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Cylinders
FIGURE 16-8. DIFFERENTIAL PRESSURE TESTER CALIBRATION
WARNING
To prevent possibility of serious bodily injury
or death, before moving the propeller
accomplish the following:
a. Disconnect all spark plug leads.
b. Verify magneto switches are
connected to magnetos, that they are
in the "OFF" Position and "P" leads
are grounded.
c. Throttle position "CLOSED."
d. Mixture control "IDLE-CUT-OFF."
e. Set brakes and block aircraft wheels.
f. Insure that aircraft tie-downs are
installed and verify that the cabin
door latch is open.
g. Do not stand within the arc of the
propeller blades while turning the
propeller.
(1) Perform the test as soon as possible after the
engine is shut down to insure that the piston
rings, cylinder walls, and other engine parts are
well lubricated and at operating conditions.
16-8
(2) Turn the crankshaft by hand in the direction of
rotation until the piston, in the cylinder being
checked, is coming up on its compression stroke.
(3) Install an adapter in the spark plug hole and
connect the calibrated differential pressure tester
to the adapter. (NOTE: Cylinder pressure valve
is in the Closed position). Slowly open the
cylinder pressure valve and pressurize the
cylinder, not to exceed 20 pounds per square
inch. Continue rotating the engine against this
pressure until the piston reaches top dead center.
Reaching top dead center is indicated by a flat
spot or sudden decrease in force required to turn
the crankshaft. If the crankshaft is rotated too
far, back up at least one-half revolution and start
over again to eliminate the effect of backlash in
the valve operating mechanism and to keep the
piston rings seated on the lower ring lands. This
is critical because the slightest movement breaks
this piston ring sealing and allows the pressure
to drop.
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