CHAPTER I_The Gasoline Motor

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THE GASOLINE MOTOR

HAROLD WHITING SLAUSON, M. E.

Author of "The Motor Boat"

Outing Handbooks

New York

Outing Publishing Company

MCMXIII

Outing Publishing Company

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

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.