Evening star., 1921-10-02

which, or on its upward stroke, the
cylinder wall receives it's supply or
film of lubricating oil. being carried
up on this stroke by the piston and
it's rings.
"After passing top center and on it's
return or downward stroke the ere
alton of a partial vacuum within the
cylinder draws in the mixture of fuel
This fuel mixture Immediately comes
into contact with the film lubricant
on the cylinder wall brought up on
the previous exhaust stroke. The
period Of time of this contact be-
tween the fuel mixture and cylinder
wall lubricant is naturally dependent
upon the length of stroke of the mo-
| tor and the revolutions per minute of
the motor. There is. therefore. an
immediate and direct effect establish
ed-viz.. that of the fuel mixture
combining with the film of lubricant
on the cylinder wall. reducing the
viscosity of the body of the film as it
becomes diluted. the diluted film hav-
ing an immediate tendency to drain
back into the crankcase.
1.-The position of the oil pump being
in the base Of the motor and drawing
its oil from this point. repeats the
operation. with the subsequent result
that the aforementioned diluted film
of oil is constantly draining into the
crankcase: and having a lesser spe-
cific gravity. remains on top of the
good oil in the lower portion Of the
crankcase. 1t can be readily under
stood that within a short time the
entire volume of oil in the case is
reduced to specific gravity of that
OF the draining or diluted film re-
ferred to; having little. if any. lubri-
eating value.
Other Important Factors.
II these circumstances were all we
We're confronted with. our problem
might be less serious. However, we
have not as yeffaken into consider
alton the return or compression stroke,
curing which the greatest dilution of
the lubricant takes place. The fuel
mixture during compression stroke is
compressed to as high as forty five
pounds per square inch, the greatest
dilution taking place during this
stroke, as can readily be understood
Conversely the film of oil on the evil
inder wall should be the strongest
during this stroke in order to feel the
clearance between piston and rings
and the cylinder wall Leakages will
naturally occur to some degree and
the amount of leakage will depend
upon the mechanical fit of the piston
ring in it's cylinder. as well as it's fit
The mixture that escapes has. all of
the component parts of the fuel mix
ture in the cylinder at the time of the
leakage. whether on intake or ex-
haust stroke. and the fuel content is
absorbed by the lubricating oil
Again, having passed through the
creative factor of the cycle. let us
pass on to the resultant-the power
stroke. The film of oil on the upper
part of cylinder wall during the first
part of the power stroke or, more
clearly. at the point of combustion. is
partially destroyed, the volatile prod
ucts combining with the fuel. The
lower part of the film resists the re-
duced heat of the gases of combustion
to an increasing extent as the gases
expand. 1t is at this point that car
bon is formed. due to this great de-
composition of the lubricant. The car
bon deposits are heaviest where the
destruction of the film Is the greatest
At the completion of this power stroke
the oil film on the cylinder walls is
in the poorest condition. it's remedy
being that of the return or exhaust