The Washington herald., 1921-05-22
DECREASED ENGINE
POWER RESULTS IN
BAD PERFORMANCE
Time-Honored Method Of
Testing Compression by
Z Hand Cranking.
MUST STAND HEAT
Full Outline Is Given of Cure
And Causes of Poppet
Trouble.

When poppet valves do not func-
tion properly due to warped heads,
pitted faces, bent stems, worn stems.
etc, there s a considerable fallins
OF in the power developed BY the
engine and the owner Immediately
discovers II in the form OF poor per-
formance. The time-honored meth
cd of testing the compression oy
crankfng the engine by hand slowly
to determine the relative resistance
offered is a fairly satisfactory way
Of determining compression loss. but
does not indicate where that loss
exists The owner of . car should
bear in mind that valve heads work
in an extremely hot atmosphere,
since the heads are in the comous-
tfon chamber and consequently are
exposed to the flame OF the explo-
sions. They must therefore be able
TO withstand the terrific heat With
out warping, because II they should
warp the effectiveness OF the valve
to make a perfect joint with its seat
would at once be destroyed The
reason car manufacturers state tnat
.-valves are surrounded by adequate
water space" is because they wish
to show that the valves being prop
erly cooled are not likely to be af-
fected quickly by the heat In some
engines where provision has not
been made for the proper cooling OF
Ne valves the engines give contin>
tal trouble from loss of compress
sion. valves sticking. valves requir-
ing frequent grinding, misnring
due to irregularities in the valve
action, etc
should Remove Valve.
The only safe way an owner can
tell whether a valve head is warped
or badly pitted or a stem bent or
badly carbonized is to remove the
valve, examine it and measure it
whilA the compression test is all
right to check losses due to poor
valve seating, it must be determined
that there is no leakage elsewhere
as, for example, around the cylinder
head Joint or valve plugs, IL such
be used, or past poorly fitting pis-
tons or rings, or due to worn cylin-
ders, etc
After a valve is removed by means
of a valve spring compressor per
unitting, it should first be carefully
cleaned by submersion in kerosene,
then wiped with a clean CLOTH Ex-
anime the face of the valve for
small black spots. Place the valve
upright on a level surface and meas
ure four or five distances from head
To plate This will give you a good
check on the trueness of the head
A variation that can be measured
with an ordinary rule may be taken
as being enough to cause poor valve
seating, hence leakage of mixture
past the valve when II Is closed A
valve with a warped bead should be
replaced
Testing of Stems
Test the stem for straightness.
Place the stem on a level plate,
while the head of the valve hangs
over the edge of the plate. The
eye can instantly detect if the stem
is not straight II it is bent a lit
tie it may be Strengthened in a wise.
A bent stem may cause the valve
to stick open, or it also may cause
it to return to its seat too slowly.
II the valve stem is straight 1t
should be checked for diameter.
The best way to do this is first to
polish the stem with a piece of
emery cotton cloth and then try it
in its particular guide. Place 1t in
the guide (when the tappet is all
the way DOWN., and holding one
hand on the stem and the other on
the head (to force the valve against
its seat) feel for side play. There
should be none perceptible. II the
valve stem can be shaken in it's
guide it will allow oil to leak down
and air to leak up. Some of you
may notice that there is oil all
around the valve springs and the
tappets and on the side of the en-
gine on which the valves are To-
Gated That oil usually comes out
through the valve guides, which, by
the way, may themselves be worn.
1t is possible in some cases where
detachable guides are used to in
stall a new guide to fit the worn
stem, but where this construction
Is not used a valve with an over
size stem must be obtained and
ntted to the guide. 1t should be
just free enough so 1t falls to its
seat after being fitted about an
inch
At the same time that the valves
are tested for the defects mentioned
the valve springs should be meas
ured and examined. A weak spring
Is likely to cause a lot of trouble.
Place the spring on a level place
and with the eye notice IL 1t is out
Of shape or smaller than any of the
others Usually you can stretch
and bend the spring so it will re-
turn to its normal shape, but where
the spring temper is lost bending
does not prevent the spring from
falling into almost any position
when in use. II a spring is known
to be weak because of weakened
metal the best thing to do is to
get new spring. or as a tenn
porary measure put a lot Of wash
ers under IL to compress Il still