GMC 4000 Series Service Manual page 274

CYLINDER HEAD BOLT TORQUE A N D
VALVE LASH ADJUSTMENT
(V6 ENGINE)
A check of cylinder head bolt torque should be
made at regular tune-up intervals on V6 engines,
and should be followed by valve lash adjustment.
Follow procedure given below to tighten cylinder
head bolts and adjust valve lash.
1. Run engine until normal operating tem per­
ature is reached, then stop engine and remove
rocker arm covers.
2. Using torque wrench, loosen, then tighten
cylinder head bolts in sequence shown in figure 15.
Correct head bolt torque is 60 to 65 foot-pounds.
NOTE: Adapter (J-8514) may be used to torque
cylinder head bolts under the rocker arm shaft.
3. Using feeler gauge and box end wrench
(fig. 16), set exhaust valve clearance at 0.018-inch
and intake valve clearance at 0.012-inch.
4. While performing above operations, observe
ENGINE MODELS
Without Exhaust Emission Control
IDLE*
RPM
With Exhaust Emission Control
Without Exhaust Emission Control
IGNITION
TIMING**
With Exhaust Emission Control
* With air condition turned on (when used).
** With vacuum advance line disconnected and plugged.
Note: Above timing settings apply when average Nation-Wide regular fuel is used.
Refer to Next Page For "Engine Tune-Up Specifications."
G M C S E R V I C E M A N U A L
Figure 17— Engine Idle Speed RPM and Timing Data Chart
Figure 16— Adjusting Valve Clearance
the oil supply to valve rocker arms. If there ap­
pears to be insufficient lubrication, make neces­
sary corrections to provide adequate oil supply.
250 - 292 305E - 305C
525 550
700 550
/2°
4°
t
0°
T /°
Sec. 6A
Page 263
GASOLINE ENGINES
351C - 351M
550
550
10°