TM 5-3895-359-14&P
Fig. 2 - Typical Fuel Pump Mounting and Drive
A spring-loaded relief valve incorporated in the pump
However, a standard pump may be reworked for use in
body normally remains in the closed position, operating
such applications by removing the two oil seals and
only when pressure on the outlet side (to the fuel filter)
installing new seals with the lips facing away from each
reaches approximately 65 psi (448 kPa).
other.
Some fuel oil seepage by the fuel pump seals can be
Operation
expected, both with a running engine and immediately
after an engine has been shut down. This is especially
In operation, fuel enters the pump on the suction side
true with a new fuel pump and/or new pump seals, as
and fills the space between the gear teeth which are
the seals have not yet conformed to the pump drive
exposed at that instant. The gear teeth then carry the
shaft. Fuel pump seals will always allow some seepage.
fuel oil to the discharge side of the pump and, as the
Tapped holes in the pump body are provided to prevent
gear teeth mesh in the center of the pump, the fuel is
fuel oil from being retained between the seals.
forced out into the outlet cavity. Since this is a
Excessive fuel retention between the seals could
continuous cycle and fuel is continually being forced into
provide enough pressure to cause engine oil dilution by
the outlet cavity, the fuel flows from the outlet cavity into
fuel, therefore, drainage of the excess fuel oil is
the fuel lines and through the engine fuel system under
mandatory. However, if leakage exceeds one drop per
pressure.
minute, replace the seals.
The pressure relief valve relieves the discharge
Effective with engines built November, 1979; a higher
pressure by by-passing the fuel from the outlet side of
temperature material lip type seal is now being used in
the pump to the inlet side when the discharge pressure
the fuel pumps. The new fuel pump seal is made of a
reaches approximately 65 to 75 psi (448 to 517 kPa).
polyacrylate material, whereas the former seal is made
of nitrile. The new fuel pumps (with the polyacrylate
The fuel pump should maintain the fuel pressure at the
seals) will have the seals installed the same as the high
fuel inlet manifold as shown on Page 10-9-6.
lift fuel pumps, with the lips of the seals facing in the
opposite direction of each other (Fig. 4). The former
Remove Fuel Pump
fuel pumps have the nitrile seals installed with both seal
lips facing the mounting flange end of the pump. Both
1. Disconnect the fuel lines from the inlet and outlet
the polyacrylate and nitrile seals are interchangeable in
openings of the fuel pump.
a fuel pump. Only the polyacrylate seals and fuel
pumps with polyacrylate seals will be serviced.
2. Disconnect the drain tube from the fuel pump.
The drive and driven gears are a line-to-line to .001"
press fit on their shafts. The drive gear is provided with
a gear retaining ball to locate the gear on the shaft (Fig.
10-3-30
