GMC 4000 Series Service Manual page 304

2. Referring to ENGINE FUEL SYSTEM (SEC.
6M) in this manual, service air cleaners and fuel
filters. Also, check operation of accelerator con­
trol linkage for free movement. Check operation of
engine stop mechanism which must function per­
fectly.
3. Check engine idle speed which should be
625 rpm. The hex head, self-sealing, adjusting
screw at rear of fuel injection pump is provided
for setting slow idle speed. Adjustment is made by
turning the screw in with wrench (fig. 4) to increase
idle speed. Turn screw out (counterclockwise) to
reduce idle speed.
NOTE: If after the foregoing procedures have
been completed, the engine performance is not
satisfactory, it may be necessary to remove the
fuel injection nozzles and check the nozzle opening
pressure and spray pattern. Instructions for serv­
icing injection nozzles are covered later in EN­
GINE FUEL SYSTEM (SEC. 6M) of this manual.
FUEL INJECTION PUMP TIMING
A check of fuel injection pump timing is not
normally required as part of engine tune-up pro­
cedure; however, in cases when it is necessary to
check the timing in diagnosing trouble, refer to
"Checking Injection Timing," covered later in
ENGINE FUEL SYSTEM (SEC. 6M) for information
on making the timing check.
CHECKING ENGINE VALVE TIMING
Valves must open and close in correct rela­
tionship to upper and lower-dead-center of crank­
shaft as indicated in valve timing as indicated in
"Tune-up Specifications" later in this manual.
When a check of valve timing is necessary, follow­
ing procedure may be used referring to markings
at crankshaft damper for determining top-dead-
center on No. 1 cylinder.
1. Remove left-hand rocker arm cover from
cylinder head to provide access to rocker arms at
No. 1 cylinder.
2. Turn engine clockwise (viewed from front
of engine) to "UDC" mark at crankshaft damper on
compression stroke. Both the intake and the ex­
haust valve on No. 1 cylinder will then be closed.
3. Adjust valve lash on No. 1 exhaust valve
(front valve) to exactly 0.054 inch.
4. Turn engine clockwise until No. 1 exhaust
valve opens and begins to close, then with fingers
try turning push rod of No. 1 exhaust valve as en­
gine is cranked slowly. When push rod rotates with
finger pressure, the "UDC" markon damper should
be at pointer. This will be about 1 revolution from
starting point. If push rod starts to rotate at any
point within one-quarter inch either side of "UDC"
G M C S E R V I C E M A N U A L
1 Camshaft Gear
2 Injection Pump D rive
3 D rive Gear Bolts
4 Self Locking Bolt
5 Camshaft Gear
Lock Plates
6
7 Balance Shaft Idler
mark, the valve timing is correct. Be sure to ad­
just exhaust valve clearance to 0.018 inch after
performing the foregoing check.
starts to rotate at a point more than three-quarters
inch either side of the "UDC" mark, the camshaft
can be considered "out-of-time."
and engine front cover assembly must be removed;
then the timing gear teeth must be meshed accord­
ing to marks (A, B, C, and D, fig. 5) on gears.
to ENGINE FUEL SYSTEM (SEC. 6M) for instruc­
tions when removing, installing and timing the fuel
injection pump assem bly.
Chart."
TORO-FLOW DIESEL ENGINE
Balance Shaft Thrust
8
Gear
9 Balance Shaft Gear
10 Gear Retainer Plate
11 Plate Retaining Bolts
12 Crankshaft Balancer
Retainer
13 Cylinder Block
14 Camshaft Idler Gear
Gear
Figure 5 — Gear Train and Timing Marks
(Engine Front Cover Removed)
5. If when checking valve timing, the push rod
To correct the timing, the fuel injection pump,
If a change in valve timing is necessary, refer
Refer to following page for "Engine Tune-Up
Sec. 6B
Page 293
Plate
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