Figure 2. Fuel Pump Valving and Rotation (Right Hand Pump Shown).
and the suction side of the pump, which prevents building up any fuel oil pressure around the shaft ahead of the
Some fuel oil seepage by the fuel pump seals can be expected, both with a running engine and immediately
after an engine has been shut down. This is especially true with a new fuel pump and/or new pump seals, as
the seals have not yet conformed to the pump drive shaft. Fuel pump seals will always allow some seepage.
Tapped holes in the pump body are provided to prevent fuel oil from being retained between the seals.
Excessive fuel retention between the seals could provide enough pressure to cause engine oil dilution by fuel,
therefore, drainage of the excess fuel oil is mandatory. However, if leakage exceeds one drop per minute,
replace the seals. The drive and driven gears are a line-to-line to a 0.001-inch press fit on their shafts. The
drive gear is provided with a gear retaining ball to locate the gear on the shaft.
A spring-loaded relief valve incorporated in the pump body normally remains in the closed position, operating
only when pressure on the outlet side (to the fuel filter) reaches approximately 65 psi (448 kPa).
In operation, fuel enters the pump on the suction side and fills the space between the gear teeth which are
exposed at that instant. The gear teeth then carry the fuel oil to the discharge side of the pump and, as the
gear teeth mesh in the center of the pump, the fuel is forced out into the