the gears apart, resulting in undue wear
Description
on the gears, shaft, body and cover.
The positive displacement gear-type fuel
T w o oil seals are pressed into the bore in
pump (Figure 11C-49) transfers fuel
the flanged side of the pump body to re-
from
the
supply
tank
to
the
fuel
tain the fuel oil in the pump and the lu-
injectors. The pump circulates an ex-
bricating oil in the blower timing gear
cess supply of fuel through the injectors
compartment (see Figure 11C-52 on page
which purge the air from the system and
11C-30). The oil seals are installed with
cools the injectors. The unused portion
the lips of the seals facing toward the
of fuel returns to the fuel tank by means
flanged e n d o f t h e p u m p b o d y . A s m a l l
of a fuel return manifold and fuel return
hole "E" (Figure 11C-51 on page 11C-29)
line.
serves as a vent passageway in the
body, between the inner oil seal and the
The fuel pump is attached to the rear
suction side of the pump, which prevents
end plate cover of the blower assembly
building up any fuel oil pressure around
with three nylon patch bolts which pre-
the shaft ahead of the inner seal.
vent the oil in the blower cover from
seeping out around the bolt threads.
Some fuel oil seepage by the fuel pump
The pump is driven off the end of the
seals can be expected, both with a run-
blower lower rotor by means of a drive
ning engine and immediately after an en-
coupling fork attached to the end of the
gine
has
been
shut
down.
This
is
pump drive shaft and mating with a drive
especially true with a new fuel pump
disc attached to the blower rotor as
and/or new pump seals as the seals have
s h o w n in Figure 11C-50 on page 11C-29.
not yet conformed to the pump drive
shaft. Fuel pump seals will always allow
The fuel pump cover and body are posi-
some seepage. Tapped holes in the pump
tioned by two dowels. The dowels aid in
body are provided to prevent fuel oil
maintaining gear shaft alignment. The
from being retained between the seals.
mating surfaces of the pump body and
Excessive fuel retention between the
cover are perfectly fiat ground surfaces.
seals could provide enough pressure to
No gasket is used between the cover and
cause engine oil dilution by fuel, there-
body since the pump clearances are set
fore, drainage of excess fuel oil is
up
on
the
basis
of
metal-to-metal
mandatory. However, if leakage exceeds
contact. A very thin coat of sealant
one drop per minute, replace the seals.
provides a seal against any minute irreg-
ularities
in
the
mating
surfaces.
The drive and driven
Cavities in the pump cover accommodate
line-to-tine to 0.001" press fit on their
the ends of the drive and driven shafts.
shafts.
The
drive
gear
is
provided
with
a gear retaining ball to locate the gear
The fuel pump body is recessed to pro-
on the shaft (see Figure 11C-50 on page
vide running space for the pump gears
(see Figure 11C-51 on page 11C-29).
Recesses are also provided at the inlet
and outlet positions of the gears. The
A spring loaded relief va ve incorporated
small hole "A" permits the fuel oil in the
in the pump body normally) r e m a i ns in the
inlet side of the pump to lubricate the re-
closed position, operating only when
lief
valve
at
its
outer
end
and
to
pressure on the outlet side (to the fuel
eliminate the possibility of a hydrostatic
filter). reaches approximately 65 psi (448
lock which would render the relief valve
kPa).
inoperative. Pressurized fuel contacts
the relief valve through hole "B" and
provides for relief of excess discharge
Operation
pressures. Fuel reenters the inlet side
In operation, fuel enters the pump on
of the pump through hole "C" when the
the suction side and fills the space be-
discharge pressure is great enough to
tween the gear teeth which are exposed
move the relief valve back from its seat.
at that instant. The gear teeth then
Part of the relief valve may be seen
carry the fuel oil to the discharge side of
through hole "C". The cavity "D" pro-
the pump and, as the gear teeth mesh in
vide escape for the fuel oil which is
the
center
of
the
pump,
the
fuel
is
squeezed out of the gear teeth as they
forced out into the outlet cavity. Since
mesh together on the discharge side of
this is a continuous cycle and fuel is
the pump. Otherwise, fuel trapped at
continually being forced into the outlet
the root of the teeth would tend to force
