Chevrolet 1977 light duty truck, Service Manual

Page: 472 / 861

c ra n k sh a ft jo u rn a l and bearing should be wiped
clean o f oil.
1. W ith the oil pan an d oil p u m p removed, and
staring with the re a r m ain bearing, remove bearing cap
and wipe oil from jo u r n a l and bearing cap.
2. Place a piece o f g auging plastic the full w idth o f
the b earin g (parallel to the crankshaft) on the jo u rn al
(fig. 6A-51).
CAUTION: Do not rotate the crankshaft while
the gauging plastic is between the bearing and
journal.
3. Install the bearing cap and evenly torque the
retaining bolts to specifications.
4. Remove b earin g cap. The flattened gauging
plastic will be fo und a d h e rin g to either the bearing shell
or jou rn al.
5. On the edge o f gauging plastic envelope there is
a grad u ated scale which is correlated in thousandths o f
an inch. W ithout rem oving the gauging plastic, measure
its compressed w id th (at the widest point) with the
g rad u atio n s on the g auging plastic envelope (fig. 6A-52).
N O T E : N ormally, m ain bearing journals w ear
evenly and are not out-of-round. However, if a
b earin g is being fitted to an out-of-round jo u rn a l
(.001" max.), be sure to fit to the m axim um
d ia m e te r o f the journal.
If the b earin g is fitted to the m in im u m d iam eter
and the jo u rn a l is out-of-round .001", interference
between the bearing and jo u rn a l will result in
rapid bearing failure. If the flattened gauging
plastic tapers toward the middle or ends, there is a
difference in clearance indicating taper, low spot or
o ther irregularity o f the bearing or jou rn al. Be sure
to m easure the jo u rn a l with a m icrom eter if the
flattened gauging plastic indicates m ore than .001"
difference.
6. If the b earin g clearance is within specifications,
the b earin g insert is satisfactory. If the clearance is not
within specifications, replace the insert. Always replace
b oth upp er and lower insert as a unit.
N O T E : If a new b earin g cap is being installed and
clearance is less tha .001", inspect for burrs or
nicks; if none are found then install shim s as
required.
7. A standard, .001" or .002" undersize bearing
may produce the p ro p er clearance. If not, it will be
necessary to regrind the cra n k sh a ft jo u rn a l for use with
the next undersize bearing.
8. Proceed to the next bearing. A fter all bearings
have been checked, rotate the c ra n k sh a ft to see that
there is no excessive drag.
9. M easure crankshaft end play (see specifications)
by forcing the crankshaft to the extreme front position.
M easure at the fro n t end o f the re a r m ain bearing with
a feeler gauge (fig. 6A-53).
10. Install a new rear main bearing oil seal in the
cylinder block and m ain bearing cap.
Replacement
N O TE: M ain bearings may be replaced with or
without rem oving the crankshaft.
W ith C rankshaft Removed
1. Remove and inspect the crankshaft.
2. Remove the m ain bearings from the cylinder
block and main bearing caps.
3. Coat bearing surfaces of new, correct size, main
bearings with oil and install in the cylinder block and
m ain bearing caps.
4. Install the crankshaft.
W ithout C ran ksh aft Removal
1. With oil pan, oil p u m p and spark plugs
removed, remove cap on m ain bearing requiring
replacem ent and remove bearing from cap.
2. The rear m ain journal has no oil hole. Replace
the rear main bearing upper half as follows:
a. Use a small drift punch and h a m m e r to start
the upper bearing h a lf rotating out o f block.
b. Use a pair o f pliers (with taped jaws) to hold
the bearing thrust surface to the oil slinger and rotate
the crankshaft to remove bearing (fig. 6A-54).
c. Oil new selected size upper bearing and insert
plain (unnotched) end between crankshaft and indented
or notched side o f block.
d. Use pliers as in rem oving to rotate bearing
into place. The last 1/4 movem ent may be done by
holding just the slinger with the pliers or tap in place
with a drift punch.