Chevrolet 10 Series 1968, Service Manual, Page: 362 / 713

ENGINE 6-15
Installation and Adjustment
NOTE: Whenever new rocker arms and/or
rocker arm balls are being installed, coat bear­
ing 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 cam­
shaft lobe as follows:
a. Mark distributor housing, with chalk, at each
cylinder position (plug wire) then disconnect plug
wires at spark plugs and coil and remove distrib ­
utor cap and plug wire assembly (if not previ­
ously done).
b. Crank engine until distributor rotor points to
number one cylinder position and breaker points
are open. Both valves on number one cylinder
may now be adjusted.
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. 2L). When play has been removed, turn ad­
justing nut in one full additional turn (to center
lifter plunger).
d. Adjust the remaining valves, one cylinder at a
time, in the same manner.
4. Install distributor cap and spark plug wire assembly.
5. Install rocker arm cover as outlined.
6. Adjust carburetor idle speed and mixture.
Valve Lifters
Hydraulic valve lifters very seldom require attention.
F ig . 2 L —V a lv e Adjustment
The lifters are extremely simple in design, readjust­
ments are not necessary, and servicing of the lifters
requires only that care and cleanliness be exercised in
the handling of parts.
Locating N oisy 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 ab­
normal stickiness.
b. Galling or “ pickup” 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
will, in almost all cases, be a definite indication of
insufficient oil supply, or improper adjustment.
4. Intermittent Clicking ^ P ro b a b le causes are:
a. A microscopic piece of dirt momentarily caught
between ball seat and check valve ball.
b. In rare cases, the ball itself may be out-of-round
or have a flat spot.
c. Improper adjustment.
In most cases, where noise exists in one or more
lifters all lifter units should be removed, disassembled,
cleaned in a solvent, reassembled, and reinstalled in the
engine. If dirt, varnish, carbon, etc. is shown to exist in
one unit, it more than likely exists in all the units, thus
it would only be a matter of time before all lifters caused
trouble.
Removal
1. Remove valve mechanism as outlined.
2. Mark distributor housing, with chalk, at each cylin­
der position (plug wire) then disconnect plug wires
at spark plugs and coil and remove distributor cap
and plug wire assembly.
3. Crank engine until distributor rotor points to number
one position, then disconnect distributor primary
lead at coil and remove distributor.
4. Remove push rod covers (discard gaskets).
5. Remove valve lifters.
NOTE:
Place valve lifters in a rack so they
may be reinstalled in the same location.
Installation
1. Install valve lifters.
NOTE:
Whenever new valve lifters are being
CHEVROLET TRUCK SERVICE MANUAL