DETROIT DIESEL 53
The positive displacement gear type fuel pump (Fig. 1.)
transfers the fuel from the supply tank to the fuel
injectors. The pump circulates an excess supply of fuel
through the injectors which purges the air from the
system and cools the injectors. The unused portion of
fuel returns to the fuel tank by means of a fuel return
manifold and fuel return line.
The fuel pump is mounted on the flywheel housing and
is driven by the accessory drive gear.
The fuel pump cover and body are positioned by means
of two dowels. The dowels aid in maintaining gear shaft
alignment. The mating surfaces of the pump body and
cover are perfectly flat ground surfaces. No gasket is
used between the cover and body since the pump
clearances are set up on the basis of metal-to-metal
Fig. 1. - Typical Fuel Pump Assembly
contact. A very thin coating of sealant provides a seal
against any minute irregularities in the mating surfaces.
Cavities in the pump cover accommodate the ends of
compartment (Fig. 1.). The oil seals are installed with
the drive and driven shafts.
the lips of the seals facing toward the flanged end of the
pump body. A small hole "E" (Fig. 2.) serves as a vent
The fuel pump body is recessed to provide running
passageway in the body, between the inner oil seal and
space for the pump gears (Fig. 2.). Recesses are also
the suction side of the pump, which prevents building up
provided at the inlet and outlet positions of the gears.
any fuel oil pressure around the shaft ahead of the inner
seal. Two tapped holes in the under side of the pump
The small hole "A" permits the fuel oil in the inlet side of
body, between the oil seals, furnish a means of
the pump to lubricate the relief valve at its outer end
attaching tubing for draining off any leakage.
and to eliminate the possibility of a hydrostatic lock
which would render the relief valve inoperative.
The drive and driven gears are a line-to-line to a .001"
Pressurized fuel contacts the relief valve through hole
press fit on their shafts. The drive gear is provided with
"B" and provides for relief of excess discharge
a gear retaining ball to locate the gear on the shaft.
pressures. Fuel re-enters the inlet side of the pump
through hole "C" when the discharge pressure is great
A spring-loaded relief valve incorporated in the pump
enough to move the relief valve back from its seat. Part
body normally remains in the closed position, operating
of the relief valve may be seen through hole "C" The
only when pressure on the outlet side (to the filter)
cavity "D" provides escape for the fuel oil which is
reaches approximately 65 psi.
squeezed out of the gear teeth as they mesh together on
the discharge side of the pump. Otherwise, fuel trapped
at the root of the teeth would tend to force the gears
apart, resulting in undue wear on the gears, shafts, body
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
Two oil seals are pressed into the bore in the flanged
fuel oil to the discharge side of the pump and, as the
side of the pump body to retain the fuel oil in the pump
gear teeth mesh in the center of the pump, the fuel oil is
and the lubricating oil in the blower timing gear
forced out into the outlet cavity. Since this is a
continuous cycle and fuel is continually being forced into
the outlet cavity, the fuel flows from the outlet cavity into
the fuel lines and through the engine fuel system under
The pressure relief valve relieves the discharge
pressure by by-passing the fuel from the outlet side of
1970 General Motors Corp.
SEC. 2.2 Page 1