Pontiac Fiero 1988 Service Manual page 288

GENERAL ENGINE MECHANICAL 6A-11
3.
Looseness or rotation (flattened tangs and
wear grooves)
Thrust surfaces (main thrust bearing) for:
Wear
Grooving. Grooves are caused by
irregularities of the crankshaft thrust
surface. Refer to Crankshaft.
Important
• Bearing failure, other than normal wear,
must be investigated carefully. Inspect the
crankshaft or connecting rod and the
bearing bores.
Bearing cap bolts. If bolts are stretched, replace
them.
Measure
Bearing clearance. To determine the correct
replacement insert size, the bearing clearance
must be measured accurately. Either of the
following two methods may be used, however,
method "A" gives more reliable results and is
preferred.
f | Important
• Method "A" yields measurements from
which the bearing clearance can be
c o m p u t e d .
Method "B" yields the bearing
clearance
d i r e c t l y .
Method "B" does
n o t
give any indication of bearing run-out.
© Do not mix inserts of different nominal size
in the same bearing bore.
m Method "A"
1 Measure the crankshaft journal diameter with a
micrometer in several places, approximately 90°
apart, and average the measurements.
2. Taper and runout. (Refer to basic engine section
for allowable limits.)
3. Bearing insert I.D. with an inside micrometer.
Measure using new inserts if the inserts are being
replaced.
[T"| Important
• The bearing cap must be torqued to
specification when the measurement is
taken.
© If the readings are within limits, select a
suitable set of inserts. If the readings are
unsatisfactory, the crankshaft journal must
be reconditioned and undersized bearing
inserts installed.
• Crankshafts which have rolled fillets cannot
be reground. They must be replaced.
• Method "B"
L Install bearing inserts and crankshaft into block.
2. Place a piece of gaging plastic across the
e n t i r e
bearing width.
3. Seat the bearing cap carefully by tapping it lightly
with a suitable tool.
N O T I C E :
To avoid cylinder block and/or main
bearing cap damage, the main bearing caps are to
be tapped into their cylinder block cavity using a
brass, lead or leather mallet before attaching bolts
are installed. Do not use attaching bolts to pull
main bearing caps into their seats. Failure to
observe this information may damage a cylinder
block or bearing cap.
4. Torque bearing cap bolts to specification.
| "9" J Important
• Do not rotate the crankshaft.
5. Remove the bearing cap, leaving the gaging
plastic in place. It does not matter whether the
gaging plastic adheres to the journal or to the
bearing cap.
6. Measure the flattened gaging plastic at its
w i d e s t p o i n t
with the scale printed on the
gaging plastic package (Figure 26).
G20023-6A
Figure 2 6 Measuring Bearing Clearance
7. Remove all traces of the gaging plastic after
measuring.
8. Select a set of bearing inserts that will produce the
desired clearance.
•»4* Install or Connect
N O T I C E :
Bearing inserts must not be shimmed,
scraped or filed. Do not touch the bearing surface
of the insert with the bare fingers. Skin oil and
acids will etch the bearing surface.
Important
• Make sure the bearing cap bolt holes and
the cap mating surfaces are clean and dry.
(Refer to Rear Main Bearing for rear main
bearing cap sealing procedure.)
1. Dip bearing cap bolts in clean engine oil.
2. Place inserts into the bearing cap and into the
engine block or connecting rod.
N O T I C E :
Upper and lower inserts may be
different. Be careful to align holes. Do not obstruct
any oil passages.