Evening star., 1925-11-01
BY FREDERICK c. RUSSELL.


Automobiles. like human beings
frequently develop the most serious
ailments without the slightest fuss
about il. All at once one discovers
that something has gone all wrong,
and there is nothing 10 do but call in
the specialists. 1t is a costly propo-
sition and quite unnecessary because
IT can be prevented
Just q little test now and again can
be utilized to detect any possibilities
Of trouble ahead. and. of course. when
one has unearthed possibilities pre-
vention is a far simpler process than
remedy. But that is s'eaking rela-
lively. The motoriSt mus not assume
that prevention in itself Is necessarily
a matter so simple as rolling off Il
log
This is eXcellently Illustrated in the
case of the lung test" for autOmo-
bile engines. The power plant under
The hood breathes a mixture of air and
gas vapor. utiliZes il for power and
then eXpeis it. The process appears to
be simple enough yet it is remarka-
hly complicated. Naturally the process
of preventing any divergence from the
normal breathing order cannot be a
mere matter of observation and ac-
tion such as inspecting the oil level
of the CrankcaSe and ordering a quart
OF good oil If II 5 low.
Motors breathing"
One first must have clearly in mind
the course of the gas vapor and air
mixture as II finds its way TO and from
the lungs of the engine. Briefly, il is
led by suction up through the intake
manifold and thence into each cylinder
by turn. Once in a cylinder it is sup
posed TO be trapped there by the sud
oil . l.
ii was drawn and then compressed.
iGnited and allowed to expand. An
exhaust valve then opens. permitting
the burned gas to escape through the
exhaust manifold muffler. another
short stretch OF pipe and then out into
the air.
What it actually does do. however.
may vary according to the condition
o. the engine-and. in particular. the
determination of the car owner to
have his servants give him maximum
service. This vapor seems TO be de
termined to skim over certain por-
lions of its course without doing its
share: and it is here the motorist has
TO be alert. for every time the breath
ing process is not up to standard the
engine will lack power and waste fuel
Just as in the case of the human
being, however, there are various
ways of testing for lung capacity"
In the case of the automobile engine
II Is matter of Cranking the power
plant by hand with the ignition off
This tests for compression which is
an index Of the inability of the trapped
gas vapor to escape from its cylinders
when the pistonS are in process of
compresSing it. Stated in other terms
one can also say that the compression
test Is an index of the ability of the
engine to keep the gas vapor strictly
on the job.
1t Is omportant TO note here how
ever, that compression ratios differ
with different types Of engines, just
as there are persons of the deep
breath" and short breath" type so
are there engines with high compress
sion and others with low. The motor
1st has no cause for alarm until he
detects a variation. When compress
sion is high in some cylinders and low
in others he should begin seeking q
cause. 1t is just as though a deep
breather" should suddenly develop
tendency to be short of breath.
Cylinders Vary Greatly.
1t is also important to remember
when testing for compression that
few engines will show equal compress
sion for every cylinder. A slight vari-
alton is usually noticeable. But most
car owners will notice that their en-
g1nes show rather wide variation. a
fact that ties up with the suspicion
that most engines could profit through
a bit of tuning up. Lacking scientific
equipment, the motorist is forced TO
test by the feel" of the crank han
die as he comes up on the compres-
sion stroke of the respective cyln-
der being tested, but if he goes over
the engine several times the chances
are that he will not be far wrong in
determining whether the engine needs
attention.
BY opening all the pet cocks except
the one for the particular cylinder
being tested it is possible to feel
through the crank just about how we'll
the cylinder is holding the compressed
gas and how long. Whatever cylinders
reveal high compression las compared
with the average for the enginel may
be considered in good order so far as
lung capacity" goes, but when one or
two show low compression it is high
time to determine what's wrong-and