GMC 4000 Series Service Manual page 388

2. Place upper O-ring seal in groove in hy­
draulic head (fig. 36).
3. Position the hydraulic head assembly so
the locating slot in head block is aligned with head
locating screw; and turn face gear so that timing
mark on gear is aligned with mark on housing (fig.
36). Carefully insert head assembly into housing
bore. Observe face gear through the pump housing
opening as head is pushed down into place. Teeth
on face gear must mesh with drive gear teeth.
4. Install head locating screw with copper
gasket and index plate (fig. 36), and if necessary,
rotate head assembly so the locating screw can be
turned freely - indicating no interference. Tighten
locating screw to to
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5. Place a hydraulic head retainer and a socket
head s c r e w in diagonally o p p o site c o r n e r s of the
housing. Gradually tighten the retainer screws
until head is properly seated, then install remain­
ing two retainers and socket head screw s. Use a
torque wrench and adapter to tighten all socket head
screw s to 13 to 15 foot-pounds torque.
. Refer to applicable instructions given pre­
6
viously under ''Control Unit Assembly Replace­
ment" and install the control unit assembly.
7. Referring to "High P ressure Fuel Line In­
stallation" covered previously in this section in­
stall the fuel lines between hydraulic head outlet
ports and fuel injection nozzles.
. Prime the fuel system using one of the
8
methods described under "Priming Fuel System."
9. Install equipment which may have been re­
moved to gain access to the injection pump assem ­
bly. After engine is started, inspect for fuel leak­
age, particularly at hydraulic head and high p res­
sure fuel lines.
FUEL INJECTION PUMP ASSEMBLY
NOTE: The fuel injection pump assembly is
available for service replacement as a complete
assembly; however, before pump replacement, it
is important that a complete diagnosis of problem
be made, and remedial measures taken, as pre­
viously explained under "Fuel Injection System
Trouble Diagnosis." In most instances the required
repairs may be made without removing the injec­
tion pump assembly from the engine.
FUEL INJECTION PUMP
REPLACEMENT
The paragraphs following include directions
for replacement of the fuel injection pump assem ­
bly, but replacement should only be made in case
the symptoms described in "Fuel System Trouble
Diagnosis Chart" in this section definitely indicate
that the fuel injection pump assembly is at fault
G M C S E R V I C E M A N U A L
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
foot-pounds torque.
1 1
and is not repairable without removing the unit
from the engine:
Before beginning the removal of fuel injection
pump, either for overhaul of other engine compon­
ents or for installation of a replacement pump a s­
sembly, the following equipment should be on hand:
1. Dust caps and plugs, which are available
in a kit, for closing the openings at injection noz­
zles and ports in hydraulic head after high p res­
sure lines are removed.
2. Gaskets for use when installing the fuel in­
jection pump assembly.
3. Clean shop cloths.
4. Tachometer for use when adjusting engine
idle speed and for checking governed speed.
CAUTION
DO NOT attempt to work on the fuel
injection pump, nozzles, or high pressure
lines in a dusty area. Extreme precau­
tions must be taken to prevent any dust
particles from entering the fuel passages
in lines and nozzles. Any dirt or abrasive
material permitted to enter the fuel sup­
ply port on fuel injection pump could quick­
ly cause extensive damage to, or possibly
ruin the pump hydraulic head mechanism.
REMOVAL
Depending on type of vehicle and accessory
equipment, remove the necessary equipment to
provide access to fuel injection pump assembly,
high pressure fuel lines and engine controls. Care­
fully observe the arrangement of accelerator con­
trol linkage, and the engine stop mechanism, so
the linkage can be properly installed.
NOTE: Clean any accumulated dirt from the
entire area around fuel injection pump assembly,
upper part of engine front cover, and all fuel line
fittings.
1. Remove the cover and gasket from right
side of fuel injection pump to expose the alignment
mark in the opening below the control unit lever
(fig. ).
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2. Remove the access cover and gasket from
top of engine front cover assembly to expose point­
er ( , fig. ) and mark on injection pump hub.
8 1 0
SUGGESTION: To prevent accidental dropping
of bolt washers into engine front cover and out of
reach, pack clean shop cloths into cavity below the
gear attaching bolts. Do not crank engine until the
cloths have been removed.
3. Remove rocker arm cover from left-hand
cylinder head, then crank engine to place No. 1
piston on compression stroke - (both valves will
then be closed and push rods can be turned with
fingers). Slowly crank the engine until the "INJ"
Sec. 6M
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