GMC 4000 Series Service Manual page 280

garden hose approximately four feet in length.
Place one end of the hose near the end of each in­
take and exhaust valve with the other end of the
hose to the ear. In this manner, the sound is local­
ized 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 caus­
ing abnormal 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 in­
dication of insufficient oil supply, or improper
adjustment.
4. Intermittent Clicking - Probable 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.
REMOVAL
1. Remove valve mechanism as previously
directed.
2. Mark distributor housing, with chalk, at
each cylinder position (plug wire), then disconnect
plug wires at sparkplugs and coil and remove dis­
tributor 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 original locations.
G M C S E R V I C E M A N U A L
INSTALLATION
installed, coat foot of valve lifters with Molykote
or its equivalent.
and torque screws to ''Specifications."
number one cylinder position, then connect prim ­
ary lead at coil.
speed and mixture.
directed.
rod on the cylinder(s) to be serviced.
hole to hold the valves in place.
necting air supply to spark plug hole now is avail­
able to facilitate the valve spring replacement.
valve spring, remove the valve locks, valve cap (or
rotator), valve shield and valve spring and damper.
er, valve shield and valve cap (or rotator) in place.
The close coiled end of the spring is installed
against the cylinder head. Compress the spring
with Tool (J-5892) and install oil seal in the lower
GASOLINE ENGINES
\
Figure 2 0 — U sing Special Tool and Compressed
Air to Remove Valve Spring
1. Install valve lifters.
NOTE: Whenever new valve lifters are being
2. Install push rod covers, using new gaskets,
3. Install distributor, positioning rotor to
4. Install and adjust valve mechanism.
5. Adjust ignition timing and carburetor idle
VALVE STEM OIL SEAL AND/OR
VALVE SPRING REPLACEMENT
1. Remove rocker arm cover as previously
2. Remove spark plug, rocker arm, and push
3. Apply com pressed air to the spark plug
NOTE: An adapter (J-21546) for use in con­
4. Using Tool (J-5892) (fig. 20) to compress the
5. Remove the valve stem oil seal.
6. To replace, set the valve spring and damp­
Sec. 6A
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