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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