "hammer blow" of several tons
on the piston, and the latter is pushed down, thus forming the first
stroke of the cycle. The momentum of the flywheel carries the piston
back again to the top of its travel, and during this second stroke all
of the burned, or exhaust, gases are forced out and the cylinder is
cleaned, or "scavenged." The piston is then carried down on its third
stroke, which tends to create a partial vacuum and sucks in the charge
for the next explosion.

On the fourth, and final, stroke of the cycle the piston, still
actuated by the momentum of the flywheel, is pushed up against the
recently-admitted charge and compresses this to a point five or six
times greater than that of the atmosphere. At the extreme top of this
last stroke, the spark is formed, causing the next explosion, and the
events of this cycle are repeated.

Now, inasmuch as on one up-stroke of the piston the charge must be held
tightly in place in order that it may be compressed, and on the next
up-stroke a free passage must be offered so that the exhaust gases may
be forced out, it is evident that a valve must be used as a sentry
placed at the openings to restrain the desirable gas from escaping
and also to facilitate the retreat of the objectionable exhaust.
Likewise, the force of the explosion must be confined to the piston on
one down-stroke in order that all of the energy may be concentrated
at the crank, while on the succeeding down-stroke a free passage must
be afforded to the charge so that it may be sucked in through the
carburetor. Consequently a second valve must be used to control the
inlet passage on the down-strokes and prevent the escape of the force
of the explosion through an opening that was intended as an entrance
for the fresh charge. Thus valves are a necessity on all motors in
which successive similar strokes of the piston do not perform the same
operations.

As quadrupeds and bipeds form the two great divisions of the
animal kingdom, so is the motor separated into the two main
classes of four-cycle and two-cycle engines. Even though to all
exterior appearances, the two types of motors may be identical,
the distinction, to the engineer, at least, is as marked as is the
difference between a stork and an elephant. The difference is somewhat
reversed, however, in that, while the elephant has double the number of
legs of the stork, the four-cycle motor has but one-half the number of
power impulses of its two-cycle cousin at the same speed.

In other words, there is an explosion in each cylinder of the two-cycle
motor with every revolution of the flywheel,--instead of with alternate
revolutions, as is the case with the four-cycle type. But the number
of events necessary to produce each explosion must be the same in both
types of motors, and consequently it is only by "doubling up" and
performing several operations with each stroke that the two-cycle motor
can obtain a power impulse with each revolution of the flywheel.

Starting with the ignition of the charge, as in the four-cycle motor,
let us see how the events are combined in the two-cycle type so that
all will occur within the allotted two strokes. Directly after the
explosion there is but one event that can happen if this force has been
properly harnessed, and that is the violent downward travel of the
piston. Just before the bottom of this downward stroke is reached,
however, an opening is uncovered through which the exhaust gases can
expend the remainder of their energy--which by this time has become
greatly reduced. Immediately after this another passage is uncovered
and the charge is forced into the cylinder under pressure, thus helping
to clear the cylinder of the remainder of the exhaust gases.

All of this takes place near the end of the down-stroke; and at the
beginning of its return, the piston closes the openings previously
uncovered for the passage of the exhaust gases and incoming charge, and
then compresses the mixture during the remainder of its up-stroke. Thus
the suction stroke and the "scavenging" stroke of the four-cycle motor
are dispensed with in the two-cycle type and every downward thrust of
the piston is a power stroke.

The two-cycle motor has been used in several notable instances with
great success on motor cars, but by far the larger majority of
automobile power plants are of the four-cycle type. In view of the
wonderful simplicity of the two-cycle motor, its small number of moving
parts, and its more frequent power impulses, it may well be asked:
"Why is this not in more popular use on the motor car?" The four-cycle
motor has but one power stroke out of every four, while only alternate
strokes of the two-cycle motor consume power without producing any.

This would seem to indicate that, for equal sizes and weights, the
two-cycle motor would produce twice as much power as the four-cycle
type--and this is true theoretically. But the four-cycle motor devotes
an entire stroke to forcing out the exhaust gases, or scavenging, and
another entire stroke to drawing in a fresh charge, and it is evident
that these operations can be done much more effectively in this manner
than when combined with several other events following each other in
such rapid succession as is the case with the two-cycle motor. In
the two-cycle motor the incoming charge must be diluted to a certain
extent with the exhaust gases which have not been entirely expelled,
and the intake valve port is uncovered for so short a time that unless
there has been very high compression in the base, the cylinder cannot
be entirely filled with the explosive mixture at high speeds. This
is described in greater detail in the last chapter of this volume.
Thus, while admittedly simpler in construction and operation than the
four-cycle, the two-cycle motor in its ordinary forms does not obtain
quite as high an efficiency from the fuel as does its more complicated
cousin. Each type has its distinct use, however, and in many instances
in which low initial cost and simplicity of design are more desirable
than are economy of fuel and high efficiency of operation, the
two-cycle motor stands supreme.

The sentries that stand guard over the passages through which the
gases make their entrance and exit may appear in a variety of guises,
but they determine the shape of the cylinders of a motor and divide
the four-cycle engine into a number of classes. For instance, if the
valves controlling the admission of the explosive mixture are placed on
one side of the cylinders and those officiating over the exit of the
exhaust gases are located on the opposite side, the motor is known as
the "T-head" type because of the shape of its cylinders.

All valves that are placed at the side of the cylinder must operate
in pockets so as not to interfere with the movement of the piston.
These pockets are cast with the cylinder and form a projection at its
side near the top. When these projections are cast on opposite sides,
a cylinder having the shape of the letter "T" is formed, while if the
valves operate on the same side, the single projection forms a cylinder
having the shape of the inverted letter "L." Hence cylinders having
valves on opposite sides are called "T"-head motors, while "L"-head
motor is synonymous for an engine having "valves on the same side."

When the valves are placed in the head, there is no need of separate
pockets, for these valves operate from above and do not interfere
with the movement of the piston. There may be a combination of these
positions, one set of valves being placed in the head and the others
at the side. This is known as the "inlet in head, exhaust at side"
type--or vice versa, as the case may be.

The valve that has been in almost universal use in motor cars is known
as the "poppet" type, as distinguished from the sliding and rotary
styles. As evidenced by its name, the poppet valve is pushed or lifted
from its seat, and thus the full area of the opening to the passage is
made available almost immediately. The poppet valve is lifted by a cam,
the shape of which determines the relative speed of operation of the
valve, and is returned to its seat by a stiff spring. The nature of the
contact that the valve makes with its seat depends upon the condition
of the surfaces and is the deciding factor as to whether the joint is
completely air-tight or not.

When the exhaust valve is opened, its head is thrust directly in the
path of the hot, out-rushing gases; these same gases also swirl around
the edge of the seat. The excessive heat and the particles of carbon
that are often found in the exhaust gases tend to corrode and build
a deposit on the edges of the valve and its seat, thus eventually
preventing perfect contact from taking place. This makes necessary the
grinding of the valves--an operation that is familiar to the majority
of motor car owners and drivers.

While the poppet valve motor is still used on the majority of
automobiles, a new and radical type of valve mechanism has been giving
successful results. This is known as the sliding sleeve type of motor,
and while it has been used for several seasons in Europe, 1912 saw
its adoption for the first time in America. The sleeve motor, it must
be understood, is of the four-cycle type, the events occurring in the
same order as on any ordinary automobile motor, and the only difference
lies in the nature of the valves that control the openings of the
exhaust and inlet passages. That this difference is great, however,
will be realized when it is understood that the valves consist of two
concentric shells, in the inner one of which the piston reciprocates.
In other words, two hollow cylinders line the interior of the cylinder
casting and replace the poppet valves and pockets of the more familiar
type of motor.

These sleeves, or shells, or hollow cylinders--or whatever name it is
chosen to give them--slide up and down in the same line of action as
that of the piston. A port, or slot, is cut near the top on opposite
sides of each of the shells. These four ports are so arranged that one
set opens directly opposite the intake passage, while the other opens
by the exhaust manifold entrance. When it is said that these ports
open, it is meant that similar slots in the two sleeves come opposite
each other, or "register," so that an unobstructed passage for the gas
is offered. The port in one sleeve may be opposite the intake pipe
entrance, but if the slot in the other sleeve does not correspond with
this, the passage is effectively closed.

Thus it will be seen that the ports are opened and closed by the
movement of the sleeves in opposite directions. For example, just
before the opening of the intake port, the inner sleeves will be
traveling upward while the outer shell moves downward, and the slots
in the two shells will be opposite each other at the instant that they
pass the inlet pipe. This gives a much quicker opening than would be
the case if one shell stood still while the other moved downward, and
it is because the slots approach each other from opposite directions
that this motor can be run efficiently at high speeds.

Inasmuch as this is a four-cycle motor and the explosions occur in each
cylinder but once during every two revolutions of the flywheel, each
sleeve makes but one stroke for every two of the piston. The sleeves
are operated by eccentrics attached to a shaft driven at a two-to-one
speed by the crank shaft of the motor, and as they are well lubricated
there is but very little friction generated between them and the
piston. In fact, it has been shown that the power required to operate
the sleeves, when well lubricated, is considerably less than that
consumed by the springs and valve mechanism of the poppet valve motor,
for the reason that the former type of valve does not open against the
pressure of the exhaust, as is the case with the ordinary gas engine
valve.

Besides the two- and four-cycle divisions, a motor is known by the
arrangement of its cylinders and is classified as "cylinders cast
separately," "cast in pairs," or "triple cast," according to whether
there are one, two or three cylinders to a unit. The last-named type
is not as common as are the "pair-cast" cylinders and of course can
only be used on six-cylinder motors.

When all of the cylinders of a motor are cast in one piece, the engine
is known as a "bloc" motor. This is a type that has come into popular
use for small and medium-sized power plants during the past few years
on account of the simplicity of its construction and the smooth and
compact design that is rendered possible. Of course it may be argued
that, with such a design, the entire set must be replaced if a single
cylinder is damaged, but castings have been so improved that an
accident or imperfection requiring the renewal of a cylinder is very
rare.

It is evident that, beyond a certain size of cylinder, a bloc casting
becomes too bulky to be handled conveniently, and as the entire casting
must be removed when it is desired to reach the connecting rods, crank
shaft, or piston rings, a motor so designed will seldom be found that
develops more than forty or fifty horsepower. This type of casting is
found on some six-cylinder cars, however, but it is naturally only the
"light sixes" that will use such a motor.

Above six-cylinders, a motor is usually arranged with its power units
set at an angle on either side of the vertical, thus forming the
V-shaped motor. Several eight-cylinder motors are so constructed, the
units being arranged four on a side and each set placed at an angle
of about thirty degrees from the vertical. This gives the effect of
two four-cylinder motors placed side by side and operating on the same
crank shaft.

In order to make the motor as compact as possible, the cylinders are
"staggered;" or, in other words, the cylinders of one set are placed
opposite the spaces between the units of the other. It will be seen
that the V-shaped design of motor shortens the power plant and enables
it to be set in a much smaller space under the bonnet than would be the
case were the cylinders placed one in front of the other, as in the
four- and six-cylinder types.

As a rule, the two-cylinder, four-cycle motor is of a different type
from its four- and six-cylinder cousins, and is known as a "horizontal
opposed" engine. In such a motor, the cylinders are set lengthwise
and the pistons operate opposite each other in such a manner that a
"long, narrow, and thin" power plant is obtained that is especially
well-suited for a location under the body of the car. In fact, this
horizontal motor, which may, of course, be of the four-cylinder type,
is the only shape that can well be used under the body or seat of a
touring car. In some small runabouts, however, the "double-opposed"
motor is used to good advantage under the forward bonnet, as in the
"big fellows."

There are, of course, many other features of design that serve to
differentiate one automobile power plant from another, but these are
details that do not serve to classify the motor, and the man who knows
whether his machine is two- or four-cycle; poppet or sleeve valve;
separate, pair, or en bloc cylinder castings; and "T"- or "L"-head
shape will have at his fingers' ends distinctions that would have
"floored" the salesman of a few years ago.




CHAPTER II

VALVES


It has been stated in the preceding chapter that the valves of the
gasoline motor are the sentinels placed on guard at the entrance to and
exit from each cylinder to make certain that the mixture follows its
proper course at the proper time.

Therefore, if we accept the definition that a valve is a mechanical
appliance for controlling the flow of a liquid or a gas, strictly
speaking no such thing as a "valveless" motor exists. Two-cycle
motors are sometimes said to be valveless because of the fact that
the movement of the piston automatically regulates the flow of the
exhaust and intake gases, but in this case the piston is in reality
the valve. On the four-cycle motor, however, like events take place
only on alternate strokes in the same direction, and consequently some
controlling mechanism that operates but once for every four strokes of
the piston is needed to time the flow of the gases.

As has been stated in the previous chapter, the most common form of
valve is known as the poppet type from the fact that its action is
a lifting one. Such a valve may be located in a projection cast on
either side of the top of each cylinder, or it may be inverted from
this position and placed in the cylinder head. When in the former
location, the valve is opened by an upward push on the rod to which it
is attached at its center, while a valve placed in the cylinder head is
forced down to allow the escape or entrance of the exhaust or intake
gases. The ordinary type of poppet valve is somewhat similar in shape
to a mushroom, having a very thin and flat head and a slender stem. The
disc portion of the valve is known as its head, while the rod forged
with the valve and by which the head is raised and lowered is called
the stem.

The projections cast in the cylinders of a "T"-head or "L"-head motor,
and in which the valves are placed, are known as the valve pockets.
Valves so located are lifted by a direct upward push caused by the
rotation of a cam and are returned to their closed position by means of
the extension of a stiff spiral spring surrounding each valve stem. It
is only the outer edge of the lower side of the valve head that comes
in contact with the surrounding surfaces of the opening which is closed
when the valve is returned to its ordinary position by the spring.

This surface of contact surrounding the opening is known as the valve
seat, and it is this, together with the edge of the valve which rests
against it, that must be ground smooth in order to insure a tight joint
when the valve is closed. On the majority of poppet valves the edge of
the head and the seat against which it rests are beveled to an angle
of approximately forty degrees in order to conform to the natural
direction taken by the gases when they are admitted or expelled. In a
few cases, however, the seat angle is ninety degrees, which means that
the edge of the head is ground flat, or straight, at right angles to
the stem.

One of the chief advantages found in the use of a poppet valve is the
fact that a large opening can be obtained after the valve head has
been raised but a comparatively short distance. This means that the
valve stem need travel only a fraction of an inch between the full
open and the full closed position of the valve and that the operating
mechanism for obtaining this lift is simple. Practically every poppet
valve, therefore, is lifted by means of a cam, which is a thick,
irregularly-shaped piece of steel mounted on a shaft known as the cam
shaft. If the end of the valve stem, or a rod connected to it, is
held against the periphery of the cam while the latter is revolved by
its shaft, the valve will be forced up, or away, rather, an amount
corresponding to the increase in distance between the periphery of the
cam at this point of contact and its axis.

In other words, if the cam were a true circle with its axis passing
through its center, there would be no motion of the valve, for all
points of the periphery of a circle are at the same distance from the
center. Consequently a portion of the periphery of the cam is extended
in the shape of a "nose," the projection of this beyond the smallest
diameter of the cam being the distance that the valve will be lifted
when this point of the cam surface comes in contact with the stem or
push rod. The broader, or more blunt, the nose of the cam, the longer
will the valve remain open as the cam shaft is revolved, while the
"slope" of the sides of the nose determines the rapidity with which the
valve will be pushed out and back. Inasmuch as the valve should remain
closed throughout two-thirds or three-quarters of every two revolutions
of the flywheel, the greater part of the periphery of the cam is
circular, or at the same distance from the axis at all points.

As has been mentioned before, the cam serves only to lift the valve,
the return of the latter to its seat being obtained by the force from a
spring that is coiled around the stem. Thus the spring holds the end of
the push rod at all times against the periphery of the cam. This push
rod, in some instances, is a small bar of special steel that slides in
guides of long-wearing bearing alloy. The upper end of the push rod
is in contact with the lower end of the valve stem, while its other
extremity is oftentimes designed in the form of a small steel roller
that thus serves to create a rolling contact with the periphery of the
cam.

In other designs, the lower extremity of the push rod may be in the
form of a specially-hardened steel pin with a rounded end, while still
a third type consists of a flat disc slightly "offset" on the end of
the push rod so that various points of its surface will come in contact
with the periphery of the cam and the wear will be evenly distributed.
Whatever the particular design, however, the cam is well lubricated
and both it and the push rod are intended to last as long as any part
of the motor.

Many motors are designed with one valve at the side and the other,
usually the intake, in the head. There are also many motors
manufactured that have both the intake and the exhaust valves located
in the head, in which case the valve pockets, or projections, are
eliminated. Such valves may be operated by the same type of cams and
cam shaft as those used to open the valves at the side. As the opening
of a valve located in the head is downward, however, the motion
produced by the cam on the push rod must be reversed in direction.
This reversal of motion is obtained by means of a lever mounted at
its center and placed in contact with the upper extremity of the push
rod at its outer end. The other end of this lever operates in contact
with the end of the valve stem, and thus an upward push on the rod is
converted into a downward thrust on the stem. This lever that reverses
the direction of the push rod motion is known as a rocker arm and is
mounted in a yoke cast with the cylinder head.

Inasmuch as a spring is used to keep the valve tightly closed when
the cam is not lifting the latter, it is the contact of the valve head
with its seat that must form the stop to the motion of the spring. It
will be seen that the force of the spring is communicated through the
valve stem to the push rod, and thence to the periphery of the cam when
the latter is in a position to lift the valve. The push rod should not
be forced tightly against the periphery of the cam when the valve is
closed, however, for this would prevent perfect contact between the
valve and its seat. Consequently there should be a certain amount of
"play" between the end of the push rod and valve stem so that it will
be certain that the head is forced against the seat with the full power
of the spring and without the cam serving as a stop.

On the other hand, this play should not be too great, for the cam and
push rod will then move an appreciable distance before the valve is
raised. This will cause the opening of the valve to occur late and
will reduce the distance that the stem is raised, thus restricting the
size of the opening. Furthermore, an undue amount of play between the
ends of the push rod and stem will result in a pound or "hammer blow"
between the two that is liable to wear the surfaces rapidly.

The "happy medium" that will give the best results may be obtained by
properly setting the small valve "tappets" that are secured to the
end of the stems or push rods. By turning the nut of the tappet in
one direction, the length of the push rod will be reduced, while the
reverse operation will increase the length of the rod or stem. This is
primarily intended for taking up any wear that may occur at the ends of
the push rod or valve stem. In the case of engines having the valves in
the head, the long push rod of each valve should be so loose as to move
perceptibly when shoved up and down by the thumb and finger.

When the rocker arm is pressed down against the valve stem, the space
between the other end of the rocker arm and the push rod should be
sufficiently wide to admit a piece of tissue paper. The same test may
be made in connection with valves located at the side, after first
ascertaining that the end of the short push rod is resting firmly
against the periphery of the cam. The play will be apparent, of course,
only when the valve is tightly closed, and in order to make certain
that their cams are in the "inactive" position, the piston should be
set at the beginning of the explosion stroke when testing the intake
or exhaust valve. This is at the point of ignition and is the time at
which both valves should be tightly closed.

The cam shaft to which the cams that operate the valves are attached
is generally placed inside the crank case. If the motor is of the
"T"-head type, having valves on opposite sides of the cylinders, the
cam shaft operating the exhaust valves will be found on one side of the
crank case, while that for opening the inlet valves will be located on
the other. If the motor is of the "L"-head type, all the cams will be
placed on the one shaft. The cams are sometimes forged with their shaft
in a solid piece, while in other designs they are keyed in place, but
whatever type is used, the cams and their shaft may be considered as
integral with each other.

The cam shafts are generally driven by a gear meshing with a smaller
one attached to the front end of the crank shaft of the motor, which
forms one of the forward train of gears that are enclosed in an
aluminum case. If the cam shaft is driven at the same speed as is
the crank shaft of the motor, it will be seen that the valves will
open once at every revolution of the flywheel. In a four-cycle motor,
however, the explosion and other events occur but once in each cylinder
for every two revolutions of the flywheel, and consequently the cam
shaft must be driven at one-half the speed of the crank shaft.

To obtain the proper speed ratio, each cam shaft is driven by a
"two-to-one" gear, which means that the gear on the end of the crank
shaft has but one-half as many teeth as have those attached to the cam
shafts. There is thus one revolution of each cam shaft gear for every
two of the crank shaft gear, and consequently each cam shaft is driven
at the required half speed.

The cam shafts may be driven by a chain, the links of which fit over
teeth cut on sprocket wheels, but there must always be a constant
relation between the position of the cam shaft and that of the crank
shaft. This constant relation is necessary in order that the valves
will open and close at the proper points during the travel of the
piston. For example, the exhaust valve should open toward the end of
the explosion stroke in order to allow the burned gases to be forced
out, and the cam for operating this valve should always be in the
lifting position at exactly the proper moment.

If the cam shaft is not positively driven, this position may change and
the exhaust valve might be opened at the beginning of the ignition
of the charge, in which case the force of the explosion would be
wasted almost entirely. On the other hand, the inlet valve should
open at about the beginning of the suction stroke in order that the
fresh charge may be drawn in by the downward travel of the piston;
it is evident that this cannot be opened at any other time without a
resulting loss in the power developed by the motor.

The proper timing of the action of the valves is consequently one of
the most important adjustments of a motor. When the motor is assembled
and tested at the factory, the valves are properly timed and there
is no possibility that they will require further adjustment in this
respect until after the engine is "taken down" for the purpose of
cleaning or the renewal of a broken part. If it should ever become
necessary to remove one of the cam shafts or any of the gears
constituting the forward train, the greatest care should be taken
to make certain that all are returned to _exactly_ their original
position. A difference of one tooth in the relative meshing of the
gears may result in a loss of fifty per cent. of the power developed by
the motor.

Absolute rules for the proper timing of the valves cannot be given
here, for various motors are designed with slightly different
positions at which the exhaust and inlet valves should be opened and
closed. A cam shaft should never be removed, however, without first
marking the intermeshing teeth of its driving gear and those of its
companions. This may best be done by means of a small prick punch
which, when tapped lightly with a hammer, will make a permanent mark
at the desired point on the surface of the gear. If the motor is of
the "T"-head type, having its valves operated by two cam shafts, care
should be taken to designate the right and left-hand gears so that
their positions will not be reversed if both have been removed at the
same time.

A safe method to pursue is to indicate the right-hand gear with one
punch mark, while two should be used for the gear at the left. Three
teeth should be marked on each pair of intermeshing gears. That is, a
tooth on one gear should be marked, and then each of the teeth between
which it meshes on the other gear. The second cam shaft gear should be
marked before the motor is turned.

As has been stated, the cams on many motors are forged integral with
their shafts, and there is consequently no possibility of the removal
of one from the other. Those cams which are keyed to their shafts are
accurately and rigidly set and the keyways so cut that there is slight
chance of a mistake in returning a cam that has been removed. It should
seldom be necessary to remove a cam from its shaft, however.

Many motors are provided with timing marks on the flywheel to indicate
the positions of the latter at which the valves of the various
cylinders should open and close. In connection with these marks a
pointer attached to the crank case and indicating the top of the
flywheel is used. When the  marked, for example, 4
Ex 0, is under the pointer, it indicates that the exhaust valve on the
fourth cylinder should be about to open. If the motor is turned but
very little beyond this point, a lifting should be felt at the proper
push rod or valve stem.

It is well to test the setting of the valves occasionally by means of
these marks, for wear at the rocker arms, the push rods, the valve
stem, or the cam travelers will result in unevenly-timed valves. It
should be remembered that it is the valve itself that should open
after the proper mark on the flywheel has been passed, and that the
movement of a long push rod is not sufficient evidence that the valve
is beginning to leave its seat. There may be so great an amount of lost
motion between the push rod, cam, rocker arm, and valve stem that the
flywheel may be turned several degrees beyond the proper point before
this "play" will be taken up and the valve itself will begin to move.

Although the timing of a motor may be given in inches of piston travel
beyond a certain dead center, at which point an exhaust or inlet valve
should open or close, it is generally expressed in degrees of flywheel
revolution. Suppose, for example, it is said that the inlet valve
should open ten degrees after the beginning of the suction stroke. This
would indicate that the flywheel should be turned through an arc of ten
degrees from the point at which the piston is at its upper dead center
before the inlet valve for that particular cylinder should begin to
open. Expressed in terms of flywheel revolution, the total travel of
the piston during each stroke is 180 degrees, and as in the proximity
of its dead centers the piston moves but a short distance in comparison
with the size of the arc through which the flywheel swings, valves may
be set very accurately by this method.

Not all cam shafts for operating the valves are located in the crank
case. On several designs of motors the cam shaft extends along the top
of the cylinders and is driven by a vertical shaft and two sets of
bevel gears. On such motors both inlet and exhaust valves are located
in the cylinder heads, and owing to the proximity of the cam shaft, but
short push rods and valve stems are needed. The valves are sometimes
operated by means of a bell crank or rocker arm that acts directly
against the cam surface and end of the valve stem.

On some designs a double cam is used which serves to operate both the
inlet and exhaust valves of the cylinder. The bearings and cams of such
a shaft are generally enclosed in oil and dustproof casing screwed to
the top of the cylinders. Such a cam shaft should never be dismounted
without first marking intermeshing teeth of all spur and bevel gears
that are concerned in its operation.

All poppet valves must be accessible and readily removable for the
purpose of cleaning and grinding the contact surfaces of the head and
seat. The pockets in which the valves placed at the side of a cylinder
are located are generally provided with large screw plugs at the top.
Such a plug may be removed with a heavy wrench, and as the opening
which it fills is larger than the head of the valve, the latter may be
removed after first loosening the spiral spring surrounding its stem.
It is not necessary to remove the valve entirely from its pocket in
order to grind its surfaces, but the pin holding the spring stop in
place must be withdrawn so that the tension of the spring on the valve
will not be so great as to prevent the latter from being lifted to
permit the introduction of the abrasive and turning the head with the
grinding tool.

Valves located in the head of the cylinder must be removed entirely
before their surfaces can be ground. This, however, is not a difficult
operation, as the valve and its seat are generally placed in a
removable "cage" that either screws in place or is held firmly in
position by means of a clamp or like device. Inasmuch as the seat is
contained in this removable cage in which the valve operates, the
grinding may be done at a work bench or on the bed of any convenient
tool, independently of the location of the motor.

If a valve seems sluggish in its action at high speeds of the motor, it
is possible that its spring has become somewhat weakened. These springs
are designed to be exceedingly stiff and heavy, some of them requiring
a pressure of two hundred and fifty pounds to compress the coils one
inch. With such a spring, a special tool is required to compress it
sufficiently to enable the valve to be removed. A spiral spring that
has become weakened may sometimes be strengthened by "stretching," but
it is not to be supposed that this would be of great avail in the case
of a spring as heavy as those used on some valves. If, however, a flat
tool is introduced between the various coils and each is separated
slightly so that the ultimate length of the entire spring is greater
than it was formerly, it will exert a more powerful force on the valve
when it is returned to its place surrounding the stem.

Stiffening the spring, however, will be of but little help if the stem
or push rod is tight in the guides through which it slides. These
guides are often made of a special bearing bronze and are designed to
withstand a large amount of wear, but the friction surfaces must be
lubricated if satisfactory service is to be obtained. The lower guide
is generally lubricated by the oil from the cams, while the guide
near the valve may receive its oil from the engine cylinder. It is
not necessary that these guides shall be packed or that they shall be
particularly tight, as they are not called upon to retain any gas or
air pressure, but they must hold the stem and rod sufficiently rigid to
prevent any perceptible side motion and thus cause imperfect seating
of the valve. In replacing valve stems and push rods, it should be
made certain that each works freely in its guide before the spring is
installed. If there is a slight tendency for the guide to grip the rod
or stem, the latter should be smoothed with emery paper at the point
at which it comes in contact with the guide and plenty of oil applied
until the surfaces are well "worked down." As the distance that the
rods and stems travel through the guides is comparatively short, the
wear is slight and only a small amount of lubricant is needed, provided
the rubbing surfaces are smooth and well-fitted to each other.

The mechanism of a sleeve valve motor is slightly different from that
of the poppet valve type. Each sleeve is operated by a connecting
rod and eccentric mounted on a shaft driven by a chain or gears from
the crank shaft of the motor. The eccentric replaces the cams of the
poppet valve motor, and as it must maintain a certain relation with the
position of the piston in order that the operation of the valves shall
be timed correctly, the same care must be observed in replacing the
eccentric shaft with the proper teeth of the sprocket or gear in mesh
as has already been described in connection with the cam shaft of the
poppet valve motor.




CHAPTER III

BEARINGS


In the general meaning of the term, a bearing is any part that carries
weight or pressure and at the same time rubs over another surface.
According to this definition, the portion of the cylinder walls
traversed by the pistons are bearings, and that is in reality the case,
but the term has come to be applied more specifically to the part of
the machine in which another part _revolves_, either continuously or
intermittently. Thus the portions of the crank shaft on which it is
supported and the parts of metal in which they revolve combine to form
the crank shaft bearings. The shaft or stud on which a gear or wheel is
mounted and on which it revolves is the bearing of that gear or wheel.

Although they are concealed, as some six-cylinder motors may be
provided with as many as three dozen, or more, bearings--if we consider
those on which the cam, pump, and magneto shafts and the gears are
mounted--but what descriptions, rules, and precautions apply to all
hold true in the largest sense when the crank shaft, connecting rod,
and wrist pin bearings only are considered. It is on this latter class
that the greatest wear of the motor is concentrated, and the owner who
understands and inspects these need fear no trouble from the cam shaft
and gear bearings.

The expert will judge of the condition of a motor by the wear that has
occurred in the bearings rather than by any exhibition of temporary
power that it may develop in a short test, and it is for this reason
that the "general public" runs a risk whenever it buys a second-hand
car that has not been thoroughly overhauled by a reputable factory or
inspected by a competent engineer. The bearings are in reality the
vitals of the motor, and when these are worn beyond the point of easy
adjustment or renewal, the repairs necessary to place the machine in
good condition would oftentimes cost more than the entire engine is
worth. But even in a badly-worn motor, the bearings may be "taken up"
and "doctored" so that, for a while at least, the engine will seem to
run perfectly and develop its full power. This will not be for long,
however, and soon the motor will begin to pound, knock, and rattle
until an examination will bring to light the true condition of the
bearings.

In no machine are the bearings subjected to more severe usage than in
the automobile motor. In order that the motor car power plant shall
be light in weight and occupy but a small amount of space, the power
must be transmitted at high speeds. In many an automobile motor, the
pressure imparted to a single bearing during a certain portion of its
revolution may frequently be well over two tons, and in this same
bearing, the "speed of rubbing" may approach eight or nine hundred feet
per minute. In other words, at normal speeds of the motor, about a
sixth of a mile of steel surface will rub over a certain point in each
crank shaft bearing during every minute that the engine is running.

When properly lubricated, an iron or steel shaft will run in almost
any kind of a metal bearing that is sufficiently strong to carry the
weights and pressures imposed upon the shaft. The friction generated
between two different metals that rub against each other, however,
varies according to the composition of those metals, and consequently
it is advisable to employ some material for a bearing that will offer
a minimum resistance to the turning of the shaft. Friction must be
reduced between all moving surfaces in order that the mechanical
efficiency of the machine shall be high, and it is in the bearings that
a large amount of power may be absorbed.

But even between the best-lubricated surfaces, employing the most
efficient metal as a bearing, some wear is bound to occur. The crank
shaft of a four- or a six-cylinder motor is forged or sawed from
one piece of steel, and with the accurate machining, finishing, and
grinding to which it is subjected, it becomes an expensive part of
the engine. Consequently it is advisable that the wear of bearings
of such parts shall be restricted to the "boxes" or surrounding
stationary metal in which the shaft revolves at these points. In order
that all wear shall occur here, rather than in the shaft, the boxes
are made of or lined with a softer metal. If the crank shaft is of
hard steel, the bearing metal may be of brass or bronze, but it has
been found that babbitt metals give the most satisfactory service for
such conditions--particularly as a sufficiently hard crank shaft is
difficult to produce commercially.

Not only is a babbitt metal softer than the steel of the shaft and
consequently receives practically all the wear of the bearing, but it
has the added advantage of melting at comparatively low temperatures.
At first thought, this may seem like a doubtful advantage, but in case
of a failure of the oil supply to that bearing, this characteristic may
be the means of saving the crank shaft, and possibly the crank case,
cylinders, and connecting rods, from rack and ruin.

The purpose of lubrication is to reduce friction between the two
surfaces in contact. Friction generates heat, and consequently the
temperature of a bearing to which a sufficient supply of oil is not
delivered will be raised to a very high point. This high temperature
will cause both parts of the bearing to expand, with the result that
the fit becomes very tight and the shaft binds or "seizes" in its box.
This is the familiar "hot box," so often the bane of railroad men, and
if the shaft is still run under these conditions, the bearing material
will be torn out and the surface of the shaft, axle, or whatever the
revolving portion happens to be, will be cut and abraded, oftentimes
beyond the possibility of repair. It is such accidents as these that
are prevented by the use of an easily-melted babbitt metal.

If the oil supply becomes insufficient so that the temperature of the
bearing is raised above a certain point, the babbitt metal will be
melted and will run out of its container before any damage can be done
to the shaft. Efficient running cannot, of course, be obtained with the
bearing "burned out" in this manner, but the babbitt is quickly and
easily renewed and serves as a sort of fusible safety valve that saves
many an expensive crank shaft replacement.

Babbitt metals may be of various compositions and proportions and many
contain lead, but those which have been found to give the best results
for use on the crank shafts of automobile motors are composed only of
tin, antimony, and copper. If lead is used at all for this purpose,
it should not appear in proportions above one per cent of the total
composition. Inasmuch as a babbitt metal will fuse at a comparatively
low temperature and is much softer than steel, it is obvious that such
a material will not withstand heavy pressures unless reinforced and is
unsuited for structural purposes. Consequently the babbitt is placed
in the bearing box in the form of a thin lining within which the shaft
revolves.

When the shaft is "lined up" in the box, the hot babbitt metal may be
poured in until the space is entirely filled. When the babbitt cools,
the shaft may be turned, and when lubricant has been introduced in
the oil grooves which should have been provided for the purpose, the
new bearing will be ready for use. It is not to be expected that the
majority of motor car owners will rebabbitt the crank shaft bearings
themselves, but it is necessary to understand the general principles of
such bearing design in order to inspect the motor intelligently and to
determine upon the repairs needed.

The above method of renewing "burned out" bearings applies to babbitts
in general, but the severe usage that automobile engine crank shaft and
connecting rod bearings are called upon to withstand necessitates the
exercise of a certain amount of additional care. It is necessary that
the box shall fit the shaft perfectly, so that there can be no "play,"
and yet the shaft must be allowed to turn easily within its surrounding
babbitt metal.

As was stated above, the shaft may be easily loosened from the babbitt
metal after the latter has cooled, and this would form a satisfactory
type of bearing were it not advisable that some means be supplied by
which the wear could be taken up without renewing the entire babbitt
lining. The bearing boxes of the crank shaft are each made in two
halves, the lower portion being cast integral with the crank case,
while the upper half is in the form of a separate cap that may be held
in place by two or four bolts. In this case, it is necessary that
the boxes shall be in two sections, for the shape of the crank shaft
prevents it from being slid into place lengthwise, and consequently it
must be placed on its bearing from the top. In some designs of motors
the bearing caps form the lower half of the box, but as in this case
the base of the motor must be inverted in order to remove the crank
shaft, the caps will still be considered as the "top" halves of the
boxes.

There may be dove-tail grooves cut in the inside of the halves of the
boxes to retain the babbitt metal after it has been poured in place.
Consequently, in order to remove the cap after renewing the babbitt
lining, the babbitt metal must be cut in two at the joint between the
two halves of the box. The two halves of the box, instead of fitting
closely together, are separated by thin strips of copper or fiber known
as "shims" that serve to relieve the shaft from the pressure of the
bolts when the bearing cap is screwed in place. In other words, the
two halves of the box must be held tightly in place by means of the
bolts and nuts, but none of this pressure should rest on the revolving
shaft, as this would bind it and prevent it from turning easily.
Consequently by "building up" the space between the two halves with
these thin shims the proper adjustment may be obtained.

These shims provide the method of taking up the wear in the babbitt
that will eventually result. By loosening the box retaining bolts and
removing the required number of shims, the halves of the box will be
brought closer together. When the bearing cap is screwed securely in
place, the shaft should be able to revolve freely without binding, and
yet the fit should be sufficiently tight to prevent any "play" at right
angles to the length of the shaft.

The pressure of a shaft should not be concentrated in one place, but
should be distributed over as large a surface of the babbitt metal as
is possible. A few years ago, when renewing or repairing a bearing, it
was considered sufficient to pour in the molten metal or to remove the
proper number of shims--and the bearing was then said to be ready for
its work. But even though no play was apparent, it was possible that
the shaft rested on only a few portions of the bearing surface; and
the increased attention that is now paid to the details of automobile
construction is no better exemplified than in the fact that nearly
all bearings are "scraped" in. This operation is simple and consists
merely in removing any slight excess babbitt metal so that the lining
fits the shaft throughout its entire length and circumference. The
babbitt is sufficiently soft to enable it to be peeled or scraped with
a sharp tool provided for the purpose, and no great degree of skill is
necessary in obtaining the required fit.

In order to determine at exactly what portions of the babbitt lining
the pressure is too great, a dye or paint known as "blueing" is used.
The bearing portion of the crank shaft is painted with this, and the
cap is then screwed in place. If the crank shaft is then turned and the
cap removed, it will be found that the blueing has been transferred
from the bearing to the portions of the babbitt metal on which the
pressure is the greatest. These portions should then be shaved with the
tool mentioned above, and the same test repeated. As the excess metal
is removed, it will be found that the blueing gradually is deposited
over a larger area of the babbitt, but it is not to be supposed that
the fit can be made so perfect that the color will be distributed
evenly over the entire surface. Care should be taken to screw the
bearing cap onto the shims as tightly as possible each time the blueing
test is to be made.

There is nothing that will heat a bearing so quickly as a poor
alignment of the shaft supported by it. For this reason gasoline engine
crank shafts are made exceptionally strong and heavy, especially those
that are supported only at their extremities, or at these points and in
the center of their length. A shaft that is bent or twisted to even the
slightest degree will soon "burn out" all of its bearings, regardless
of the amount of oil that may be fed to them. This is because of the
unequal pressures on the different sides of the bearing that allow no
room for the admission of the film of oil or other lubricant that is
necessary in all cases to prevent a "hot box."

On the other hand, the bearings must all be in perfect alignment, for
to set one slightly "off" would produce the same result as though the
shaft were bent. It will be seen that the use of babbitt produces a
"self-aligning" bearing, for the straight shaft may be set in its
proper position and the molten metal poured around the interior of the
boxes.

As it is highly important that the cap screws or nuts holding the
bearing cap in place should remain set as tightly as possible,
precautions must be taken to prevent any of these from working loose.
This may be done by means of a cotter pin that passes through a hole in
each bolt and through a pair of corresponding notches cut in the top of
opposite faces of the nut. A notch is generally cut in the top of each
face of the nut in order that the latter may be held securely in place
in any position. A continuous wire passing through all of the bolts and
nuts is sometimes used instead of the individual cotter pins.

Many modern automobile motors are designed with the crank shaft running
in ball bearings. The type generally used consists of a row of balls
set between the inner and outer edges of two concentric rings. The
inside of the outer and the outside of the inner ring are grooved,
constituting the ball "race" which forms the surface upon which the
balls roll and which, at the same time, serves to hold them in place.
Each ball of the same bearing must be made of exactly the same size as
its companions--or at least within one or two ten-thousandths of an
inch--and each one must be large enough and of sufficient strength to
withstand, by itself, the entire pressure in that bearing. The inner
ring slips over the bearing portion of the shaft with a comparatively
tight fit, while the outer ring remains stationary in its bed in the
crank case.

The inner ring turns with the shaft, thus causing the balls to roll in
their race. Each ball rolls about its own axis, and the entire series
describes a circular motion in the same direction as that taken by
the shaft, but considerably slower. Consequently there is no rubbing
in such a bearing, all the motion being of the rolling type, and as
this reduces friction to a minimum, the balls may be run without oil,
although lubrication of the proper kind would certainly not harm the
bearing. Ball bearings are adapted only for a two-bearing crank shaft,
for inasmuch as the rings must be slipped over the shaft, it would be
manifestly impossible to provide a ball bearing in the center, or in
any other portion beyond a crank.

Next in importance to the main bearings of a crank shaft are those by
which the connecting rods communicate their motion to the cranks. These
are known as the crank pin bearings or the "big end" of the connecting
rod bearings. But inasmuch as the upper, or smaller, end of the
connecting rods are termed the wrist-pin bearings, the other end may be
called simply the connecting rod bearing.

The connecting rod bearings are similar to the main bearings described
in the foregoing pages and are renewed and adjusted in the same manner.
It is probable, however, that these receive a greater amount of wear
than do the main bearings, inasmuch as the former obtain the direct
impact of the force of each explosion. Furthermore, the box of the
connecting rod bearing describes a complete circle with each revolution
of the crank shaft, in addition to the "internal rotation" of the
crank, while an alternate push and pull is delivered to it by the
connecting rod on its various strokes.

Consequently it is the connecting rod bearings that will become loose
and require "taking up" before any attention need be bestowed on the
main bearings. The wear will increase in the connecting rod bearing as
the play becomes greater, and if matters are not remedied, the box may
eventually be broken, with the result that the end of the connecting
rod thus freed will start on the "rampage" and will punch several
pieces out of the bottom of the crank case.

Brass or bronze bearings may be used at the big end of the connecting
rods, but the large majority of motor car engines are provided with
babbitted bearings at these points. It is especially necessary that
these bearings should be scraped to a perfect fit and that the shims
should be adjusted properly so that no side play will be apparent
when the connecting rod is moved transversely to the length of the
crank shaft. When renewing the babbitts of connecting rod bearings
care should be taken to allow the connecting rod to swing free before
the molten metal is poured in. If this is not done, the connecting
rod may be forced slightly to one side or the other and will be held
permanently in this position when the babbitt cools. This will induce
a slight side thrust in the connecting rod, which will be communicated
to the piston, with the result that the side of the latter and of the
portion of the cylinder wall against which it moves will be scored and
worn unduly.

Inasmuch as the connecting rod bearings are subjected to such a variety
of strains, and as looseness at these points will result in serious
wear, it is doubly necessary that the nuts and bolts holding the
bearing caps in place should be securely wired or held tightly by means
of the previously-mentioned cotter pins. It is evident that the base of
the large end of the connecting rod forms the upper half of the bearing
box, while the cap constitutes the lower end and is attached from the
bottom.

The connecting rod bearings on some motors are hinged at one side so
that the cap may be turned away from the crank shaft when it is desired
to remove the connecting rod. In this case the hinge replaces the one
or two bolts or nuts on one side of the box and is held in the proper
position by those on the other side. While it may be easier to adjust
a bearing provided with such a cap, the results obtained can hardly
be expected to be as satisfactory for high-grade service, as is the
case when the shims may be used on both sides of the two halves of the
bearing.

The wrist-pin bearing is located at the upper, or small, end of each
connecting rod, and, although it also carries the full force of each
explosion, it is not subjected to as great wear as is the bearing at
the other end of the connecting rod. The reason for this is that this
bearing does not revolve and its friction surface is reduced to the
comparatively small arc through which the connecting rod swings. Wear
can occur here, however, and because this bearing is more inaccessible
than is the crank shaft or connecting rod bearing, trouble at the wrist
pin is often overlooked.

The wrist pin can only be reached by the removal of the piston and
connecting rod. In the majority of designs the wrist pin is placed
in the sides of the piston and is held stationary by small keys or
by set screws. In this case, the bearing surface is formed by the
wrist pin and the small end of the connecting rod, at which point the
greatest wear occurs. This bearing is never babbitted, but in order to
reduce the wear on the wrist pin--which is generally made of hardened
steel--the circular opening in the upper end of the connecting rod is
lined with a bronze or brass bushing that forms a bearing fit over
the wrist pin. It is this lining, or bushing, that will wear rather
than the hardened steel wrist pin, but as the former is easily removed
and is not expensive to replace, the renewal of this bearing is a
comparatively simple matter.

In other types of wrist pin bearings, the pin is held stationary in the
connecting rod opening and turns with it as the connecting rod swings
through its arc on each stroke of the piston. With such a design, the
bearing surface is formed by each end of the wrist pin and the openings
in the sides of the piston walls in which the wrist pin rests. In order
to form an easily-replaced bearing surface, these openings in the
piston walls are lined with brass or bronze bushings that receive the
major part of the wear, as has been described in connection with the
bushings fitted to the opening at the small end of the connecting rod.

There is nothing complicated or mysterious connected with the renewal
or repair of bearings, but the man who makes such replacements or
adjustments must be an accurate and careful worker, and while he
need not be a "born machinist," he must at least possess the "knack"
of handling tools properly. And he must, above all, realize that
the designers and manufacturers of his motor have been dealing in
measurements of the thousandth part of an inch and that too great care
cannot be taken in the repair of bearings to obtain a perfect fit.

If he is renewing a connecting rod or a wrist pin bearing, he must
also remember that the piston has formerly been traveling over a
certain area of cylinder surface that has not varied in length the
ten-thousandth part of an inch between one stroke and the next.
Consequently, the babbitts or bushings should be so replaced that the
piston shall occupy the same position relative to the cylinder walls at
the top and bottom of its stroke that it did formerly. In other words,
by varying the thickness of the top of the babbitt he is replacing, he
may change the "center" of the bearing so that the piston will start
on its upward stroke from a different point than was previously the
case. Thus, while the length of travel of the piston will be the same,
it will traverse a slightly different portion of the cylinder walls
under the new conditions, and this will have the effect of changing the
compression and, possibly, of wearing the piston and rings unduly.




CHAPTER IV

THE IGNITION SYSTEM


It was the application of the electric current to the ignition system
of the gasoline engine that first enabled these new forms of power
plants to be designed with sufficient compactness and to possess
enough flexibility to render their use practical on self-propelled
vehicles. Without the electric ignition system, the speed and power of
the vehicle could not well be controlled, and the explosions would be
uncertain and irregular, at best.

Those of us who are familiar with the electric gas lighters that
were in popular use a few years ago are furnished with a convincing
demonstration of the operation of the first electric ignition systems.
By pulling a chain, a wire, or arm was rubbed across a metal point
until the contact thus formed was suddenly broken. This arm and the
stationary point formed the two terminals of an electric circuit, which
caused a flash of blue flame when the contact was broken as the one
was "wiped" across the other. The flame thus formed at the instant the
contact was broken contained sufficient heat to ignite the gas escaping
from the burner to which the device was attached.

Sparks will be formed in the same manner if we hold two wires,
connected to the opposite poles of a set of batteries, in both hands
and wipe the bare ends across each other. If an arrangement producing
this effect is introduced into the gas engine cylinder at the portion
in which the charge is compressed, the flash resulting when the
terminals are separated will serve to ignite the explosive mixture.
The movable terminal is connected to a rod which passes through the
cylinder walls and is attached to a mechanism actuated by a cam
revolved by the engine. This mechanism is termed the "make-and-break"
ignition system for the reason that contact of these terminals is
alternately made and broken to produce the flash of electricity that
explodes the surrounding charge.

In order to produce a flash of sufficient size when the contact is
broken, the nature of the current, obtained from the dry cells or
storage battery is changed somewhat by conducting it through a coil of
wire surrounding a bundle of bare copper wires. This is known as a
spark coil, and while it is generally used with battery ignition of the
make-and-break type, magnetos may be designed which produce the proper
kind of current direct, without the aid of the coil.

An ordinary set of six dry cells, connected in series--or like with
unlike poles--will produce a current of between twenty and twenty-five
amperes at a pressure of about nine volts--assuming each battery, when
new, to deliver twenty-five amperes at a pressure of one and one-half
volts. The "series" wiring gives the entire set the combined voltage
of all with the average amperage of one. For the benefit of those who
have forgotten their elementary physics, let it be remembered that the
ampere is the measure of current _amount_, or flow, while the voltage
is concerned only with the _pressure_ of the current. By the use of
various arrangements of windings of wires, the voltage may be raised
with a corresponding decrease in the amperage--and vice versa. Thus, if
a coil is used that doubles the original number of amperes produced by
the battery, the voltage will be halved.

The make-and-break type of ignition has been used successfully for many
years, but with the perfection of the magneto, it has been largely
supplanted, in automobile practice, at least, by the "jump spark," or
"high-tension" system. Because of the fact that the latter system is
less expensive to construct and is highly efficient, it will be found
also on the majority of the older cars not equipped with a magneto.

It was found, after the general adoption of the make-and-break
ignition system, that a flame was not necessary for the combustion of
a properly-mixed charge in the engine cylinder. In fact, a tiny spark,
scarcely one-sixteenth of an inch long and no larger around than a
pin, was discovered to be sufficient to produce the ignition of the
charge. Although, of small volume, such a spark generates intense heat,
and it is upon this quality, rather than upon area, that the charge
depends for its ignition--although it is claimed that a large flame
will produce more complete, rapid, and consequently more efficient,
combustion. But the jump spark possesses the advantage of requiring no
moving parts projecting through the cylinder walls into the combustion
chamber, and its greater simplicity over that of the make-and-break
system has resulted in its almost universal adoption by automobile
manufacturers.

It has been stated in a preceding paragraph that the voltage produced
by the average battery set will not exceed nine or ten, and even the
pressure generated by the ordinary magneto is not greater than this.
But air is not a good conductor of electricity and forms a very high
resistance to the passage of a current. It is only when the high
resistance of an air gap is encountered in its circuit, however, that
a spark will be formed by the current, and consequently the form
of electricity used in this system must have resistance-overcoming
properties. But it is only by raising the voltage of the current that
even a short air gap can be bridged by the spark. In fact, a pressure
of somewhat over fifty thousand volts is required to produce a spark
less than an inch long in the air.

Although only called upon to jump a gap about a sixteenth of an inch
across, the ordinary high-tension current is capable of bridging a
space eight or ten times this width in order that ample pressure will
always be assured for the formation of the spark. Furthermore, the
warm gases in which the spark is formed in the cylinder increase the
resistance ordinarily encountered and it is consequently necessary to
raise the voltage above the amount that would be needed were the plug
exposed to the open air.

These conditions make advisable a pressure of from twelve thousand to
thirty thousand volts in the ordinary jump spark system, and it is
from this voltage that the term "high tension" is obtained. The nine
or ten volts delivered by the batteries are transformed to this larger
amount by means of an induction coil--or what is more generally termed
merely the "coil." This is in reality a "step-up" transformer, since
it transforms the current from one of low voltage to another of two or
three thousand times its original pressure.

This transformer consists of two coils of wire, one surrounding the
other. The inner coil is composed of a comparatively few number of
turns of rather coarse wire wound around a soft iron core, and is
termed the "primary" winding, since the current from the batteries is
led directly through it. The outer coil is composed of many turns of a
very fine wire, all of which are thoroughly insulated from each other
and from the inner winding. This outer coil is termed the "secondary"
winding and is the one from which the high-tension, or transformed,
current is taken.

This secondary current is "induced" from the primary winding through
which the battery current passes and possesses a voltage that has
increased over its original amount in the same proportion that the
number of turns in the secondary winding bears to those in the
primary. Therefore, if the original battery voltage is ten and there
are a thousand times as many turns in the secondary winding as in the
primary, the resulting high-tension current will have a pressure of ten
thousand volts.

The principle of the coil is dependent entirely upon that peculiar
electric property known as "induction." Around every wire through which
an electric current passes are invisible "lines of force" similar
to those that emanate from an electro-magnet. These lines of force
surround the wire throughout its length, and arrange themselves in a
spiral formation. Insulation has no effect on these lines of force,
and they may be collected from wires which are separated from each
other by several thicknesses of current-confining material. It is, of
course, necessary to use insulated wires in the construction of these
coils, for otherwise the current would merely pass to adjoining turns
and would not travel the entire length of the winding--and therefore as
great a number of lines could not be collected.

If an additional layer or layers of wire is wound around the first
series of turns, the lines of force will be collected, or "induced,"
by this second coil, and will constitute the secondary current. The
induction effect is greatly increased if the primary current is allowed
to accumulate, or "pile up," and discharge, alternately, for this
surging of the current creates a sort of "overflow" from the original
containing wires.

Ohm's Law, which states that the number of amperes in an electric
circuit is equal to the voltage divided by the number of ohms of
resistance encountered, shows that the current will be changed by its
passage through the primary winding. The induced current is further
changed, and when collected by the secondary winding and sent through
its long coils, we have the high-tension circuit mentioned in the
preceding paragraph.

If the reader remembers that it is but one hundred and ten volts that
is used to operate our electric lights and that five hundred will run a
trolley car, he may wonder why it is not dangerous to handle as great
a pressure as the thirty thousand volts that are used in connection
with the ignition system of a motor car. But it is the combination
of great voltage with high amperage that is dangerous, and if it is
remembered that, as the former is increased, the latter is reduced
correspondingly, it will be realized that the ordinary high-tension
ignition current possesses a _quantity_, or flow, of scarcely one
one-hundredth of an ampere.

If we liken the electric current to a flow of water in a pipe, we have
the amperes corresponding to the quantity of the flow, or the number
of gallons that will be delivered at the outlet in a given time.
Continuing this analogy, the voltage of the electric current will be
the pressure, or "head" in the water system, and the current from the
batteries before the coil is reached will correspond to a moderate
flow of water at a comparatively low pressure. After the coil has
transformed the current to the high voltage, we have the conditions
of a very small opening in the water pipe containing a tremendous
pressure. Such a stream will possess but small flow, but its high
pressure will enable it to be "squirted" to a far greater distance than
would be the case were its volume larger and its "head" less. Although
the pressure is high, its quantity is so low that the stream can do but
little damage and would scarcely more than tickle the flesh of a person
against whom it is directed.

Thus it is with the ignition current. It can "tickle," rather
viciously, sometimes, as many persons will aver, but the _amount_
of electricity involved is so slight as to render the high pressure
harmless. Nevertheless, it is well to avoid allowing the fingers or the
arm to become a part of the high-tension circuit, for the result may be
startling as well as annoying.

But in order that the high voltage shall be induced in the secondary
coil, the primary circuit must be alternately made and broken between
one stroke and the next. Consequently proper "piling up," or "surging,"
of the current will be effected. This is accomplished by means of an
"interrupter" that either vibrates rapidly or "snaps" once at the
formation of each spark. The former is the more common type used with
battery ignition and is known as a vibrating coil. A circuit breaker is
generally incorporated in the mechanism of a magneto, and consequently
when such an instrument is used, the vibrator on the coil is dispensed
with. It is the vibrator on each coil that forms the "buzz" that can
be heard whenever the box cover is removed, and that often furnishes a
simple test for determining the condition of the ignition system of the
particular cylinder with which that coil is connected.

The vibrator is a flat, spring steel piece that rests near one end of
the soft iron core around which the primary coil is wound. The springy
nature of the vibrator ordinarily holds it against a small, adjustable
contact point that should be set about an eighth of an inch from the
end of the above-mentioned soft iron core. The primary coil is so wired
that its current passes through the vibrator steel and the contact
point against which it rests. As soon as the current travels through
the coil surrounding the soft iron core, however, the latter becomes
magnetized and draws the steel vibrator toward it. This breaks the
circuit, the magnetism of the iron core disappears, and the vibrator
returns to its original position against its contact point. But this
action again forms the circuit, and the same operation is repeated as
long as the current is allowed to flow toward the coil.

This is the same principle on which an electric bell is rung, but the
vibrator of the coil makes and breaks the circuit much more rapidly
on account of the less weight of the moving parts. This vibration of
the coil interrupter is so rapid--hundreds a second probably--that the
resulting spark is practically continuous and shows no effect of the
breaks in the circuit.

Even though it is the primary current, of low voltage, that is
interrupted by the vibrator, the frequency of these interruptions
causes a slight sparking, or arcing, at the contact points. These are
therefore subjected to rather a high degree of heat, as well as a large
amount of wear, and it is necessary that they be made of a material
that will resist both. Platinum has been found to be unusually suitable
for this purpose, but owing to its high cost, only a small amount in
the form of two points, or "buttons," is used. One of these points is
placed in the vibrator steel, and the other is embedded in the end of
the screw against which the first rests. Thus the actual contact is
made against these heat-and-wear-resisting platinum points, and it is
evident that upon their proper action depends the formation of the
spark in the cylinder with which that particular vibrator is connected.

Notwithstanding the fact that platinum possesses high heat-resisting
properties, the constant arcing at the contact points will eventually
form a sort of corrosion in which minute particles of the material
are carried from one point to the other in the direction in which the
current flows. If the current is reversed, the corrosion will take
place in the other direction, and consequently the platinum point
that formerly lost a part of its material will gradually be "built up"
again. This corrosive action is known as "pitting," and while it may be
reduced to a certain extent by reversing the terminals of the battery,
as described, the platinum will occasionally require additional
attention.

A coil having badly pitted contact points on the vibrator will "stick"
and will cease to form a spark regularly. It is often difficult to
distinguish between trouble arising from badly-pitted contact points
and that caused by weak or nearly-exhausted batteries, as either
ailment produces the same symptoms of irregular running and "jerking"
in the motor. For this reason, a volt and ampere meter for measuring
the pressure and amount of the current delivered by the batteries
should form a part of every automobile owner's tool equipment.

It is the amperage, rather than the voltage, that is reduced through
continued use of the batteries, and when this quantity falls below
nine or ten, the cells should be discarded--or recharged, in the case
of a storage battery. But if the ignition occurs irregularly when the
batteries are delivering the proper amount of current, it is probable
that the trouble lies in the pitted condition of the platinum contact
points of the vibrator of the coil. Fine emery cloth rubbed over the
surfaces of contact should serve to remedy matters. It should be made
certain that the resulting surfaces on the platinum points are not only
rubbed smooth, but level, as well, in order that the entire area of
each will rest in contact and the current will not be concentrated at a
small portion.

It is probable that there will be a screw adjustment on the vibrator
by means of which the force with which the latter rests against its
contact point may be regulated. If the vibrator is set too tight, an
undue amount of current will be required to magnetize the core of the
coil sufficiently to pull the vibrator away from its contact point, and
the batteries will soon "run out." On the other hand, the tension of
the vibrator should be sufficient to enable it to spring away from the
core of the coil as soon as the circuit is broken, for otherwise the
vibrator will lag and will not be as "lively" as is necessary to obtain
the best results.

The contact screw should be set so that the vibrator rests _about_
three-thirty-seconds of an inch from the end of the magnetic core.
After the tension of the vibrator has been set to approximately the
proper amount, the ear must be trusted for the correct adjustment of
the contact screw. When the switch is thrown on and the motor turned
until current flows through the coil, the resulting buzz emanating
from the vibrator should be decided and forceful. If this buzz is
exceedingly high-pitched, it is an indication that the vibrator has
been set too tight, and its tension should be loosened if unscrewing
the contact point slightly does not lower the tone. It must be
remembered that the tension of the vibrator can be changed by turning
the contact screw. If this screw is turned down so that it forces the
vibrator toward the iron core, the tension will be greater than will be
the case if the contact point is turned to the left.

If the buzz of the vibrator is pitched lower than was formerly the
case, it is an indication that the contact point should be screwed
down, or that the tension of the vibrator should be tightened. It is
probable that turning the contact screw to the right will produce the
proper result. While these changes in the position of the contact
screw are being made, the switch should be left turned on so that the
variations in the pitch of the vibrator buzz may be detected. When an
evenly-pitched, vigorous buzz has been secured, the switch should be
thrown on and off several times to make certain that the response of
the vibrator is instant and positive. The switch should then be left on
and the vibrator allowed to buzz for several seconds in order that it
may be determined whether the pitch of the sound will change, or not.
If there is a change noticeable, the contact screw should be readjusted
until the pitch of the buzz remains constant as long as the circuit is
closed.

The coil and batteries or magneto by no means form the entire ignition
system, although the generation of the spark depends entirely upon
them. The spark must be regulated to occur at the proper point in the
stroke of the piston, as a continuous spark would not only waste the
current, but would cause the ignition of the charge during the upward
stroke and would result in an impulse in the reverse direction that
would prevent the motor from running for more than half a turn.

The device by which the time of the occurrence of the spark is
regulated is called the timer. This consists, in its essentials, of a
hard rubber disc provided with a copper or brass segment. A metal pin,
roller, or ball rests against the outer edge of the disc, and as the
latter is revolved, the electrical circuit is completed whenever the
two metal portions come in contact with each other. The hard rubber
being a non-conductor of electricity, prevents the flow of the current
at all other times. The disc of the timer, known as the "commutator,"
is so geared that it revolves in unison with the motor.

Inasmuch as the explosion occurs in each cylinder only at every second
stroke of a four-cycle motor, the commutator on this type of engine
is geared to revolve at one-half the speed of the crank shaft. In
the two-cycle motor, on the other hand, the explosion occurs in each
cylinder at every revolution, and consequently the commutator should
turn at crank shaft speed.

Although the spark is intended to occur approximately at the extreme
upper end of the compression stroke, a few degrees variation both above
and below this point is necessary in order to obtain the desired speed
and power flexibility of the gasoline motor. At high speeds, the spark
should be timed to occur before the piston reaches the extreme top
of its stroke, while at slower revolutions of the motor the ignition
should take place, in some instances, just after the piston has
started to descend. This variation In timing is obtained by swinging
the contact piece of the timer--known as the brush--either forward
or backward through an arc corresponding to the range of advance and
retard.

If this brush is swung in a direction opposite to that of the
revolution of the commutator, the metal portions will meet sooner, with
the result that the spark will occur earlier, or will be "advanced."
If, however, the brush is swung to a point farther along in the
direction of rotation of the commutator, the spark will occur later,
or will be "retarded." These variations of position of the brush are
generally obtained by means of a lever attached to the steering post or
wheel.

It is evident that the current must pass from the brush to the metal
segment of the commutator in order to complete the circuit through
the timer and thus form the spark. It is the primary current, or
low-tension current from the battery or magneto, that passes through
the timer, and as this is of low voltage and is therefore easily
discouraged, it is necessary that the contact points be kept clean in
order that its travel may be made easy. Timers are generally protected
from dirt, but the particles that will naturally be worn off from the
metal and rubber commutator and brush should be cleaned out before its
accumulation becomes deposited on the contact points and interferes
with perfect electrical connection.

A few years ago, the majority of battery ignition systems employed a
separate coil for each cylinder of the motor. Each coil in this system
is connected with an individual brush that operates against the same
commutator as do the brushes for the other cylinders. With such a
system, the primary circuit leads from one terminal of the battery to
the primary winding of the coil, through this and the vibrator to the
brush of the timer reserved for that particular coil and cylinder, and
thence through the switch to the other terminal of the battery. This
order may be reversed, or the timer, switch, and coil may be placed
in any consecutive position, provided the current passes through all
in its travel from one terminal of the battery to the other. The
secondary, or high-tension current is led from the terminal of the
secondary winding on the coil to the spark plug of the proper cylinder.
There should be a "ground" wire to serve for the return of the
secondary current. This may lead from any part of the primary circuit
to a clean metal connection on the motor.

The multiple coil system is still used to a large extent, but an
elaboration of it will be found on many of the modern cars. This
consists of the use of but a single coil for all of the cylinders of
the motor. This is done by means of a distributor, which is a sort of
"glorified timer" consisting of a commutator provided with as many
segments as there are cylinders in the motor. This distributor receives
the current from a single coil and delivers it to the proper cylinder
as the various connections are made. The timer still performs its
function of completing the circuit from the source of current only at
the proper instant, and leaves the distributor to serve the purpose of
a "switch" to "sidetrack" the current and deliver it at the various
cylinders in turn.

If it should ever become necessary to remove any part of the timer,
or to change the length of the spark control rods, the greatest care
should be taken to make certain that the motor is properly timed when
the various portions are replaced. This can best be done by setting the
spark lever in its central position, removing a plug from one of the
cylinders, and introducing a rod or long screw driver into the opening
for the purpose of determining the exact top of the stroke of the
piston. When the flywheel is turned, the top of the stroke should be
marked on the rod or screw driver as the latter is forced upward by the
piston.

If the spark plug is laid with its large nut resting on the cylinder
head, and the switch is thrown, the time of the occurrence of the spark
can be readily observed as the motor is turned slowly by hand. This
spark should occur in this particular plug just as the piston of that
cylinder reaches the top of its stroke, as indicated by the change in
the direction of the movement of the rod or screw driver. If the spark
occurs too soon or too late, the commutator should be moved backward or
forward to remedy the respective trouble. Although if the timer is set
properly for one cylinder it is probable that the spark in the others
is also timed correctly, it is well to test each to make certain that
there has been no uneven wear in the contact segments of the commutator
or the brush.




CHAPTER V

MAGNETOS


The perfection of the magneto and its application to cars of all
classes and sizes has marked the most important step in gasoline motor
ignition since the introduction of the electric spark. The magneto is
now considered one of the most vital parts of the car, and while it is
possible for the motor to be run for many miles on the batteries that
form the auxiliary ignition sources, the mechanical current generator
has left the field of the desirable accessories and has become an
actual, physical portion of the engine.

The operation of the magneto is simple, its whys and wherefores are
logical, and if one investigates the subject, even superficially, he
will discover that the much-maligned machine seldom gives trouble,
and that when it does, such action, or failure to act, is due to
neglect, abuse, or some other perfectly legitimate reason, rather than
"pure cussedness" on the part of the instrument itself. If the mere
mechanical aspect is considered; if it is realized that the magneto
consists mainly of a bundle of wires which, when revolved near the ends
of a magnet, collects that magnetism and sends it through the circuit
in the form of the electric current, and that consequently the magneto
is a converter that changes part of the mechanical energy of the motor
into the spark-forming fluid, the chief idea of magneto principles may
be more easily grasped.

To be sure, the magneto is delicate, and for that reason it should
never be dissected by the amateur, but inasmuch as what few adjustments
it has are readily accessible, it is seldom that the machine need to
be taken apart. The platinum points of the contact breaker, usually
located in the small box on the end of the armature shaft, may need to
be smoothed with emery paper occasionally if they have become pitted
from excessive sparking, but this is a simple operation and is not
greatly different from the care given to the vibrator of the dashboard
spark coil, as described in the preceding chapter.

A few drops of oil should be fed to the lubricating cups or holes of
the armature shaft as often as the directions call for--usually about
once every five hundred miles--but aside from this, the owner can
generally forget that he has a magneto, and will only be reminded of
the fact by the pleasing absence of ignition trouble. If ignition
trouble does occur, it is more than probable that the fault lies with
the plugs, timer, or wires, rather than with the magneto.

The man who drives a magneto-equipped car knows that the current
producer is run by a gear connected, either directly or through the
medium of other gears with the crank shaft of the motor. He knows,
then, that the magneto is driven positively and that there is a
constant relation between its speed and the number of revolutions of
the motor.

But does he know that it is absolutely necessary that a certain
position of the armature shall always correspond with a similar
position of the crank shaft of the motor, and that consequently
the same teeth of the driving gears must always mesh? He will most
assuredly be made aware of this if he disconnects his magneto and
then fails to replace the gears so that exactly the same teeth are in
mesh, for even the difference of a single tooth between the normal
positions of the armature and crank shaft will prevent the magneto from
delivering a sufficient spark to enable the motor to run.

The reason for this is simple. All of these direct-driven magnetos
are of the alternating current type, as this form allows of the
simplest construction of armature and windings. The alternating
current generator obtains its name from the fact that there are no
regularly-defined north and south poles at any part of the circuit, as
these keep changing continuously, or alternating.

During each revolution of the armature of the alternating current
magneto, there are but two positions at which a current will be formed.
Now the spark in any cylinder of a motor is required at about the top
of the compression stroke of the piston in that cylinder. Consequently
when the piston is at the top of its compression stroke, ready for
the spark that will ignite the charge, the armature of the magneto
must be in one of its two current-generating positions, and there must
therefore be a constant relation between the position of the crank
shaft, to which each piston is connected, and that of the revolving
part of the magneto.

If, now, the driving gear of the magneto is returned to its place
without regard to the teeth of the next gear with which it meshes, it
will be seen that the proper relation between the position of the
armature and that of the crank shaft will not be maintained. Under
these conditions, when the piston is at the top of the compression
stroke, ready for the spark, the armature will not be in a position
at which a current can be generated, and there can consequently be
no spark formed at the plug. Conversely, when the armature has been
revolved to the position at which a current will be formed, none of the
pistons will be requiring the spark, and this consequent lack of "team
work" will prevent the operation of the motor.

In order to maintain this team work between the armature of the magneto
and the crank shaft of the motor, the intermeshing teeth of the gears
should be marked with a prick punch before they are removed, so that
they may be returned to their proper place without trouble. Only in
this manner can accurate results be obtained, if it is at any time
necessary to remove all or part of the magneto driving gear.

The magnets forming the "fields" of the magneto in which the armature
revolves are of the permanent kind; that is, they do not depend upon
windings and a separate electric current for their excitation, as
is the case with some of the larger generators. These magnets may
be considered to be the most faithful part of the machine, for they
generally retain their strength under all conditions of rest or work,
and it is upon them that the proper operation of the magneto largely
depends.

A magneto in which the magnets have become weakened is useless for
ignition purposes until the fields can be remagnetized, and as this
can only be done at the factory, the machine in its entirety must be
removed from the motor. It is a comparatively easy matter to determine
whether or not the fields have lost their magnetism by placing a
piece of iron or steel within close range of the base or sides of the
magneto. An appreciable pull will be exerted by the magnets if they
still retain their strength, although it is not to be supposed that the
force thus exhibited will be very vigorous from such a small machine.

If the magneto has been disconnected from its driving gear for any
reason, the amount of magnetism remaining in the fields will be best
determined by turning the armature shaft with the hand. A resistance
should be offered to the turning at first until a certain point is
reached, after which the armature should exhibit a strong tendency to
fly forward to a new position, one hundred and eighty degrees beyond
its former normal position of rest. This activity of the armature is
one of the best guides to the amount of magnetism remaining in the
fields.

Many magnetos that have been installed on old motor cars not
previously so equipped are of the friction-driven, direct-current type
that produces a uniform spark at any point throughout the armature
revolution. Current from these may be used to charge a storage battery
for the operation of electric lights or to supply auxiliary ignition
current for starting. The positively-driven, alternating-current
magneto may also be used to operate electric lights on the car, but
this type of current cannot be stored in a battery, and consequently
the lights are available only when the motor is running. The magneto,
however, is not primarily an electric-lighting outfit, and unless it is
especially designed for the double purpose, a separate machine should
generally be used for supplying illuminating current.




CHAPTER VI

CARBURETORS AND THEIR FUEL


Although gasoline is inflammable in its liquid state, its combustion
is not sufficiently rapid to approach the _explosive_ point necessary
to render its energy available in the automobile engine cylinder. The
proper proportion of gasoline _vapor_ and air, however, forms a mixture
that is highly inflammable and that will be entirely consumed in the
engine cylinder under ordinary conditions within about one-twentieth
of a second after the formation of the spark. This rapid combustion
so nearly approaches the instantaneous action of an explosion that it
may be considered as such in all ordinary discussions of the gasoline
engine. Literally, however, the gasoline engine is not an _explosion_
motor, but rather is it an engine of the _internal combustion_ type. To
obtain this gasoline vapor in an easily-controlled form the carburetor
was designed as one of the most important adjuncts of the automobile.

The first form of carburetors, or "vaporizers," as they were called
then, employed a flat, woven lamp wick over which the gasoline flowed.
This spread the fuel out over a comparatively large surface and
rendered evaporation rapid and simple. The chamber containing this
wick was placed in the line of the intake pipe of the motor and was
connected with the cylinders on the descent of the pistons on the
suction stroke through the medium of the various inlet valves. In
a four-cycle motor, the piston acts as a suction pump on alternate
down-strokes and serves to draw the charge into the cylinder. This
suction created the necessary current of air to facilitate evaporation
of the gasoline on the wick, and by regulating the size of the
passages, the proper proportion of air and gasoline vapor could be
obtained.

The modern, high-speed automobile motor, with its varying demands upon
the carburetor, created the necessity for a more delicate, flexible,
and compact vaporizer than was to be found in the "lamp wick" type.
Consequently the wick was replaced by a small, slender, hollow tube
having a cone-shaped opening at its upper end through which the
gasoline from the feed pipe was made to pass. Fitting into the upper
end of this tube, and pointed to the same angle, was a cone-shaped
"needle" that could be moved in and out of the opening. If this needle
was unscrewed slightly so that it did not form a tight fit with the end
of the tube, a small ring would be formed through which the gasoline
must pass when sucked by the alternate down strokes of the pistons.
This tube and needle constitute, under various guises, the "needle
valve" with which practically every modern carburetor is equipped.

When the gasoline, rushing through the small tube, strikes the
restricted opening of the needle valve, it is broken up into a fine
spray which, under proper conditions, will become vaporized almost as
soon as it comes in contact with a current of air. This air current is
induced by the same pump-like effect of the pistons as that which sucks
the gasoline through the needle valve, and thus it occurs only when the
charge is desired in the cylinders.

But the carburetor is not merely to provide a compact device for
vaporizing the gasoline, for it must also furnish a means of regulating
the proportion of gas to air. Gasoline vapor is only highly inflammable
when mixed with the proper quantity of air, and if this proportion is
varied above one limit or below another, ignition of the charge will
not occur in the cylinders. In fact, the allowable variation in the
proportion of gasoline vapor to air is restricted between very narrow
limits, and should not change more than four or five per cent. from
one extreme to the other. The proportion of gasoline vapor to air by
weight is about one to eleven, although this will vary somewhat with
the different grades of fuels.

The point to be emphasized, however, is the fact that the proper
proportion of air to gasoline vapor, however it may vary with different
grades, should be kept constant at all speeds of the motor whenever
that particular grade of fuel is used. By volume, about 97½ per
cent. of the mixture should be air and the remainder gasoline vapor,
and it is the device that will the most nearly maintain this proportion
under all conditions of speed, temperature, and air pressure that will
prove to be the most delicate and flexible carburetor.

A carburetor may be adjusted for different motors, or for different
operating conditions of the same motor, by means of the needle valve.
The farther end of the slim rod on which the needle point is mounted
terminates in a thread and finger nut that projects through the shell
of the carburetor. By turning this nut in one direction, the needle
valve is screwed up toward the cone-shaped end of the tube and the
orifice through which the gasoline may pass is thus reduced in size.
This will decrease the amount of gasoline sprayed into the air passage
and will consequently change the composition of the mixture. This,
however, should not be confused with throttling the motor. When the
needle valve is tightened, the volume of the mixture passing to the
cylinders is the same, for it is only the proportion of gasoline vapor
in that mixture that is changed.

Throttling consists in restricting the size of the opening through
which the _mixture_ passes, and thus limits the amount of the
charge that reaches the cylinders at each suction stroke of the
piston. Throttling is used to reduce the power--and consequently the
speed--developed by the motor, while a decrease in the amount of
gasoline supplied to the air through the needle valve may serve to
increase the power through an improvement in the nature of the mixture.

Since the gasoline vapor, by volume, forms only about three per cent.
of the explosive mixture admitted to the cylinders, a slight variation
in the size of the needle valve opening will result in a marked change
in the composition of the charge and may make all the difference
between poor and perfect running of the motor. Consequently the needle
valve nut should be moved but the small fraction of a turn for each
adjustment. A motor which may refuse absolutely to run at one position
of the needle valve may give perfect results if the nut is unscrewed
but the eighth of a turn.

In view of the marked difference in the results obtained from the use
of mixtures that are "just right," and those which vary but a slight
percentage in the proportion of gasoline vapor to air, it may be well
to examine, superficially, the effects of "rich" and "weak" charges,
and therefrom to obtain a list of "symptoms" which may aid us to
diagnose motor trouble properly.

We all know that air--or oxygen--is required to support combustion.
"Snuffing" a candle is merely covering its end so that air cannot reach
the flame. For the same reason, gasoline in a covered tank cannot burn,
no matter how great the heat applied to it. The heat of the electric
spark in the cylinder, although intense, does not cover a sufficiently
large area to ignite any charge except that composed of the proper
proportion of gasoline vapor and air. If there is too much gasoline
vapor, making a "rich" mixture, there will not be sufficient air in
the charge to support the entire combustion of the gas, and the burning
will be slow--if it takes place at all. The same conditions will
prevail if there is an insufficient supply of air for a given quantity
of gasoline vapor, and consequently a rich mixture may be obtained
by reducing the air flow as well as by adding to the amount of gas
admitted to the mixing chamber.

A rich mixture will cause irregular explosions in the cylinders, and
will often emit a black, pungent smoke at the exhaust. The motor will
probably overheat easily, due to the slow-burning properties of the
mixture and the resulting fact that a large portion of the cylinder
walls uncovered by the pistons will be exposed to the flame. In some
instances, the cylinders will miss fire at regular intervals, thus
changing the synchronism of the impulses with a well-defined and
periodic "skip" in the sound of the explosions.

While these are by no means certain symptoms of a rich mixture,
the first test to be made should be to tighten the needle valve
adjustment slightly when the motor is running and to note any resulting
improvement in the regularity of the explosions. It may sometimes be
difficult to distinguish between the symptoms of a rich and a weak
mixture, but the readjustment of the needle valve as just described
will at least serve to locate the trouble or to eliminate one or the
other possibility from consideration.

When a mixture is "starved", or when there is an insufficient supply
of gasoline vapor to unite with the air admitted to the cylinders, the
charge will not be highly inflammable and may not be ignited by the
small spark formed at the plug. Even when ignition does take place, the
resulting power impulse will be weak because of the comparatively small
amount of pressure-producing gas in the mixture. The explosions may
occur regularly for a while, but there will be a marked decrease in the
power developed by the motor, and owing to the fact that weak mixtures
may be slow-burning, "back-firing" will often result in some engines to
which such a charge has been fed.

On the other hand, if a motor will run at all on a weak mixture, it
will produce better results than would be the case were the charge
too rich in gasoline vapor. Consequently the needle valve should be
closed as much as is consistent with smooth running of the motor, but
the moment a loss of power or irregular explosions occur, the mixture
should be enriched.

At low speeds of the motor, the pumping action of the pistons is not as
great as is the case at high revolutions, and consequently the suction
drawing the gasoline through the needle valve is diminished. For this
reason, the needle valve opening must be made larger or the air passage
restricted for slow speeds of the motor, and it was consequently
necessary, on the old, non-automatic vaporizers, to _increase_ the
gasoline supply whenever the revolutions of the motor were to be
reduced. The modern carburetor is sufficiently automatic in its action
to provide the proper mixture within wide ranges of speed change of the
motor, but even nowadays it is often found necessary to increase the
gasoline supply or to reduce the amount of air admitted to the intake
pipe whenever it is desired to throttle the motor down to a very low
number of revolutions per minute.

The automatic action of the ordinary carburetor is obtained by
increasing the air supply at higher speeds of the motor. Consequently
the motorist will realize that whenever the needle valve is to be set,
such regulation should be made when the motor is well throttled, for
if an ample gasoline supply is obtained at low speeds, the mixture
will certainly be sufficiently rich at increased revolutions. If, on
the other hand, the carburetor should be set to supply a proper mixture
at high speeds, the mixture would be impoverished when the motor is
throttled, and irregular running would result.

The air for the operation of the motor at ordinary speeds is supplied
through a fixed opening in the carburetor connected with the chamber
into which the gasoline spray is introduced. In addition to this, most
carburetors are supplied with an "auxiliary air opening" which serves
to furnish the additional air necessary for the mixture at high speeds
of the motor. The fixed opening, being restricted in size, cannot
admit the increased quantity of air demanded by the higher speeds
of the motor. The auxiliary opening is provided with some form of
automatic valve which may consist either of a series of ball "checks,"
a spring-actuated "mushroom valve," or a series of special valves, each
of which opens at successively increased speeds of the motor.

All of these devices operate on the same principle, however, and
allow the increased suction of the motor to add to the size of the
air passage automatically--either by the farther opening of a
single valve, or by the successive opening of different valves. Some
carburetors are provided with an adjustment by means of which the
"delicacy," or ease of opening, of the auxiliary air valve may be
regulated. This may be done by means of a nut and screw which will
increase or decrease the tension of the controlling spring. If this
spring is set with a high tension, the auxiliary valve will act only
when the motor is exerting great suction, or at fast speeds.

The regulation of the auxiliary valve is an adjustment that should be
made only after the needle valve has been set properly for slow speeds
of the motor. When this condition is obtained, the throttle should be
opened and the further adjustment of the carburetor for high speeds of
the motor should then be made through the auxiliary air valve. In other
words, the needle valve should be set so that the motor runs properly
at low speeds, while the adjustment of the auxiliary air valve should
be made only to secure smooth operation at a high number of revolutions.

It is not to be understood that less gasoline is actually required at
high speeds of the motor because the supply often needs to be cut down
at the needle valve under these conditions. The actual amount required
at high speeds is, of course, greater than is the case at slow, on
account of the greater number of explosions in the former instance. But
the suction of the motor generally increases the gasoline flow beyond
the demands of the cylinders at high speeds, and it is for this reason
that the automatic auxiliary air supply is provided to furnish the
additional air required to support combustion. In fact, at heavy loads,
when the total amount of gasoline consumed must be great, a secondary
jet of fuel is brought into action in some carburetors. This is known
as the "multiple-jet" type and is found on some of the large engines
that must possess a speed and power variation between wide ranges. The
action of these various jets is entirely automatic and is dependent
upon the speed and fuel requirements of the motor.

Were the gasoline fed directly from the fuel tank to the needle valve
of the carburetor it is evident that the rate of flow of the liquid
would depend, to a large extent, upon the amount in the tank and upon
the position of the car. This would cause each charge to differ in the
proportion of gasoline vapor to air, and it is hardly probable that the
motor could be run at all under such conditions. In order that the
pistons may suck the gasoline from a level that does not vary with
the amount of fuel in the tank or the position of the car, a separate
compartment is provided in the carburetor. This is known as the "float
chamber," and it is from this compartment that the gasoline passes
through the needle valve into the vaporizing or mixing chamber.

A cork or hollow metal float is placed in this float chamber and is
mounted on a lever connected with a valve located at the end of the
gasoline feed pipe. As the gasoline is admitted to the chamber, the
float rises and closes the valve controlling the flow of fuel. As the
gasoline is sucked through the needle valve from the float chamber,
the float in the latter lowers, and the fuel is again admitted by
the opening of the above-described valve. The float and valve are
exceedingly delicate in their operation and the gasoline is thus kept
at a constant level in the chamber under all conditions of the car and
tank.

The stem upon which the float of some carburetors is mounted is
sometimes threaded and provided with a nut by means of which the float
may be raised or lowered. This furnishes an adjustment for varying the
level in the float chamber and determining at what point the flow
of gasoline shall be cut off by the automatic valve. The float is
supposedly properly regulated when the carburetor leaves the factory,
but the stem may become bent or the carburetor may be applied to a
motor other than that for which it was originally designed. In either
of these events, it may be found necessary to raise or lower the float
before the proper level of gasoline can be maintained in the chamber.

If the float is too high on its stem, the gasoline control valve may
not be operated until the fuel overflows in its chamber. This is known
as a "flooded" carburetor and produces a rich mixture which will
ultimately prevent the proper operation of the motor. Turning down
the gasoline supply at the needle valve will not remedy this, for the
fuel will reach the vaporizing chamber by another route. A flooded
carburetor often gives trouble, and while it may be remedied easily,
the amateur may experience difficulty in locating its source.

As soon as it is discovered that a carburetor has become flooded, the
needle valve should be tightened so that no gasoline can pass through
it, and the motor should then be cranked. This will serve to evaporate
the excess gasoline in the float chamber and reduce the level to the
point at which it will not overflow. The exact number of turns and
fractions of turns through which the needle valve nut was moved should
have been noted in order that the valve may be reset to its original
position after the surplus fuel has been "cranked out."

A float that is set too low on its stem will close the fuel supply
valve before a sufficient amount of the fuel has flowed into the
chamber, and will form a "lean" mixture at high speeds of the
motor--even though the needle valve should be opened wide. The obvious
remedy for such a condition is to raise the float until the gasoline
will be maintained at the proper level. If there is no nut and screw
adjustment by which the float may be raised, the arm to which it is
attached, and which is connected with the valve, may be bent slightly.

But the motorist should not "jump at conclusions" and assume that the
float is improperly set the moment the carburetor begins to flood or
the motor appears to "starve" at high speed. The first condition may be
caused by a piece of dirt or other foreign matter that may have become
lodged on the valve seat and prevented the valve from closing when
the gasoline reached the proper level in the float chamber. This will
produce exactly the same results as will a high float and is a trouble
that will more often occur in the average carburetor.

The difficulty may generally be remedied easily by draining the
gasoline from the float chamber after the valve in the main supply
pipe has been turned off. The offending foreign matter will generally
be carried with the gasoline as the latter is drained, and the valve
in the feed pipe may again be opened as soon as the drain cock is
shut off. If this fails to remedy matters, it is probable that the
difficulty lies with the float.

A clogged gasoline pipe or dirty strainer will produce the same effect
on the operation of the motor as will a float that is set too low on
its stem. When the motor seems to starve at high speed, and it is
evident that there is sufficient gasoline in the tank, the union should
be disconnected at the point where the feed pipe joins the carburetor.
If there appears to be an ample flow through this pipe when the main
valve is opened, it is probable that the stoppage has occurred in the
strainer. If the flow through the main feed pipe is not free, however,
it is possible that the vent hole in the filler cap on the tank has
become stopped or that the latter has been screwed down too tightly. In
the gravity feed systems, some method must be provided to allow the air
to flow into the tank to replace the gasoline fed to the carburetor. If
there is no hole in the filler cap, the latter should not be screwed
down so tightly that an airtight joint will be formed.

Probably the simplest method of determining whether the trouble lies
in a low float is to prime the carburetor and to observe the ease with
which this can be done and its effect upon the engine. Nearly every
carburetor is provided with a "flushing" or "priming" pin by means of
which the float can be depressed so that the gasoline chamber will
be filled rapidly to a point above its normal level. This is useful
in starting, as the desired rich mixture is quickly obtained without
an undue amount of cranking. If the carburetor flushes easily, it
is evident that there is no serious stoppage in the pipe. If this
easy flushing is followed by good running on the part of the motor,
and if this, in turn, is succeeded by gradually-diminishing impulses
indicating a weakening mixture, it is quite evident that the float is
preventing the flow of the gasoline at the proper time.

In addition to the flush pin found on carburetors, many are provided
with other devices to render starting easy. It is well known that a
"high-test" gasoline, such as a 76, will vaporize more easily than will
one of a lower degree of specific gravity. Also, every motorist has
had impressed upon him the fact that heat aids in the vaporization of
gasoline. If we try to start a motor on a cold morning with a low-grade
gasoline, such as the 60- or 62-degree fuel now generally obtained, we
know that a rag dipped in hot water and wound around the carburetor
will help matters.

To enable low grades of fuel to be properly vaporized under all
running conditions, many carburetors are provided with a water jacket
surrounding the vaporizing chamber. This jacket is connected with the
cooling system of the motor, and the hot water surrounding the chamber
so warms the interior that vaporization is greatly facilitated. Some of
these systems are provided with a shut-off cock by means of which the
carburetor may be operated with hot water in the jackets, or not, as
desired.

Other carburetors employ a jacket surrounding the exhaust pipe of the
motor and connected with the vaporizing chamber. The air is heated by
the hot exhaust pipe as it is sucked into the carburetor, and this also
facilitates the vaporization of the fuel. Some carburetors are provided
with both jacket systems, while others have neither, but whatever
design is installed, the best results will be obtained if cold air is
used after the motor is once started. Cold air is more "concentrated"
and contains a greater amount of oxygen per cubic foot than does air
that has been expanded by heat, and consequently many carburetors are
provided with a means of turning off the hot air after the motor is
started.

The higher the degree of specific gravity of a fuel on the Baumè scale,
the more volatile will it be, and consequently a 68° gasoline will
vaporize more easily and give more power than will a 60° or 62° fuel.
72° gasoline is often used in races, but the average motorist does
not get better than 64°--and he is sometimes lucky to obtain fuel of
that specific gravity. A hydrometer, or specific gravity tester, is a
convenient instrument for the average motorist to own, and with it he
may tell exactly what grade of fuel he is paying for. The Baumè scale,
by which all gasoline is tested, reads in degrees, and the specific
gravity is obtained by observing the depth to which the hydrometer
sinks in the liquid. This instrument resembles somewhat a glass
thermometer, and is so graduated that the deeper it sinks in a liquid,
the higher will be the reading on its scale.

Water in the fuel is an annoyance that is often encountered by the
automobilist and the motor boatman, and this will make its presence
known by causing the motor to skip when all adjustments and connections
seem to be in perfect condition. Water is much heavier than gasoline
and has no affinity for it, and consequently, as it sinks to the
bottom of the tank, a few drops in a large amount of gasoline will
cause trouble by passing out through the needle valve at intermittent
intervals and forming an unexplosive mixture.

The presence of the water in the fuel may be detected easily without
the use of a hydrometer by drawing some gasoline from the bottom of
the tank into a tin or white-enameled cup. If water is present, it may
be seen in the form of small globules in the bottom of the cup. If the
contents of the cup are poured over a flat surface so that the liquid
may be allowed to spread, the gasoline will be seen to cover a large
surface and evaporate quickly, while the water will seem to remain
in the globules unevaporated for some time after the gasoline has
disappeared. This latter test will sometimes show the presence of water
when none can be discerned in the bottom of the cup before the contents
are poured out on the flat surface.

The practice of "doping" the fuel tank by adding to the gasoline ether
or some other highly volatile liquid is not to be recommended to the
average motorist. A few ounces of ether or chloroform added to the fuel
will form a more volatile and consequently more powerful mixture, but
unless the greatest care is taken, the motor is liable to be completely
ruined by such a procedure. Numerous cases are on record in which
cylinder heads have been blown off or castings cracked by the force of
some of the explosions when too much "dope" has found its way into the
mixture.

Although the average motor gasoline obtainable nowadays is hardly all
that could be desired as automobile fuel, a little care taken when
filling the tank will eliminate many of the carburetor annoyances to
which many cars seem to be subject. The cap of the tank should never
be taken off when the air is filled with particles of dust that are
liable to find their way into the fuel, and care should be taken to
see that no pieces of the rubber or leather washer or packing drop into
the gasoline when the cap is removed. Foreign matter and water that may
be in the gasoline when purchased may be removed by straining the fuel
through a chamois skin placed inside of the funnel through which the
tank is filled.




CHAPTER VII

LUBRICATION


A lubricant acts as a sort of pacifier between two surfaces that
would otherwise move in contact with each other. No surface can move
in direct contact with another of the same or a different material
without the generation of heat; but the amount of heat generated, or
resistance met with, is determined by the nature of these two rubbing
surfaces. The oil, or grease, or whatever suave, slippery substance is
to be used as a lubricant, interposes itself in a thin film between
the two rubbing surfaces and smooths matters over, as it were. If a
sufficient amount of this mechanical soothing syrup is not fed to the
rubbing surfaces, the temper and temperature of each will be raised to
the point where they will "clinch," and much time and effort may be
required before harmony can again be restored.

Thus it is actually upon a film of lubricant that a shaft rests, rather
than upon the bearing, or "box," in which it turns. If the bearing
is set so tight that there is no room for the interposition of an oil
film, the shaft and journal will at once heat. The greater the pressure
of the shaft in its box, the thicker, or heavier, should be the
lubricant used, for a light oil would be squeezed out or "broken down"
more easily than would one that possesses greater viscosity.

The "coefficient of friction" may be termed the mechanical "amount of
irritability" generated when two surfaces are rubbed together. Thus if
two metals are rubbed together, this figure is high, and a large amount
of friction, or heat, will be generated. A metal rubbing over oil,
however--as is the case with a well-lubricated bearing--will arouse but
little resentment and its pathway will be made smooth and easy, for the
coefficient of friction of these two materials is low. The lower this
figure can be kept, the more easily can the surfaces be rubbed over
each other and the higher will be the efficiency of the bearing.

Apply this to every bearing or rubbing surface of a motor, and we see
that proper lubrication affects not only the length of life of the
moving parts, but the ease with which the engine can be run and the
consequent power development. Thus, a lubricant that will prevent wear
between the moving parts may be supplied to the bearings and pistons of
a motor, and under this condition the engine might "last" indefinitely;
but this oil might be so viscous or possess so high a coefficient of
friction that each bearing would turn with difficulty and much effort
would be required to run the motor before it could begin to develop
power.

But the introduction of oil to a bearing not only reduces the
friction between the surfaces that would otherwise move in contact
with each other, but it serves another very important purpose. Every
properly-lubricated portion of a motor either moves in a bath of oil
or is connected with an oil reservoir so that a certain amount will
be fed regularly to the rubbing surfaces. There is always _some_ heat
generated in a bearing, no matter how well it may be lubricated, and
the continuous flow or circulation of the oil serves to carry off this
heat that would otherwise tend to dry the lubricant if there were no
fresh supply.

The proper lubrication of the motor is even more necessary than is the
adjustment of the carburetor or the condition of the ignition system.
To be sure, if either the carburetor or the ignition system is out
of order, the motor will not run, but no actual harm to the mechanism
will result from this fact. On the other hand, a motor may be run
indefinitely with a defective lubricating system, and no apparent harm
will result--until the end of that indefinite time arrives and it is
found that the machine is a fit subject for a junk heap.

Let us see how many parts of the motor are reached by the gallon or
so of oil that we pour into the tank. A six-cylinder motor may have
seven crank shaft bearings; it will certainly possess six connecting
rods, each of which will be provided with a bearing at both its large
and small ends--or twelve in all; there may be two cam shafts, each
with five bearings and half a dozen cams; these will require, together
with the magneto and pump shafts, five or six gears in the forward
train; and the six pistons will demand their share of attention
from the lubricating system. Here is a grand total of over fifty
rubbing surfaces on a large motor, and the oil must be thoroughly
and constantly distributed to each. Of course, many smaller motors,
provided with but a single cam shaft and a three-bearing crank shaft,
may possess but one-half of this number of lubricated parts, but at the
least, the oil must reach with unfailing certainty two dozen vital
places of the engine.

At some of these portions, the movement is comparatively slow and the
pressure is not great. Therefore such surfaces as the cams or valve
stem rollers will demand less oil than will the bearings revolving at
higher speed and carrying heavier loads. But it is the hardest-worked
bearings that form the majority of the friction surfaces of a motor,
as will be realized when it is remembered that all points on the
circumference of a three-inch crank shaft bearing will travel at the
approximate rate of 1,000 feet per minute--and these are the portions
that also carry the heaviest load.

But while the pistons can hardly be called bearings in the
generally-accepted layman's definition of the term, they require the
lion's share of the lubricant, and are the first portions of the motor
to feel--and show--the effect of any failure of the oiling system.
While in terms of miles per hour, the movement of the pistons may not
seem very rapid, the thousand feet per minute at which each ordinarily
travels is rather a high rate of speed when it is considered that it
is entirely a rubbing or a sliding motion, and that the direction
is reversed more than two thousand times during each sixty-second
period. This means that each piston slides or rubs within the cylinder
walls for a distance of between two and three thousand miles during
an ordinary season. And remember that this is not a rolling motion,
but a continuous rubbing! In addition to this high-speed rubbing, the
pistons are pressed firmly against the side of the cylinders on each
explosion stroke throughout a portion of their travel. This corresponds
to a heavy pressure carried by the rubbing surfaces, and is caused by
the side thrust induced by the angularity of the connecting rod as it
overcomes the resistance of the load through the crank shaft.

But this is only a small portion of the difficulties that must be
overcome in cylinder lubrication. Not only must the oil pacify the
rubbing surfaces and keep them well separated, but it must remain
within a restricted territory of the cylinder walls. Whatever oil
reaches the upper portion of the cylinder walls will be burned and will
contribute to the formation of the carbon that is the mortal enemy
of efficient running. Large quantities of oil burned in the cylinder
will also form the dense clouds of choking blue smoke that the health
authorities of many cities have been investigating, which have led
to the enactment of city ordinances making the driving of a smoking
automobile a misdemeanor.

In view of the difficulty which has been experienced by many drivers
in sufficiently lubricating the pistons without causing the car to
emit clouds of smoke, it may well be asked, "Why cannot an unburnable
oil be used and thereby eliminate this trouble?" This is out of the
question, for the mineral oils now used are obtained from petroleum
and are cousins of kerosene, gasoline, benzine, and many of the other
highly-inflammable liquids that need but the touch of a match to
burn almost with the rapidity of an explosion. But notwithstanding
the excitable family to which the mineral oils belong, the modern
motor car lubricants are removed a sufficient distance from their
more inflammable relatives to enable them to withstand a temperature
of between 400 and 500 degrees, Fahrenheit. This is sufficient
heat-resisting ability to enable the oil to stay on the cylinder walls
near the bottom of the stroke, where it is most needed; but even though
its burning point could be raised to a degree double its present
amount, it could not withstand the high temperature generated in the
top of the cylinder at the time of the explosion. The temperature
here reaches a point well above the 2000-degree mark, and were it not
for the cooling system, parts of the interior of the cylinder would
probably be melted by the continued application of this excessive heat.

_Any_ oil, consequently, would find but small opportunity to remain
in its normal state after it once reached a point at which it would
be exposed to the heat of the explosions, and we must look for a
preventive measure other than that of increasing the flash-point or
burning-point of the lubricant. But this high temperature does not
exist throughout the stroke, for as the piston descends and the gas
expands, heat is given off until the oil on the lower portions of
the cylinder uncovered by the piston is sometimes able to remain
in comparative peace. And even though this oil remaining on the
cylinder walls at the bottom of the stroke should be burned, it would
not be present in sufficient volume to create the dense clouds of
objectionable smoke. Consequently it is the endeavor of engineers so to
design the pistons and lubricating system that excess oil will not be
fed to the pistons and allowed to remain on the walls after the former
have descended.

But an excess amount of oil fed to the cylinders will result in so
much less harm than will an insufficient supply, that we are treading
on rather dangerous ground when we warn the amateur to cut down his
lubricant to the point where there will be no smoke. As there are no
ordinances that absolutely prohibit the slightest appearance of smoke
at the exhaust, and as a faint blue trail is an excellent indication
that the motor is receiving sufficient lubrication in the cylinders,
it forms a satisfactory test by which the novice can determine the
condition of the oiling system.

By the time that the exhaust gases have passed through the pipes
and have expanded in the muffler, some of the blue smoke may have
disappeared, and consequently the fact that a car does not give a
trace of vapor at its exhaust should not necessarily be taken as an
indication that the motor is not well lubricated. If the owner would
satisfy himself that the cylinders are receiving a sufficient amount of
oil, he may open the individual pet cock on each, and if he finds there
a faint blue trail of smoke at each explosion in that cylinder, he may
rest assured that harmony exists between the rubbing surfaces of the
piston and the cylinder walls.

With the increase in the size and power of the automobile motors and
the proportionately greater number of parts demanding lubrication,
the attention required from the driver by the oiling system has been
greatly lessened. Instead of the necessity of turning on individual oil
cups whenever the motor is started, the modern driver merely twirls
the starting crank or presses the button of the self-starter, secure
in the knowledge that whenever the motor runs, the lubricating system
operates--provided, of course, the reservoir is filled and there is
no stoppage in the pipes. The oiling system of the modern motor is
absolutely automatic, and if supplied with a sufficient quantity of a
good lubricant, it will perform its work with an absence of trouble
that places it among the greatest improvements of the engine of recent
years.

Individual oil cups such as were used formerly, have been eliminated
from the cylinders, and whatever sight-feeds there may be are placed
on the dash in plain view of the driver. Instead of relying upon
the suction of the cylinders for the positive feed to the piston,
mechanically-operated pumps are used to force the oil to the various
portions of the motor. In some systems, there is a separate pump for
each oil lead. This is known as a mechanical oiler, and generally
consists of an oil tank located on the dashboard of the car--either in
front of the driver, or under the motor hood--and connected by means of
a belt or gear with some shaft of the motor. The belt or gear drives
a shaft to which is connected the plungers of the various oil pumps
that force the oil to the different parts of the motor. Before passing
to the individual pipe, however, the oil drops through a sight-feed
connected with that lead, and as all of these sight-feeds are mounted
in a row within plain view of the driver, the condition of the
lubricating system in part or in whole may be determined at a glance.

The parts of the motor that are lubricated by an independent feed line
in this manner may vary with different motors. In general, however,
it may be said that it is seldom that the oil is fed directly to the
piston, but that the lubricant is first distributed to the oil wells in
the crank case. Here, the splash of the cranks as they revolve in the
oil is depended upon to throw the lubricant upon the exposed portion of
the piston as it reciprocates below the cylinder walls. The sides of
the piston thus covered carry the oil to the cylinder walls.

It is evident that if an excess amount of oil is continually carried
up by the piston to the cylinder walls, a certain proportion of this
lubricant will reach the open space in which the charge is ignited,
and will there be burned--with the attendant formation of clouds of
objectionable smoke. This trouble is overcome to a certain extent
in some motors by the use of a type of ring set in the piston that
prevents the lubricant from passing to the upper portion of the
cylinder; but all the oil cannot thus be retained, and it therefore
behooves the driver not to allow too great a quantity to be fed to the
crank case if the "splash" system is used.

The main bearings on which the crank shaft revolves are generally
supplied with oil by independent leads from the oiler, and when the
above-described system is used they may be regulated independently of
the splash feed lubricating pipes. Excess oil at the bearings will
cause no damage, but each crank shaft journal does not demand as great
an amount as that supplied to a piston and connecting rod bearing.

Many lubricating systems that are now in popular use employ but one
pump to force the oil to the various bearings and rubbing surfaces,
and regulate the supply by the size of the pipe leading to each. A
satisfactory method of overcoming the possibility of excess oil in
the cylinder has been adopted by some manufacturers. This consists in
placing a channel, or trough, directly under the lower sweep of each
connecting rod bearing. Each channel is kept filled to overflowing
by a separate pipe connected with the main lead from the pump, and a
constant level is consequently maintained at all speeds of the motor.
An elaboration of this method consists in attaching one end of each
trough to a rod operated in conjunction with the throttle, so that
as the speed of the motor increases, the end of the channels may be
tilted, with the result that the connecting rod scoop will dip deeper
into the lubricant.

After the proper level in each trough has been reached the excess oil
overflows into the bottom of the crank case. From here, it is again
started on its way by the pump and is distributed to the various
bearings and troughs through the different pipes leading from the pump.
As a further precaution against a smoking exhaust, some designers have
added a baffle plate above each crank case compartment that serves to
reduce the size of the opening through which the oil may be splashed.
With this combination of troughs and baffle plates the possibility of
a smoking motor is practically eliminated.

All motors are not so equipped, however, and in the case of those
provided with the bona-fide splash system, care must be taken to keep
the separate crank case compartments filled to the proper level. Too
high a level in the crank cases will cause the motor to smoke; while
the supply should not be allowed to become so low that when the angle
of the crank case is changed--as in ascending a hill--the lubricant
will run toward the rear and will not be reached by the scoop on the
connecting rod bearing. This latter danger makes it advisable to give
this system plenty of oil when any touring is to be done through a
hilly district.

In some lubricating systems, the oil is supplied as it is used, and
either is discharged with the exhaust, or collects in the bottom of
the crank case, from which it should be drained occasionally. In the
circulating systems, however, which are now used on a majority of the
cars, the same oil is used continuously until it becomes "worn" or
filled with sediment and particles of dirt and other foreign matter.
The pump used for maintaining this circulation may be either of the
plunger, centrifugal, or gear type, and is generally housed in a
portion of the crank case. A strainer is usually placed in the suction
end of this pump for the purpose of removing all the free foreign
matter from the oil before it is again started on its mission of
lubrication. In these systems, the oil well is generally located in a
"secondary" bottom of the crank case. From here it may be drained when
the supply is to be renewed.

Another successful system by which all the bearings of the crank shaft
are positively lubricated is used on many of the best cars. In this
system, a continuous oil hole passes throughout the length of the
crank shaft, including its "arms" and connecting rod bearings. At each
bearing, one or two small oil holes connect with this main artery and
extend radially to the surface. Oil is forced into the longitudinal
oil hole by means of a small pump, and naturally finds its way through
every radial opening to all the bearings. The excess may overflow into
the individual oil wells, from which it will be splashed upon the
exposed portions of the pistons as they descend.

It will be seen that, no matter what modern oiling system is used, the
same kind of lubricant is supplied to all parts of the motor. This
feature makes matters much simpler than was the case when one oil was
used for the cylinders, another, of a different thickness, supplied to
the crank case, and still a third required for the gears. By the old
gravity systems, the flow of oil depended largely upon its viscosity,
or thickness. Therefore, in winter, a thinner oil was required than
in summer, for the more a lubricant is warmed, the thinner does it
become--and vice versa. With the mechanical force systems now in use,
however, practically the same kind of oil may be used throughout the
year--although many motorists believe that better results will be
obtained if a heavier oil is used in summer than in winter. The oil
will be warmed by the motor and it will not require many minutes of
operation before a lubricant made thick by a low temperature will flow
freely and do its work as efficiently as a thinner oil.

But no matter how reliable a lubricating system may be in its
operation, the driver must do his share and make certain that fresh oil
of the proper quality is supplied when needed, and assure himself that
all the passages are free from obstructions. Negligence on the driver's
part may result in one or more "stuck" pistons that will either
seriously injure the motor, or will put it out of commission until the
trouble can be remedied. If a sufficient supply of oil is not fed to
the rubbing surfaces between the piston and the cylinder walls, a high
degree of heat is generated which will tend to expand the piston until
it grips the cylinder so closely that the former cannot be moved. In
this event the motor will stop "dead," and cannot be started again
until the piston has cooled and contracted to its normal size. Even
then, however, the motor should not be run under its own power until
the burned and gummed oil has been removed and the scored surfaces have
been cleaned. While this may best be done by removing the piston--at
which time an examination for any badly burned rings may be made--this
is not always possible, and it may be necessary to run the car home or
to the nearest repair shop before the proper repairs can be made.

In this case, the motor should be turned by hand until it is certain
that the piston is again free in its cylinder. Liberal quantities of
kerosene oil should be poured in through the spark plug opening, and if
possible, the motor should be "rocked" back and forth by the flywheel
to give the kerosene an opportunity to reach all parts of the piston
and rings. The kerosene will serve to cut and remove much of the carbon
and gummed oil and to make the way free for the fresh lubricant,
which should be poured in liberal quantities into the cylinder head.
The flywheel should again be moved back and forth so that the oil will
reach all parts of the piston surface, and after this--if the damage
has not been too great--the motor should be ready for operation.




CHAPTER VIII

COOLING


To enable the parts of a motor to work well, there must be freedom of
motion between all that move in contact with each other. This necessary
freedom of motion is provided for to a certain extent by proper
lubrication, but this is not all-sufficient. The necessity for some
additional friction- and heat-reducing system can be better realized
when it is understood that the temperature of the explosion in the
cylinders of a gasoline engine is well over 2,600 degrees, Fahrenheit.
The melting point of pure iron is less than 2,800 degrees. Therefore
were there no escape for this heat, and could the motor be induced
to run under these severe conditions, the cylinders would soon reach
a temperature dangerously near the melting point. Long before this
point could be reached, however, the intense heat would have expanded
the pistons so that they would become stuck in their cylinders, and
no more explosions could occur. An ominous knock in one or more of
the cylinders, followed by a sudden laboring and final cessation of
operation on the part of the motor, is sometimes the first intimation
that the driver may have that his engine is over-heated; but serious as
a "stuck" piston may seem, it is fortunate that the motor stops of its
own accord, for to continue to run under these conditions of constantly
increasing heat would be to wreak far more serious and permanent damage
upon the moving parts than the broken rings or scored cylinders that
usually result from a lack of lubrication or cooling medium.

A large amount of the heat resulting from each explosion is carried
out through the exhaust pipe in the form of the burned gases, while
other portions radiate into the surrounding air. These outlets are
not sufficient, however, to carry away all the heat that is necessary
to enable the motor to run efficiently, for proper piston lubrication
is exceedingly difficult to obtain at high temperatures. There must,
therefore, be more positive and direct means for carrying off this
undesired heat, and to accomplish this result every internal combustion
motor is provided with a cooling system of either the air or liquid
(usually water) type. Motorcycle power plants and a few of the small
and medium-sized automobile engines employ the air-cooling system; the
great majority of automobile engines, stationary plants, and marine
motors use water as the cooling medium.

Let us consider first the air-cooled system. The area presented
by the outside of a smooth cylinder is not large enough to enable
sufficient radiation to take place. That is, the heat is concentrated
on a comparatively small surface, and this is much more difficult to
keep cool than is the same amount of heat distributed over a greater
area--for the cylinder will be exposed to a larger quantity of fresh
air in the latter case. Therefore many air-cooled engines are provided
with a series of grooves and flanges on the outer surface of the
cylinder. The heat is conducted to all parts of this surface--flanges
as well as grooves--and the area of the surface that is exposed to the
cooling air is greatly increased thereby.

These grooves and flanges may extend circumferentially around the
cylinder, as is the case with many motorcycle engines, or they may
extend longitudinally. Another form of air-cooling system consists of
pins or spines projecting radially from the surface of the cylinder.
The motion of the car through the air is generally sufficient to
create a circulation of the cooling medium, but in order that this
circulation may continue while the car is at rest a high-speed fan
is provided that draws the air from the front toward the rear of the
motor. This serves also to supplement the air circulation produced by
the motion of the car, and keeps the motor much cooler than would be
the case were the machine run without the fan. This fan is generally
attached to a bracket at the front of the motor, and is driven either
by a belt or geared shaft. In some designs, however, the fan blades are
included in the flywheel at the rear of the motor and the air is thus
sucked over the cylinders.

One of the most effective air-cooling systems for use on an automobile
motor consists of the above-mentioned longitudinal flanges and grooves
enclosed in a thin jacket or casing surrounding each cylinder.
These jackets are open at the top and bottom of the cylinders, and
connect with large pipes, or troughs, through which air is forced.
The trough into which the top of the jacket spaces open is connected
with the discharge end of a large fan. The air is thus driven into
the top trough, through each jacket, and into the lower trough, the
farther termination of which is connected with the suction end
of a fan included in the flywheel. The two fans serve to set up a
rapid circulation of air which, by means of the troughs and jackets,
is concentrated upon the surfaces of the grooves and flanges of
each cylinder and none is wasted on parts of the motor that it is
unnecessary to cool. Furthermore, the rear cylinders receive as much
air as do the forward ones, for the trough serves to distribute the
circulation equally along the grooves and flanges of each.

Inasmuch as the heat from an air-cooled motor is radiated directly
into the current of air itself, the surface is very susceptible to
temperature changes from the interior. Thus, if the car is run for
a great distance on the low gear, and the cylinders become hot in
consequence, a larger amount of heat will immediately be radiated from
the cooling surfaces than is the case when the motor is running slowly.
A "coast" down a short hill, however, will serve to cool the motor
rapidly, for if the engine is run from the momentum of the car with
the spark turned off, cool air will be drawn into the cylinders, and
this, in addition to the circulation of cold air on the outside, will
reduce the temperature of the engine rapidly. This is a feature of the
operation of an air-cooled motor that is not possessed to so large an
extent by those of the water-cooled type.

It is, perhaps, hardly accurate to apply the term "water-cooled" to
the ordinary type of automobile motor. Water is merely the medium
that transfers the heat from the cylinders to the cooling surface of
the radiator. As air is used to cool this heated water, we see that
the only difference between the two systems lies in the point of
application of the actual heat-absorbing medium--which is air in both
cases. Thus in the air-cooled motor the air is carried directly to the
surfaces to be cooled; while in the other type, the heat is transferred
by means of the water to the point where it may be effectually
discharged into the air.

Each cylinder of a water-cooled motor is surrounded by a space known
as the water jacket. This space is generally cast with the cylinder,
although in some designs of motors the jackets are formed by the
subsequent application of a copper casing that serves to retain the
water. The water jackets are connected with each other by means of
piping and water-tight joints so that the water will pass successively
from one to the other. If the water remained in these spaces, it would
soon be warmed to a temperature far above the boiling point, steam
would be formed, a high pressure generated, and infinite harm would
result--both to motor and to passengers. The piping, however, does not
end with the connections between the cylinders, but extends to and from
the radiator.

This radiator is a large, perforated structure placed either forward of
the motor to form the end of the bonnet-covering, or in front of the
dash between it and the rear cylinder of the engine. The radiator is a
mass of small cellular or tubular passages, each one of which possesses
an exceedingly large outer surface in proportion to the amount of water
that it can contain. When the hot water reaches the radiator it is
distributed to these many cells or tubes, and is thus spread over a
large cooling surface. A large fan is usually located directly behind
the radiator, and as this serves to draw the air rapidly through the
openings between the cells or tubes, cooling is greatly facilitated.

There are several types of radiators in general use. Some consist of
a number of flat cells placed in such a manner that regular-shaped
air openings will be formed. Each side of each flat water cell abuts
on an air passage. Such a radiator is known as the honeycomb, or
cellular, the former term being applied to those whose cells resemble
a honeycomb. The tubular radiator consists of a number of vertical,
parallel tubes through which the water passes, and which are placed
a sufficient distance apart to provide ample air passages between
them. Each tube is covered at frequent intervals with fluted, circular
flanges that serve to increase the radiating surface in much the same
manner as do the grooves and flanges on the cylinders of the air-cooled
motor. All air passages in any radiator extend directly through the
width of the radiator, while the water circulates from top to bottom in
a vertical direction.

The reason for this circulation of the water will be apparent if we
call to mind a bit of our elementary physics. When water is heated, it
expands and rises, and for this reason, we always find the surface of
the water in a teakettle warmer than is that at the bottom--although
the latter is closer to the fire. As the water is circulated through
the radiator, it is cooled by the passage of the large amount of air
through the openings between the cells or tubes. The water thus cooled
sinks to the bottom of the radiator and is replaced by the water
just heated by the motor. The cooled water is conducted to the bottom
portion of the end cylinder, and passes to the others in succession,
gradually rising as it is heated, until it is again forced to the
radiator at the top.

There are two methods of circulating the water through the cylinder
jackets and radiator. The most common method consists of the
introduction of a pump in the lower portion of the circulating
system. In the case of automobile motors, this pump is driven by
gears connected with the crank shaft of the engine. Such a pump will
be either of the gear or centrifugal type, and will suck the cooled
water from the lower portion of the radiator, and force it through the
jackets. The second method is known as the thermo-syphon system because
the circulation is automatic and depends upon the cooling of the water
in the radiator. When the cooled water sinks, a syphon action is formed
that tends to draw the hot water from the cylinder jackets, and the
automatic circulation will thus continue as long as the successive
heating and cooling take place.

Inasmuch as the pump is driven by the crank shaft of the engine, its
speed will be proportional to that of the motor. The same holds true
of the fan that serves to draw the air through the radiator. It will
thus be seen that both the water and the air are forced at a more rapid
rate when the motor runs at high speed, and that therefore the extra
heat generated by the more frequent explosions in the cylinders will be
counteracted to a certain extent. The increased number of explosions
and the higher speed at which the fan turns also cause quicker heating
and cooling of the water by the thermo-syphon system, thus forming a
more rapid circulation. Inasmuch as the force exerted upon the water by
its cooling and heating is not as great as that formed by a high-speed
and efficient pump, the pipes and connections of the thermo-syphon
system must be of ample size in order to keep the resistance to the
passage of the water as low as possible. Care must also be taken in the
design of this system so to construct and connect the pipes and jackets
that the hot water will be allowed to rise and the cool to descend,
and thus to make possible the syphon conditions on which principle the
circulation is based.

The ability of the radiator to carry off the heat from the water
depends upon the rapidity with which the air passes through the
passages provided for the purpose. The amount of air passing through
is determined by the speed of the suction fan and the rapidity of
travel of the car itself against the wind. It has been shown that, when
the motor runs at a high number of revolutions, the fan turns faster
and the rapidity of circulation is increased. But if the car itself
does not increase its speed in proportion to the higher revolutions of
the motor, the maximum amount of air will not be forced through the
radiator passages, and the excess heat will not be carried off entirely
from the cylinders. This is a condition that prevails when the motor
is run on low gear. The speed of the motor is increased, while that of
the car is reduced; additional heat is generated in the cylinders, but
the speed of the air is not increased in proportion. Therefore a motor
that is driven a long distance on the low gear will have a tendency to
overheat.

Water under atmospheric pressure cannot be brought to a temperature
above 212 degrees Fahrenheit without being converted into steam.
Therefore, when the heat from a water-cooled motor cannot be carried
away sufficiently fast, the water in the circulating system will begin
to boil. As long as water remains in the jackets, the temperature of
these spaces cannot well rise above 212 degrees, and consequently there
is small danger that a water-cooled motor will become overheated to
the point at which the pistons will "seize" in the cylinders. The
moment the water in the circulating system begins to boil, however,
exceedingly rapid evaporation naturally takes place, and the water will
soon entirely disappear in the form of steam and vapor. To run the
motor under these conditions will mean that pistons and rings will soon
become stuck in their cylinders, although liberal quantities of oil
will sometimes delay this inevitable result.

But even when the cooling water is not brought to the boiling point
there is a vapor that is constantly dispelled from it whenever its
temperature is brought above that of the air. The water system of
an automobile must therefore be replenished at irregular intervals,
depending upon the amount and nature of the running to which the car
has been subjected. The older cars were provided with an extra water
tank, generally located under the seat, and connected directly with
the water jackets and the radiator. The usual water-cooling system of
the present-day car, however, is self-contained--that is, there is no
separate tank for the storage of the water. The water is poured into
the top of the radiator, and from this high point it reaches every part
of the circulating system. Whenever the radiator will accommodate a
couple of quarts, or more, it is well to fill it, for _too much_ water
_cannot be used_ on the modern design of cooling system. It is true
that a motor runs at its highest efficiency when its temperature is
as great as that at which proper lubrication of the pistons can be
obtained--for a gasoline engine is a "heat engine," and the greater
its unnecessary heat losses, the less will be the power developed by
it. But a motor cannot be kept at the proper temperature by reducing
the amount of cooling water in its circulating system. The best method
is to lessen the rapidity with which the water is cooled, and this
may be accomplished by placing a leather flap, a cardboard, or other
obstruction over a portion of the radiator to reduce the number of
openings through which the air may pass. It should only be necessary
to do this in the coldest weather, however, for the cooling system
of every motor is designed to maintain the proper temperature on all
except the hottest or coldest days.

It has been stated in a preceding paragraph that continued running on
the low gear is the most frequent cause of overheating a motor. This
is true, but it is not the only cause. Obstructions in the circulating
system that reduce the flow of water will have this effect, as will
also deposits on the interior of the cylinders that serve to prevent
the proper transfer of heat to the water in the jacket spaces. Removal
of the carbon will remedy the latter trouble, but to clear out the
circulating system is more or less of a complicated matter. Stoppage in
the pipes or radiator cells may be caused by a lime deposit from "hard"
water that may have been used in the circulating system. There are
preparations intended to remove this deposit, but such should not be
used without first advising with the maker of the car or an experienced
repair man. A series of battered cells in the radiator may reduce the
number of cooling spaces that should be traversed by the water, and
thus the hot water cannot be distributed over as great an air area as
is necessary to maintain the motor at the proper temperature. Such a
condition will be apparent from a marked difference in temperature
between the affected portion of the radiator and the remainder. If a
deposit has been formed on a certain series of cells, or if they have
been obstructed in any other manner, the hot water cannot circulate
through this section of the radiator, and it will remain comparatively
cool.

Water is a liquid that remains in its fluid stage only through a
temperature range of 180 degrees--at atmospheric pressure. At 212
degrees it boils and turns to vapor, while at 32 degrees it freezes and
becomes a solid. In neither of these stages does it form a desirable
cooling medium for a gasoline motor. Of the two, however, its solid
stage is the more harmful to the motor. Not only will it cease to
flow when it becomes ice, but the expansion of the water during the
formation of the solid is liable to burst its retainer--whether it be
the cells of the radiator, the pump, pipes, or even the cylinder walls
themselves. It is the radiator that is the most liable to suffer from
such a cause, however, for each cell contains so small an amount of
water that the liquid will be brought to the freezing point before the
larger volume in the jacket spaces approaches this temperature. Of
course the water will be kept well above the freezing point when the
motor is running, and it is only when the machine has stood idle for
several hours that care must be taken to prevent the formation of ice
in the circulating system.

Aside from keeping the car in a warm place whenever the motor is to be
at rest more than two hours, there is only one method of preventing
the cooling water from freezing, and that is by the introduction of
some chemical that lowers the point at which the liquid will turn to a
solid. There are several ingenious heaters available that are attached
to the circulating pipes and that serve to keep all of the jacket water
warm; the use of these producing the same conditions as though the car
were kept in an artificially-heated garage.

One of the most common liquids used in the cooling water to prevent
freezing is alcohol. If equal parts of wood alcohol and water are used
in the cooling system, the resulting mixture will not freeze until
it reaches a temperature colder than 25 degrees below zero. A weaker
mixture--one having 25 per cent. of wood alcohol--will freeze at
about zero, and it therefore depends upon the prevailing cold-weather
temperature as to the proper proportion that should be used. It must
be remembered that the boiling point of alcohol is much lower than is
that of water, and that therefore a mixture that will not freeze in
exceedingly cold weather is liable to boil away on the first moderate
day on which the car is run. The above-mentioned 50 per cent. mixture
of wood alcohol and water will boil at 135 degrees, while the 25 per
cent. solution will withstand a temperature 40 degrees higher before it
is transformed into vapor. As the lower temperature will be reached
easily if the motor is run for some time in comparatively moderate
weather, it will be seen that the stronger mixture should be used only
where winters are very severe. It must also be borne in mind that,
as alcohol boils more readily than does water, it follows that it
will evaporate more easily, as well. Therefore, in order to maintain
a uniform proportion of wood alcohol to water, the former should be
replenished more often than is the latter.

Glycerine is another substance that is often mixed with the cooling
water to prevent the latter from freezing. A 50 per cent. mixture of
this and water has a freezing point of about zero, or slightly lower,
and boils at practically the same temperature as water--210 degrees.
Combinations of wood alcohol and glycerine may be used--equal parts of
each being the usual proportion--and thus various freezing and boiling
points may be obtained.

The radiator is one of the most delicate parts of the motor car's
construction, and yet it is the most exposed to flying sticks and
stones that may be thrown up by the rapid travel of the car. The
car owner may do well to follow the practice of many racing drivers
who place a heavy wire mesh screen in front of the radiator as a
protection against obstacles that may be struck by the front of the
car. It would seem that sticks and stones would be thrown toward the
rear of the car, and would therefore avoid the radiator by a wide
margin, but experience has proved that, at high speed, such loose
pieces are frequently forced forward and are _run_ into by the front of
the car.




CHAPTER IX

TWO-CYCLE MOTORS


There has always been a strong prejudice in favor of the four-cycle
motor for the power plant of the gasoline automobile. This may be due
to the fact that designers have spent most of their time and energy on
the development of this engine, and that therefore the two-cycle type
has not yet been sufficiently "tried out" in the motor car to enable us
to judge fairly as to its real merits. Certain it is that in the few
instances in which the two-cycle motor has been used as an automobile
power plant, the results have been highly satisfactory, and the present
vogue of the four-cycle motor--with well over 98 per cent. of the
automobiles now made adhering to this type--is largely due to popular
prejudice in its favor.

As has been described in the first chapter of the present volume,
the four-cycle motor devotes a separate stroke to each of the events
of expansion, scavenging or expulsion of the burned gases, suction,
and compression. The two-cycle motor, on the other hand, devotes but
two strokes to these four events, and there is therefore an explosion
twice as often in the two-cycle engine cylinder as is the case with the
four-cycle type. But in lieu of the suction stroke of the four-cycle
motor, there must be some method of forcing the charge into the
cylinder of the two-cycle engine. The base, or compartment below the
piston, in which the crank revolves, is used for this purpose. As the
piston travels upward on its compression stroke, a partial vacuum is
formed in the base, and if a passage is opened between this compartment
and the carburetor, the charge will be sucked in.

All outside connections with the base are tightly closed on the
down-stroke of the piston, and consequently the recently-inhaled charge
will be compressed, ready for its entrance into the cylinder above the
piston as soon as the connecting passage is opened. This passage is
opened, as has already been described, at the bottom of the stroke and
the compressed charge rushes in and fills the space in the cylinder
that at that time is being vacated by the exhaust gases.

The majority of two-cycle motors are made without any valve mechanism,
the opening and closing of the passages being entirely automatic.
These passages are cast with the engine and lead into the cylinder
through openings in the walls called "ports." The opening leading from
the cylinder to the exhaust pipe, or exhaust port, is placed near
the bottom of the stroke so that it is covered by the piston, except
at the lower extremity of the travel of the latter. Just below the
exhaust port, and on the opposite side of the interior of the cylinder,
is placed the intake port, or opening of the passage connecting the
cylinder with the base.

Now, as the piston is forced downward, it uncovers the exhaust port and
an easy means of escape is furnished for the burned gases. Immediately
after this, the intake port on the opposite side is uncovered by the
still-descending piston, and the previously compressed charge, which
is only awaiting the opportunity in the base, "blows" in. The exhaust
gases are still escaping when this happens, and therefore it is
necessary to prevent the incoming charge from passing directly across
the top of the piston and out through the exhaust port before use has
been made of its explosive qualities.

Consequently, to keep it in its proper path, a baffle plate is attached
to the top of the piston which serves to deflect the incoming charge
toward the top of the cylinder, and this not only prevents the loss of
the mixture, but also furnishes a blast of air that helps to blow out
the burned gases. On the return of the piston to the top of its stroke,
it first passes over the intake port and then covers the exhaust port,
effectually closing both and preventing the escape of the charge during
compression. While this is going on, it must be remembered, the piston
is forming the partial vacuum in the base, which serves to draw in the
charge for the succeeding explosion.

If the charge is drawn directly into the base from the carburetor, a
check valve must be used in the pipe connecting the two; otherwise
the mixture would be forced back into the carburetor the instant the
piston began its descent. A two-cycle motor drawing its charge in this
manner is known as the two-port type, for there are only the exhaust
and the inlet ports in the interior of the cylinder walls. The passage
connecting the carburetor with the base may enter at the bottom of the
cylinder, for this space and the base are the same when the piston is
at the top of its stroke. Thus if this port is placed so that it is
uncovered when the piston is at the top of its stroke, it will admit
the charge to the base at a time when a partial vacuum has been created
in this compartment by the upward movement of the piston.

This port is again covered as soon as the piston starts on its
downward journey, and thus the charge is prevented from escaping until
the intake port connecting the base with the top of the cylinder is
opened. Such a two-cycle motor is known as the three-port type, and
it will be seen that not even an automatic check valve is used in its
passages--and it is consequently a "valveless" motor in the liberal
interpretation of the term.

The high velocity of the charge recompenses for the short time that the
port is uncovered, and consequently the base is filled with nearly as
large an amount of charge as is the case with the two-port motor--which
allows the incoming gases to enter the crank case during the entire
upward stroke of the piston.

It will thus be seen that the piston of the two-cycle motor acts as
a pump in two ways. First, the vacuum is formed that serves to draw
the charge into the crank case, or base, of the motor; and second,
the return stroke of the piston compresses this recently-inhaled
charge and makes it ready to be "shot" up into the cylinder as soon
as the piston has uncovered the port that forms the upper terminal of
the communicating passage. There can, of course, no greater amount of
fresh charge enter the cylinder than is drawn into the crank case.
Consequently, the amount to which the cylinder will be filled depends
upon the vacuum formed and the pressure exerted upon the charge by
the succeeding down-stroke of the piston. It is to be supposed that
the piston rings will be tight and that none of the charge can escape
by them, and therefore the vacuum formed and pressure exerted in the
crank case will depend entirely upon the displacement of the piston
in its travel compared with the total capacity of the crank case. In
other words, if the crank case is large and the piston is small and
travels but a short distance, its pump action on the entire volume will
be small. But if the crank case is small and the travel of the piston
alternately doubles and halves the volume, the motion of the piston
will cause the pressure in the crank case to vary greatly.

In a preceding paragraph it has been described in what manner the
incoming charge in the two-cycle motor was used to "scavenge" the
cylinder, or rid it of burned gases, by deflecting the mixture and
allowing this to force out the remaining exhaust before the exhaust
port was closed by the upward motion of the piston. It is evident
that the greater the force, within certain limits, with which the
charge enters the cylinder, the more perfect will be the scavenging
action. But there is a limit to the pressure that can be attained by
the mixture when it is compressed in the crank case previous to its
discharge into the cylinder. This limit is determined by the size
of the space required for the revolution of the crank and "big end"
of the connecting rod, and by the volume displaced by the motion of
the piston. The crank must have room in which to revolve, and the
displacement of the piston can only be the area of its top multiplied
by its length of stroke. Thus eight pounds per square inch is about
the usual limit of crank case compression with this type of two-cycle
motor. This may be varied slightly one way or the other by the
arrangement of the ports, but it makes slight difference whether the
motor is of the two- or three-port type so far as this consideration is
concerned.

Two-cycle motors have been designed which combine the principles of
action of both the two- and three-port types. The most important
departure from the generally-accepted type of two-cycle motor, however,
is the design in which the charge is fed into the cylinder from a
chamber that is absolutely independent of the crank case proper. This
may be accomplished in several ways. There may be what is termed a
"differential piston" in which a separate plunger operates in the
interior of the hollow "trunk" piston, and by means of the proper
connection with the crank shaft compresses the charge in the chamber
thus formed at the time it is to be forced into the cylinder.

Another design for obtaining intake compression independent of the
crank case consists of a collar, or circular enlargement at the base of
the piston. This collar reciprocates within the lower portion of the
piston in a chamber which has been bored to the exact size. The collar
consequently forms a variable base for this compartment, and as the
piston descends, the collar travels with it, thus drawing in a charge
of the fresh mixture. On the upward stroke, this mixture is compressed
by the collar as it reduces the size of the compartment. It will be
seen that such a motor can be designed to compress the charge to almost
any amount.

Inasmuch as the mixture, as mentioned above, is compressed on the
up-stroke of the piston, it is evident that it cannot be discharged
into that particular cylinder at that time--for the mixture should be
delivered to its cylinder only when the piston is at the bottom of
its stroke. In the case of a four-cylinder engine, however, one of
the pistons would be in the proper position for the entrance of the
charge, and it is into this cylinder, that the compressed mixture is
forced. The compression space in each cylinder, therefore, works for
its neighbor, rather than for itself.

This interchange of courtesies is obtained through the good offices of
a distributor in the form of a rotating, hollow cylinder having ports
cut throughout its length that register with corresponding passages
leading to the various cylinders. This distributor is timed with the
crank shaft of the motor, and may be driven either by a gear or by a
silent chain. As the mixture is compressed in the separate chamber of
one cylinder, the passage leading to the distributor is opened by the
revolution of the latter, and the charge is led through this passage,
the distributor, and thence through another passage--also opened by the
distributor--to the proper cylinder. The cylinders thus operate in
pairs, one receiving its charge while the other is about to begin its
explosion stroke--and vice versa.

The force of the explosion in a gasoline engine cylinder is not only
dependent upon the amount and nature of the inflammable mixture
admitted, but upon the force with which it is compressed, as well.
The average compression pressure of a two- or four-cycle engine of
the ordinary type, is from 60 to 70 pounds per square inch. Inasmuch
as this pressure, assuming that the rings and valves are tight, is
proportional to the displacement of the piston stroke compared with the
volume of the clearance space, the amount of compression is constant at
all speeds and loads of the motor. Should it be possible to increase
this compression at will, it would be found that, with a warm motor, a
pressure in the neighborhood of 100 pounds per square inch would serve
to generate sufficient heat to ignite the mixture before the formation
of the spark--for it is one of the elementary laws of physics that a
gas will become heated when compressed. It is for this reason that the
compression pressure of the ordinary automobile motor is kept in the
neighborhood of 70 pounds per square inch.

A method of varying compression pressure to meet individual load
requirements has been devised for some motors, however, and while such
types are not as yet in general use in automobiles, it is probable that
the near future will find much advancement along these lines. One such
two-cycle motor that has been designed especially for automobile use
employs a separate air compressor driven by the engine itself and used
as the clutch and variable speed transmission of the car. The amount of
pressure generated in the compressor is dependent upon the resistance
offered to its operation--or, in other words, it increases with
additional load carried by the motor. The compression, or compressed
air, rather, is carried directly from the compressor to the cylinders
of the motor, being admitted at the proper time by a rotary valve
driven by the crank shaft. Thus the compression in each cylinder is
automatically regulated by the load, and a motor of this type possesses
a high "overload" capacity.

The motor mentioned above operates on somewhat the same principles as
those found in the Diesel engine, which will be, as many predict, the
ultimate type of internal combustion motor. The Diesel motor is not
necessarily a particular make of engine, but bears the name of the
originator of the principles involved. These are distinct from those
of the Otto cycle, which is the principle upon which practically all
automobile motors operate. The Otto cycle consists of the well-known
series of events in the cylinder, as follows: Ignition, followed by the
explosion, or expansion of the burned charge; discharge of the exhaust
gases, or scavenging; admission of the fresh charge, suction; and
compression of the newly-received mixture previous to ignition and the
repetition of the cycle. In speaking of the Otto and Diesel engines, it
must be borne in mind that they are referred to as a class, rather than
as a particular make--as one would mention poppet valve or sleeve valve
engines--for there may be many manufacturers of each type.

Although the Diesel principle may be applied to either the two or
four-cycle type of motor, it is to the former design that it lends
itself unusually well. This motor operates a two-stage air compressor
in conjunction with a storage tank. At the beginning of the compression
stroke, pure air under high pressure is admitted to the cylinder.
In its upward travel, the piston compresses this air to a pressure
approximating 500 pounds per square inch. While it has been shown that
such a pressure is about five times more than enough to generate
sufficient heat to cause premature ignition, it must be remembered
that, unlike the ordinary type of motor, this is only pure air that is
injected into the cylinder and contains none of the explosive gasoline
vapor. At the top of the stroke, however, when the compression is at
its maximum, the fuel is injected directly into the cylinder without
having been previously vaporized.

This is another feature in which the Diesel motor is entirely different
from the Otto type, for the latter must employ a carburetor to vaporize
the fuel before it can be admitted to the cylinder. But inasmuch as
there is already a pressure approximating 500 pounds per square inch
in the cylinder of the Diesel motor at the time the fuel is injected,
there must be a force behind the latter of 750 or 1,000 pounds per
square inch in order to enable it to overcome the resistance of the
highly-compressed air in the cylinder. In short, the liquid fuel is
sprayed directly into the cylinder at a pressure of 750 or 1,000 pounds
per square inch. This tremendous pressure is sufficient, not only to
vaporize the particles of fuel as soon as they enter the cylinder
from the nozzle, or "atomizer," but to cause them to burst into
flame, as well. In other words, the compression of the air previously
has generated sufficient heat in the cylinder to ignite the fuel
immediately on its admission.

The fuel continues to be injected into the cylinder during the greater
part of the down-stroke of the piston. In this respect, also, is the
Diesel motor radically different from the Otto type, for the latter
receives its full charge at one time and fires the entire amount in
a single "explosion." In the Diesel motor, on the other hand, the
ignition continues as long as fuel is admitted, and thus this engine
is of the internal _combustion_ type in the strictest sense of the
word. It is, after all, the expansion of the gases due to the heat of
combustion that produces the power in a gasoline engine, and if the
fuel can be so admitted that it can burn during the greater part of the
stroke, a high efficiency will be obtained.

The exhaust gases of the ordinary two-cycle motor pass out of the
exhaust port as it is uncovered by the descent of the piston. Those
that remain are forced out by the sudden admission of the fresh charge,
which is deflected upward and is intended to scavenge the top of the
cylinder. But it is claimed that thus employing the fresh mixture as
a scavenging agent is wasteful of the fuel-permeated charge and does
not conduce to efficient running. The system is simple in the extreme,
however, and does its work well in small installations in which fuel
economy is not of vital importance. But in the two-cycle Diesel type
of engine, the high pressure of the pure air is used for scavenging,
and as this is admitted with so large an initial force, the exhaust
port may remain uncovered for a longer period than would be the case
were the air to rely entirely on the up-stroke of the piston for its
compression. Then too, whatever air may escape contains no fuel, and
consequently efficient scavenging may be obtained without waste.

At the high pressure at which the fuel is injected into the cylinder
of the Diesel engine, practically any grade of gasoline, naphtha,
kerosene, crude oil, or other form of petroleum can be vaporized.
The compressed air employed in the compression and injection of the
fuel is also used for starting the motor, for this is not a type that
is amenable to hand cranking. Thus the Diesel type of engine can be
run in any weather on any grade of oil fuel, and as the carburetor
and electrical ignition system are absolutely eliminated, two of the
great sources of trouble of the automobile motor are absent--and this
feature, alone, even more than the superior economy of operation, will
appeal to the average motorist.

Just when this type of motor will be taken up by automobile designers
is difficult to state. The Diesel type of engine has proved so
wonderfully successful for large stationary power plants and for marine
purposes, and its reliability is so absolute on all grades of fuel,
that this motor may solve the failing-gasoline-supply problem. As yet,
about 100 horsepower is the smallest unit that has been made in any
quantities, but it was recently announced that this type would, in
the very near future, be built for motor trucks and other commercial
vehicles. Consequently, it is well for all those interested in the
application of the two-cycle motor to the automobile to understand the
elementary principles on which this radically-different type operates.




      *      *      *      *      *      *




Transcriber's note:

Inconsistent hyphenation has been retained unless one form predominated.

The following corrections have been made:

p. 19 This give a much -> give changed to gives

p. 34 purpose of cleanning -> cleanning changed to cleaning

Everything else has been retained as printed.



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