Evening star., 1925-08-23
No. 112-Two and Four Cycle.

Smiths interest IN the tnree-point
suspension idea in engine design en-
couraged him to keep his ears open
for other interesting topics more or
less strange to the average motorist.
Being in a receptive frame of mind.
therefore, he was quick to sit up and
take notice when he overheard two
car owners discussing the possibility
of the return of the two-cycle type
Of engine, provided certain obstacles
could be overcome.
Smith lost no time in seeing MS Ia
vorite repairman.
Joe" he said, 81 overheard some
talk about a two-cycle automobile en-
gine today, and it's got me puzzled.
But before ! ask you TO enliShten me
I'd like to know what sort of engine
I've got in my own car. l know II 8
a valve-in-the-h head six and all that.
But there's evidently some feature
about ii I've overlooked.
Joe stopped work to light ciga-
rette and invite Smith to make HIM
self at home, running boards serving
as morris chairs. For moment Joe
appeared nonplussed how to explain
so simple difference between the two
basic types Of gasoline engines.
Yours is four-cycle engine, ne
began Most internal combustion en-
gines today are of this type but the
only way l can explain why It's the
popular type is by telling you how a
two-cycle engine works.
Explaining the Engine.
Let 'er CO." Smith agreed. "1'l
interrupt you when you get too tech
n5cal."
I'm not going to be technical" Joe
said. ''If you drive a car you know
or YOU ought to krow-the general
idea Of a cylinder and what happens
in it. In cylinder you have hollow
piston which travels up and down. re-
volving a shaft beneath 1t by being
Joined to dts crank with a connecting
rod. Explosion of compressed gas va
por by an electric spark drives the
piston down; momentum Of the fly
wheel carries it up again. That's the
idea of it in a nutshell.
THE next thing is to provide some
means of admitting gas Vapor 10 the
cylinder and releasing the burned gas
For this we use valves. The two
cycle engine being an early develop
ment, the first valves that occurred to
engineers were holes or ports in the
cylinder wall which would be uncov.
cred when the piston was down. One,
of these ports connected with the car
buretor, the other with the exhaust.
But there was also a tube from the
intake port to the air-tlght base or
the motor.
1.-The next point is TO see the thing
in operation. We crank the engine
and make the piston rise to the top OF
its cylinder. The suction created In
the engine base draws gas vapor into
the base from the carburetor. The
piston, having compressed some gas
at the top, travels down on its power
stroke when the gas Is fired. In go
ing down it forces out the gas In the
base. This comes around through the
intake port to the top of the cylinder,
now that the piston is down. At the
same time the burned gas goes out
the exhaust port, the two gases be-
ing somewhat separated by battle
plate attached to the piston. Thus
every other stroke of the piston Is
power stroke. So we call this type
two-cycle.'
FOur-Cycle Operation.
I'm the four-cycle engine the base
of the cylinder plays no part In the
Job. Ports are replaced by mechant.
cally operated valves, one furnishing
an opening for the exhaust. the other
for the intake. These are operated
by the camshaft. opening and closing
at the exact time. When the piston
comes up the exhaust valve opens and
the cylinder is completely cleaned out.
When the piston travels down the ex-
haust valve closes, the intake opens
and the piston sucks IN fresh gas va
por. When it comes up the second
time both valves stay closed, the gas
is compressed, fired and the piston
goes down on its power stroke. There
are four distinct strokes or cycles"
well, that seems more sensible In
every way Smith commented. The
piston does work only on every fourth
stroke, but the arrangement is so
much more accurate that the engine
should be much more efficient than a
two-cycle. should think the gases
would be mixed in the two-cycle en-
gine. SO that the cylinder would never
be clean. With the sort of gas we
use today the engine would be skip
ping half the time"
"Now you know why there isn't
much chance for a return of the two
cycle engine in automobiles" Joe con-
cluded, returning to his work. ITO
be efficient 1t would have to be COM
pletely revised. But what really
killed it was the advent of the multi
cylinder engine. They found that one
cylinder engines offered too much
vibration, so more cylinders were
added. And with more cylinders the
advantages of having each cylinder
deliver an impulse for each revolution
of the crankshaft were unnecessary.
Listen to the exhaust Of an 8-cylinder