Pontiac Fiero 1988 Service Manual page 295

6A-18 GENERAL ENGINE MECHANICAL
ENGINE VALVE ENGINE VALVE
CLOSED OPEN
1 - PUSH ROD
2— PLUNGER
3— LIFTER BODY
4 - CHECK BALL SPRING
5— PLUNGER RETURN SPRING
6— ROLLER
7 - CHECK BALL (OPEN)
8 - CHECK BALL (CLOSED)
G20038-6A
Figure 42 Valve Lifter Operation (Roller Shown)
seconds for the lifter to fill after the engine is
started.
2. I n t e r m i t t e n t l y noisy o n idle only, disappearing
when engine speed is increased:
I n t e r m i t t e n t clicking may be an indication o f a
pitted check valve ball, or i t may be caused by
d i r t .
Correction: Clean the lifter and inspect. I f check
valve ball is defective, replace lifter.
3. Noisy at slow idle, or w i t h hot o i l . Quiet w i t h cold
o i l , or as engine speed is increased:
H i g h leak d o w n rate. Replace suspect lifter.
4. Noisy at h i g h car speeds and quiet at l o w speeds:
a. H i g h o i l level - O i l level above the " F u l l "
m a r k allows crankshaft counterweights to
c h u r n the o i l i n t o foam. W h e n foam is
pumped i n t o the lifters, they w i l l become
noisy, since a solid c o l u m n o f o i l is required
for proper operation.
Correction: D r a i n o i l u n t i l proper level is
obtained. See Section OA.
b. L o w o i l level - O i l level below the "Add"
m a r k allows the p u m p to p u m p air at h i g h
speeds, w h i c h results i n noisy lifters.
Correction: F i l l u n t i l proper o i l level
is
obtained. See Section OA.
c. O i l pan bent on b o t t o m , or p u m p screen
cocked or loose, replace o r repair as
necessary.
5. Noisy at idle becoming louder as engine speed is
increased t o 1500 r p m :
This noise is not connected w i t h lifter
malfunction. I t becomes most noticeable i n the
car at 10 to 15 m p h " L " ( L o w ) range, or 30 to 35
m p h " D " (Drive) range and is best described as
a hashy sound. A t slow idle, i t may be entirely
gone, or appear as a light t i c k i n g noise i n one or
more valves. I t is caused by one or more o f the
following:
a. Badly w o r n or scuffed valve t i p and rocker
a r m pad.
b. Excessive valve stem to guide clearance.
c. Excessive valve seat runout.
d. O f f square valve spring.
e. Excessive valve face runout.
f. Valve spring damper clicking o n rotator.
T o check valve spring and guide clearance,
remove the valve covers.
a. Occasionally this noise can be eliminated by
rotating the valve spring and valve. C r a n k
engine u n t i l noisy valve is off its seat. Rotate
spring. This w i l l also rotate valve. Repeat
u n t i l valve becomes quiet. I f correction is
obtained, check for an off square valve
spring. I f spring is off square more t h a n
1/16" i n free position, replace spring.
(Figure 7).
b. Check for excessive valve stem to guide
clearance. I f necessary, correct as required.
6. Valves noisy regardless o f engine speed:
This condition can be caused by foreign particles,
or excessive valve lash.
Check for valve lash by t u r n i n g engine so the
piston i n that cylinder is o n top dead center o f
firing stroke. I f valve lash is present, the push r o d
can be freely moved up and d o w n a certain
amount w i t h rocker a r m held against valve. I f
O K , clean suspected valve lifters.
Valve Lash
Valve lash indicates one o f the f o l l o w i n g :
a. W o r n push r o d .
b. W o r n rocker a r m .
c. L i f t e r plunger stuck i n d o w n position, due
to d i r t or carbon.
d. F a u l t y lifter.
Checking o f the previous four items:
1. L o o k at the upper end o f push r o d . Excessive
wear o f the spherical surface indicates one o f the
f o l l o w i n g conditions.
a. I m p r o p e r hardness o f the push r o d ball. The
push r o d and rocker a r m must be replaced.
b. I m p r o p e r lubrication o f the push r o d . The
push r o d and rocker a r m must be replaced.
The oiling system to the push r o d should be
checked.
2. I f push r o d appears i n good condition and has
been properly lubricated, replace rocker a r m and
recheck valve lash.
3. I f valve lash exists and push r o d and rocker a r m
are ok, trouble is i n the lifter. L i f t e r should be
replaced.