GMC S Series 1994, Repair Manual

Page: 345 / 919

VALVE AND SPRING ASSEMBLY
Assemble
*
1. Valves.
Measure
• Valve run-out. Apply a cjab of prussian blue
on the entire valve face. Seat the valve but do
not rotate it. The prussian blue traces
transferred to the valve seat are an indication
of concentricity of the valve seat.
• Clean all traces of prussian blue. Apply a dab
of prussian blue on the valve seat and repeat
the check. The traces of prussian blue
transferred to the valve face indicates valve
face concentricity. Recondition valve seat or
replace valves, if required.
2. Valve stem oil seals.
• If oversize valves have been installed,
oversized valve stem seals must be used.
• Fully seat the seals on the valve guides.
3. Spring seat, spring and cap.
4. Using J 8062, compress valve spring.
5. Valve keys.
Important
• Make sure the keys seat properly in the upper
groove of the valve stem. Grease may be used
to hold the keys in place while releasing the
compressor tool.
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. Valve lifters must
be kept in order so they may be reinstalled in their
original position.
VALVE LIFTER DIAGNOSIS
1. Momentarily noisy when vehicle is started:
This condition is normal. Oil drains from the
lifters which are holding the valves open when
the engine is not running. It will take a few
seconds for the lifter to fill after the engine is
started.
2.
Intermittently noisy on idle only, disappearing
when engine speed is increased:
Intermittent clicking may be an indication of a
pitted check valve ball, or it may be caused by
dirt.
Correction: Replace lifter.
3.
Noisy at slow idle or with hot oil, quiet with
cold oil or as engine speed is increased:
High leak down rate. Replace suspect lifter.
4. Noisy at high vehicle speeds and quiet at low
speeds:
• High oil level - Oil level above the “ FULL”
mark allows crankshaft counterweights to
churn the oil into foam. When foam is pumped
into the lifters, they will become noisy since a
solid column of oil is required for operation.
Correction: Drain oil until proper level is
obtained, refer to SECTION OB.
• Low oil level - Oil level below the operating
range allows the pump to pump air at high
speeds which results in noisy lifters.
Correction: Fill until proper oil level is
obtained.
• Oil pan bent on bottom or pump screen cocked
or loose.
Correction:
Repair or replace parts as
necessary.
5. Noisy at idle becoming louder as engine
speed is increased to 1500 rpm:
This noise is not connected with lifter
malfunction. It becomes most noticeable in the
vehicle at 10 to 15 mph “L” (Low) range, or
30 to 35 mph “ D” (Drive) range and is best
described as a hashy sound. At slow idle, it may
be entirely gone or appear as a light ticking noise
in one or more valves. It is caused by one or
more of the following:
• Badly worn or scuffed valve tip and rocker
arm pad.
• Excessive valve stem to guide clearance.
• Excessive valve seat runout.
• Off square valve spring.
• Excessive valve face runout.