Valve Lash A D Ju Stm E N Ts - GMC 4000 Series Service Manual

Sec. 6A
Page 262
GASOLINE ENGINES
Figure 13— Cylinder H ead Bolt Tightening
Sequence for In-Line Engine
2. Visually inspect ventilation valves for ac­
cumulation of sludge or other matter at inlet
opening (fig. 12).
3. If valves appear to be in good condition,
start engine and allow to run at idle speed. Con­
nect tachometer if engine is not so equipped.
4. With engine running, note tachometer read­
ing; then cap the inlet openings in valves and com­
pare tachometer reading with reading previously
noted before capping openings in ventilation valves.
If there is a change of le s s than 50 rpm when the
valve openings are closed, a malfunction of one or
both of the valves is indicated.
VENTILATION VALVE REPLACEMENT
1. Use socket wrench to remove valves from
engine.
2. If valves have been in use le ss than 12
months or le ss than 12,000 m iles, solvent may be
used to clean the valves.
IMPORTANT NOTE: Crankcase ventilation
valves (P.C.V.) MUST be replaced every 12 months,
or at 12,000-m ile intervals, whichever occurs
first. Also, replace ventilation hoses and/or clamps
if not in good condition.
3. Install valves in threaded ports in cylinder
heads, then install rocker arm covers.
4. At service intervals the breather cap and
Figure 1 4 — U se of O il Deflector Clips
on In-Line E n g in e ((Typical)
G M C S E R V I C E M A N U A L
hose must be inspected, cleaned, and reassembled,
to ensure free flow of air from air cleaner into
valve rocker arm cover.
CYLINDER HEAD BOLT TORQUE AND
quired unless a leak is suspected, or in case head
gasket has been replaced. Valve lifters which are
hydraulic type should be reset to place lifter plung­
er near center of travel, after cylinder head bolts
have been retorqued.
dicated in figure 13. Correct torque is 95 foot­
pounds.
temperature is reached. Oil deflector clips (fig.
14) may be installed on rocker arm s to prevent oil
spatter while adjusting valve lifters.
rocker arm stud nut at one rocker arm until it be­
gins to clatter, then turn stud nut backdown slowly
until the clatter just stops. This is zero lash posi­
tion.
until engine runs smoothly. Repeat additional %
turns and 10-second pauses until stud nut has been
turned down 1 full turn from zero lash position.
arm stud nut is necessary to allow lifter to adjust
itself and allow valve to completely close each
time. If valve is held open, the top of piston may
strike valve and cause internal damage and/or bent
push rod. Noisy valve lifters should be replaced.
arm cover using new gasket.
Figure 15— Cylinder Head Bolt Tightening
Sequence on V6 Engine
VALVE LASH ADJUSTMENT
(IN-LINE 6 CYLINDER ENGINE)
Checking cylinder head bolt torque is not re­
1. Tighten cylinder head bolts in sequence in­
2. Start engine and run until normal operating
3. With engine running at idle speed, back off
4. Turn nut down % turn and pause 10 seconds
NOTE: The gradual turning down of rocker
4. Adjust rest of valve lifters in same manner.
5. Remove deflector clips and install rocker