Minimum Compression Pressure at 600 rpm
Air density at 500 ft. altitude based on 85° F (29.4° C) and 29.38 in Hg (99.49 kPa) wet barometer.
Perform Steps 2 through 5 on each cylinder. The
compression pressure in any one cylinder at a given
altitude above sea level should not be less than the
minimum shown in Table 1. In addition, the variation in
compression pressures between cylinders must not
exceed 25 psi (172 kPa) at 600 rpm.
EXAMPLE: If the compression pressure readings were
as shown in Table 2, it would be evident that No. 3
between the fuel inlet and return manifold connectors.
cylinder should be examined and the cause of the low
This will permit fuel from the inlet manifold to flow
compression pressure be determined and corrected.
directly to the return manifold.
The pressures in Table 2 are for a 71E engine operating
Start the engine and run it at a 600 rpm.
at an altitude near sea level. Note that all of the
Observe and record the compression pressure indicated
cylinder pressures are above the low limit for
on the gage. Do not crank the engine with the starting
satisfactory engine operation. Nevertheless, the No. 3
motor to obtain the compression pressure.
cylinder compression pressure indicates that something
unusual has occurred and that a localized pressure leak
Low compression pressure may result from any one of
A. Piston rings may be stuck or broken. To
determine the condition of the rings, remove the
air box cover and inspect them by pressing on
the rings with a blunt tool (Fig. 3). A broken or
stuck ring will not have a "spring-like" action.
B. Compression pressure may be leaking past the
cylinder head gasket, the valve seats, the
injector tube or a hole in the piston.
Fig. 2 - Checking Compression Pressure