GMC 1976 ZEO 6083 Maintenance Manual page 301

6A- 3 6 ENGINE
Figure 24-Checking Valve Spring
b. Observe rocker arm pad for excessive wear
or excessive off square . Replace as required . See
r'ig-
ure 25 .
c. Check for excessive valve stem to guide
clearance. If necessary, correct as required .
6. Valves Noisy Regardless of Engine Speed.
This condition can be caused by foreign particles
or excessive valve lash .
Correction :
a.
With transmission in
"park" and parking brake on, run the engine at a
moderate speed .
If this method does not quiet the lifter, strike the
rocker arm above the push-rod with a mallet while
the engine is idling . This method of correction has
proven successful for dislodging a foreign particle
which is preventing the ball from seating properly .
b. Check for valve lash by turning engine so
the piston in that cylinder is on top dead center of
firing stroke . If valve lash is present, the push-rod
can be freely moved up and down a, certain amount
with rocker arm held against valve.
Valve lash indicates one of the following:
1 . Worn push-rod .
2. Worn rocker arm.
Figure 25-Rocker Arm Wear
3. Lifter plunger stuck in down position due to
dirt or varnish.
4. Defective lifter .
Checking of the above four items:
1 . Observe upper end of push-rod . Excessive wear
of the spherical surface indicates one of the following
conditions .
a. Improper hardness of the push-rod ball .
The push-rod and rocker arm must be replaced .
b. Improper lubrication of the push-rod . The
push-rod and rocker arm must be replaced . The oil-
ing system to the push-rod should be checked.
2. If push-rod appears in good condition and has
been properly lubricated, replace rocker arm and
recheck valve lash .
3 . If valve lash exists and push-rod and rocker
arm are okay, trouble is in the lifter . Lifter should be
replaced .
REMOVAL
NOTE :
Valve lifters and push-rods should be
kept in order so they can be reinstalled in their
original position . Some engines will have both
standard and .010" oversize valve lifters, the
.010" oversize lifter is etched "O" on the side of