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6A3-14
1977 PONTIAC SERVICE MANUAL
TANG
\
UNDERSIZE STP
IN THOUSANDS
Fig.
6A3-28
Location of Undersize Mark on Bearing Shel
CRANKSHAFT BEARINGS AND
SEALS
Replacement of Crankshaft Bearings
A crankshaft bearing consists of two halves or shells
which are not alike and not interchangeable in cap and
crankcase. The upper (crankcase) half of the bearing is
grooved to supply oil to the connecting rod bearings while
the lower (bearing cap) half of the shell is not grooved. The
two bearing halves must not be interchanged. All crankshaft
bearings except the thrust bearing and rear main upper are
identical. The thrust bearing (No. 2)is flanged to take end
thrust and the rear main upper bearing groove does not
extend the full arc of the bearing. When the shells are placed
in crankcase and bearing cap, the ends extend slightly beyond
the parting surfaces so that when cap bolts are tightened the
shells will be clamped tightly in place to insure positive
seating and to prevent turning. The ends of shells must
never be filed flush with parting surface of
crankcase or bearing cap.
Crankshaft bearings are the precision type which do not
require reaming to size. Shims are not provided for
adjustment since worn bearings are readily replaced with new
bearings of proper size. Bearings for service replacement are
furnished in standard size and undersizes. Under no
circumstances should crankshaft bearing caps be
filed to adjust for wear in old bearings.
After removal of oil pan, pipe and screen assembly, and
oil pan baflle, perform the following removal, inspection and
installation operations on each crankshaft bearing in turn so
that the crankshaft will be well supported by the other
bearings.
If crankshaft has been removed to check straightness the
following procedure is suggested.
Rest crankshaft on "V-blocks" at (No. 1 and No. 4
bearing journals). Check indicator runout at (No. 2 and No.
3 journals). Total indicator readings at each journal should
not exceed .0015.
While checking runout at each journal note relation of
"high"spot (for maximum eccentricity) on each journal to the
others.
"Highwspot on all journals should come at the same
angular location. If "high"spots do not come at nearly the
same angular location, crankshaft has a "crook"or
"doglegwin it and is unsatisfactory for service.
1. Since any service condition which affects the
crankshaft bearings may also affect the connecting rod
bearings, it is advisable to inspect connecting rod bearings
first. If crankpins are worn to the extent that crankshaft
should be replaced or reground, replacement of crankshaft
bearings only will not be satisfactory. If replacement of
cylinder block or crankshaft is required, always check main
bearing clearance with plastic-type gage to obtain specified
limits.
2. Remove one bearing cap, then clean and inspect lower
bearing shell and the crankshaft journal. If journal surface
is scored or ridged, the crankshaft must be replaced or
reground to insure satisfactory operation with new bearings.
Slight roughness may be polished out with fine grit polishing
cloth thoroughly wetted with engine oil, and burrs may be
honed off with a fine stone.
3. If condition of lower bearing shell and crankshaft
journal is satisfactory, check the bearing clearance with
plastic-type gage as described for the connecting rod bearing.
4. When checking a crankshaft bearing with plastic-type
gage, turn crankshaft so that oil hole is up to avoid dripping
of oil on plastic-type gage. Place paper shims in lower halves
of adjacent bearings and tighten cap bolts to take the weight
of crankshaft off the lower shell of bearing being checked.
Arrow on cap must point to front of engine.
5. If bearing clearance exceeds .003", it is advisable to
install a new bearing; however, if bearing is in good condition
and is not being checked because of bearing noise, it is not
necessary to replace the bearing.
6. Loosen all crankshaft bearing cap bolts 1/2 turn, and
remove cap of bearing to be replaced.
7. Remove upper bearing shell by inserting Bearing Shell
Remover and Installer J 8080 in oil hole in crankshaft, then
slowly turning crankshaft so that the tool rotates the shell out
of place by pushing against the end without the tang. See Fig.
6A3-29.
When turning crankshaft with rear bearing cap removed,
hold oil seal to prevent it from rotating out of position in
crankcase.
8. The crankshaft journal cannot be measured with an
outside micrometer when shaft is in place; however, when
upper bearing shell is removed the journal may be checked
for out-of-round by using a special crankshaft caliper and
inside micrometer. The caliper should not be applied to
journal in line with oil hole.
If crankshaft journal is more than .0015" out-of-round,
the crankshaft should be replaced since the full mileage
cannot be expected from bearings used with an excessively
out-of-round crankshaft.
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