The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1924-09-10

carbon have accumulated around
the seat of an intake valve that
valve will not close tightly, thus
allowing an escape back into the
intake manifold for the gas when
compression commences. Carbon,
around the exhaust valve will offer
| just as good an escape. the only
difference being that the gas vapor
goes out through the exhaust and
thus represents a double loss 1t
can never be used again in the same
engine.
1t is also evident that If either
one of these valves happen to
stick open during the cranking
process the yapor will escape
rapidly, thus reducing the COM
preston to a point where the pis-
ton, in travelling upward on its
compression stroke, will show
scarcely any resistance. Whether
or not this is the case can be
determined by removing the valve
cover plates and noting the posi-
ton of the valve stems. When
the respective cylinder is under
compression both valves should be
closed, a position in which there
should be no noticeable clearance
between the valve tappets and the
end Of the valve stems other than
normal clearance.
While in an engine that has had
attention for several months this
clearance may be greater than the
thickness of q visiting card or
whatever guide the reference book
for the particular make of car
recommends, extra clearance may
be normal for the particular con.
dition of the engine If the same
is found to be the case with the
valves for the other cylinder.
Lung Leakage.
Excessive valve clearance all
around indicates that all valves
are not seating tightly. This
means lung leakage" and conse-
quent waste of. power To give
the lung test" to best advantage
1t Is important to do the hand
cranking after the engine has been
thoroughly warmed up, for the
test should show how the power
plant breathes when 1t is running
normally, not when CONCEALED oil
and contracted parts are likely to
mislead the owner. Valves that
show too much clearance when
cold may show too little when
hot. This might mean loss OF
compression during noronIal run
ming, and perhaps excessive COM
preston when cold.
In view of all these possibilities
Of leakage of vapor, however, It Is
usually not evident to the motor
list that the principal cause Of his
uneven compression may be due
to worn piston rings or cylinders
worn oval. Thus he is likely to
jump to conclusion regarding the
valves before considering q more
serious symptom.
This point calls for a little head.
work rather than physical effort.
If cylinders Nos. 3 and of q six
cylinder engine, let us say, show
excessively low compression as
compared with the normal for the
engine we may assume leakage of
vapor past the piston rings into the
crankcase. Assuming this 1t Is
also fair to presume that there
would be q reverse leakage from
crankcase to cylinders, which would
mean that in Nos. 8 and spark
plugs should foul more readily than
those In the other four cylinders.
If the motorist has kept records
Of supplies purchased for the car,
and IL this condition be trne,
he will find that his oil consump-
ton has increased a little. There
may also be undue smoking either
from the exhaust or breather tube,
or both. There may be a piston
slap in the engine.
II so, he has doubtless discovered
through the test that his cylinders
need reboring or, in any case, that
new rings are needed. But II, on
the other hand, no such symptoms
are observed, he is justified In
suspecing that valves need regrintl-
ing.
In test of this sort it Is very
important to see that the spark
plug Of the cylinder being in
spected is tight and the respec.
tive pet cock does not leak. To
make the test without taking these
precautions would be like testing
a mans lung capacity with a leak
in the apparatus.
There is no harm done II the
lung test" for the engine fails to
lead the owner to any conclu-
sions regarding the condition If his
power plant. But that is the beauty
Of 1t. He cannot help but learn