TM 5-3810-300-24&P-3
15.2 Trouble Shooting (Engine)
EXAMPLE:
If the compression
pressure readings were as shown in
Table 2, it would be evident that No. 3
cylinder should be examined and the
cause of the low compression pressure
be determined and corrected.
The pressures in Table 2 are for a 71E engine operating
at an altitude near sea level. Note that all of the cylinder
pressures are above the low limit for satisfactory engine
operation.
Nevertheless, the No.
3 cylinder
compression pressure indicates that something unusual
has occurred and that a localized pressure leak has
developed.
Fig. 2 - Checking Compression Pressure
Low compression pressure may result from any one of
several causes:
Cylinder
Gage Reading
A.
Piston rings may be stuck or broken. To determine
the condition of the rings, remove the air box cover
1
445 psi
and inspect them by pressing on the rings with a
2
440 psi
blunt tool (Fig. 3). A broken or stuck ring will not
3
405 psi
have a "spring-like" action.
4
435 psi
5
450 psi
B.
Compression pressure may be leaking past the
6
445 psi
cylinder head gasket, the valve seats, the injector
tube or a hole in the piston.
TABLE 2
Engine Out of Fuel The problem in restarting an engine
1. Start the engine and run it at approximately one half
after it has run out of fuel stems from the fact that after
rated load until normal operating temperature is reached.
the fuel is exhausted from the fuel tank, fuel is then
pumped from the primary fuel strainer and sometimes
2. Stop the engine and remove the fuel pipes from the
partially removed from the secondary fuel filter before the
injector and fuel connectors of the No. 1 cylinder.
fuel supply becomes insufficient to sustain engine firing.
3. Remove the injector and install an adaptor and
Consequently, these components must be refilled with
pressure gage (Fig. 2) from Diagnosis Kit J 9531-01.
4. Use one of the fuel pipes as a jumper connection
between the fuel inlet and return manifold connectors.
This will permit fuel from the inlet manifold to flow directly
to the return manifold.
5. Start the engine and run it at a 600 rpm. Observe
and record the compression pressure indicated on the
gage. Do not crank the engine with the starting motor to
obtain the compression pressure.
6. 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 at 600 rpm.
Fig. 3 Inspecting Piston Rings
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