GMC 4000 Series Service Manual page 285

Sec. 6A
Page 274
GASOLINE ENGINES
out and remove the three flywheel-to-crankshaft
dowel pinSo Crankshaft must be turned each time a
dowel pin is removed, so next pin can be driven out
without contacting cylinder block. After removing
dowel pins, remove flywheel-to-crankshaft bolts,
then remove flywheel.
2. Clean mating surfaces on crankshaft flange
and flywheel and remove any existing burrs. P osi­
tion flywheel at crankshaft flange with dowel pins
aligned.
NOTE: If new flywheel is being installed it is
necessary to ream the dowel pin holes to assure
When it becomes necessary to make a check
of valve timing, the procedure following may be
used:
1. Remove valve rocker arm cover and push
rod front cover.
2. Loosen nut at #1 intake valve rocker arm,
swing rocker arm away from push rod, then re­
move push rod and hydraulic valve lifter.
3. Temporarily install a flat face mechanical
lifter in place of the hydraulic lifter.
4. Turn crankshaft until #2 exhaust valve
opens and notch on pulley or damper is aligned
with "O" mark on timing pointer.
5. Position dial indicator to measure lifter
movement and set indicator at zero. Turn crank­
shaft 360 degrees and read indicator. On correctly
timed engines the indicator will read as follows:
On 250 Engines . . . . 0.010 to 0.018 inch
On 292 Engines . . . . 0.012 to 0.020 inch
VALVE ROCKER A RM COVER
REPLACEMENT
REMOVAL
Remove valve rocker arm cover screws, then
remove rocker arm cover. On tilt cab models it
will be necessary to remove transmission shift
rods in order to remove cover from left-hand
cylinder head.
NOTE: If cover is stuck in place, loosen by
striking with palm of hand or a rubber mallet. Do
not pry on cover flange since the flange may be
distorted.
INSTALLATION
Using new cover gasket, install rocker arm
cover and tighten cover screws uniformly.
G M C S E R V I C E M A N U A L
correct hole alignment and dowel pin fit. Dowel
pins must be driven into place as they are inter­
ference fit.
to 110 foot-pounds torque, use reamer (J-22808)to
size and line ream the dowel pin holes. Finish
ream the holes with reamer (J-22808-1). Drive
oversize dowel pins flush with flywheel rear sur­
face. Install bearing cap and oil pan referring to
instructions previously given in this section. A s­
semble clutch mechanism, then install transm is­
sion on engine.
CHECKING ENGINE VALVE TIMING
zero and turn crankshaft 360 degrees, then read
indicator again. If reading is now in accord with
specifications, the engine is timed properly.
ings with gears properly indexed for each engine
and the indicator readings resulting from improp­
erly indexed gears:
(Cu.In.)
condition, remove engine front cover and check
for proper indexing of timing marks on gears.
IN-VEHICLE SERVICE OPERATIONS
(V6 ENGINE)
hand or left-hand cylinder head.
REMOVAL
instructions previously given.
gradually until spring pressure is fully relieved
at rocker arm s. Lift off the rocker arm shaft and
brackets, with attaching bolts, as an assembly.
manner so they can be returned to original p osi­
tion at assembly.
3. With flywheel bolts installed and tightened
If reading is not as shown, reset indicator at
NOTE: Chart following shows indicator read­
Camshaft
Engine
Part No. & Properly
Valve Lift Indexed
250 3864896-.388 .014" - .004" .0351" .0055"
292 3848000-.405 .016" - .004" .0379" .0068"
6. If foregoing check indicates an out-of-tim e
VALVE ROCKER ARMS, SHAFT,
A N D PUSH ROD REPLACEMENT
Same instructions apply to either the right-
1. Remove rocker arm covers referring to
2. Loosen rocker arm shaft bracket bolts
3. Remove push rods and identify in some
4. On all 305 engines and 351C engine, if the
Gears One One
Tooth Tooth
Adv. Ret.