Chevrolet Light Duty Truck 1973 Service Manual page 387

5. Remove rocker arm cover.
Do not pry rocker arm cover loose.
CAUTION:
Gaskets adhering to cylinder head and rocker
arm cover may be sheared by bumping end of
rocker arm cover rearward with palm o f hand
or a rubber mallet.
Installation
1. Clean gasket surfaces on cylinder head and rocker
arm cover with degreaser then, using a new gasket,
install rocker arm cover and torque to
specifications.
2. Install carburetor heater (if removed).
3. Connect temperature wire at clips on left rocker
arm cover.
4. Connect crankcase ventilation hoses (as required).
5. Install air cleaner, start engine and check for leaks.
Valve Mechanism
Removal
1. Remove rocker arm covers as outlined.
2. Remove rocker arm nuts, rocker arm balls, rocker
arms and push rods.
NOTE: Place rocker arms, rocker arm balls
and push rods in a rack so they may be
reinstalled in the same locations.
Installation and Adjustment
NOTE: Whenever new rocker arms and/or
rocker arm balls are being installed, coat
bearing surfaces of rocker arms and rocker
arm balls with "Molykote" or its equivalent.
1. Install push rods. Be sure push rods seat in lifter
socket.
2. Install rocker arms, rocker arm balls and rocker
arm nuts. Tighten rocker arm nuts until all lash is
eliminated.
3. Adjust valves when lifter is on base circle of
camshaft lobe as follows:
a. Crank engine until mark on torsional damper
lines up with center or "O " mark on the timing
tab fastened to the crankcase front cover and
the engine is in the number 1 firing position.
This may be determined by placing fingers on
the number 1 valve as the mark on the damper
comes near the "O " mark on the crankcase
front cover. If the valves are not moving, the
engine is in the number 1 firing position. If the
valves move as the mark comes up to the timing
tab, the engine is in number 6 firing position
and should be turned over one more time to
reach the number 1 position.
b. With the engine in the number 1 firing position
as determined above, the following valves may
be adjusted.
Exhaust — 1, 3, 4, 8
Intake — 1, 2, 5, 7
c. Back out adjusting nut until lash is felt at the
push rod then turn in adjusting nut until all lash
is removed. This can be determined by checking
push rod side play while turning adjusting nut
(fig. 8V). When play has been removed, turn
adjusting nut in one full additional turn (to
center lifter plunger).
d. Crank the engine one revolution until the
pointer "O" mark and torsional damper mark
are again in alignment. This is number 6 firing
position. With the engine in this position the
following valves may be adjusted.
Exhaust — 2, 5, 6, 7
Intake — 3, 4, 6, 8
4. Install rocker arm covers as outlined.
5. Adjust carburetor idle speed.
Valve Lifters
Hydraulic valve lifters very seldom require attention.
The lifters are extremely simple in design, readjustments
are not necessary, and servicing of the lifters requires
only that care and cleanliness be exercised in the
handling of parts.
Locating Noisy Lifters
Locate a noisy valve lifter by using a piece of garden
hose approximately four feet in length. Place one end of
the hose near the end of each intake and exhaust valve
with the other end of the hose to the ear. In this manner,
the sound is localized making it easy to determine which
lifter is at fault.
Another method is to place a finger on the face of the
valve spring retainer. If the lifter is not functioning
properly, a distinct shock will be felt when the valve
returns to its seat.
The general types of valve lifter noise are as follows:
1. Hard Rapping Noise—Usually caused by the
plunger becoming tight in the bore of the lifter
body to such an extent that the return spring can no
longer push the plunger back up to working
position. Probable causes are:
a. Excessive varnish or carbon deposit causing
abnormal stickiness.
b. Galling or "pick-up" between plunger and bore
of lifter body, usually caused by an abrasive
piece of dirt or metal wedging between plunger
and lifter body.
2. Moderate Rapping Noise—Probable causes are:
a. Excessively high leakdown rate.
b. Leaky check valve seat.
c. Improper adjustment.
3. General Noise Throughout the Valve Train—This
E N G I N E 6-51
LIGHT DUTY TRUCK SERVICE MANUAL