Chevrolet 1977 light duty truck, Service Manual

Page: 511 / 861

Fig. 6A-58V--M easuring C onnecting Rod Side
Clearance
inserts is necessary in production in o rder to obtain close
tolerances. F o r this reason you m a y find one h a lf o f a
sta n d a rd insert with one h a lf o f a .001" undersize insert
which will decrease the clearance .0005" from using a
full sta n d a rd bearing.
W h e n a production cra n k sh a ft cannot be precision
fitted by this method, it is then ground .009" undersize
on main journals only. A .0 0 9 " undersize bearing and
.0 1 0 " undersize bearing may be used for precision
fitting in th e sa m e m a n n e r as previously described. Any
e n g in e fitted with a .0 0 9 " undersize c ra n k s h a ft will be
identified by t h e following m arkings.
• ".009" will be stam ped on the crankshaft
counterw eight forward o f the center m ain jo urnal.
• A figure " 9 " will be stam ped on the block at
the left front oil p a n rail.
N O T E : If, for any reason, m ain bearing caps are
replaced, shim m ing m ay be necessary. L am inated
shims for each cap are available for service. Shim
r e q u i r e m e n t will
be d e te r m in e d by b e a rin g
clearance.
Inspection
In general, the lower h a lf o f the bearing (except No.
1 bearing) shows a greater w ear and the most distress
from fatigue. If upon inspection the lower half is
suitable for use, it can be assum ed that the upper h a lf is
also satisfactory. If the lower h a l f shows evidence o f
w ear o r d am age, both u pper and lower halves should be
replaced. N ev er replace one h a lf without replacing the
other half.
C hecking C learance
To obtain the most accurate results with "Plasti-
gage", (or its equivalent) a wax-like plastic m aterial
which will compress evenly between the bearing and
jo u rn a l surfaces without d am a g in g either surface, certain
precautions should be observed.
If the engine is out o f the vehicle and upside down,
the crankshaft will rest on the upper bearings and the
total clearance can be measured between the lower
bearing and jou rn al. If the engine is to rem ain in the
vehicle, the c ra n k sh a ft should be supported both front
and re a r (d a m p e r and flywheel) to remove the clearance
from the u pper bearing. The total clearance can then be
measured between the lower bearing and journal.
NOTE: To assure the p ro p er seating o f the
crankshaft, all bearing cap bolts should be at their
specified
torque. In addition, p re p a ra to ry to
checking fit o f bearings, the surface o f the
crankshaft jo u r n a l and bearing should be wiped
clean o f oil.
1. With the oil p a n and oil p u m p removed, and
starting with the re a r m ain bearing, remove bearing cap
and wipe oil from jo u rn a l and bearing cap.
2. Place a piece o f gauging plastic the full width o f
the bearing (parallel to the crankshaft) on the journal
(fig. 6A-59V).
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. T he flattened gauging
plastic will be found ad h erin g to either the bearing shell
or journal.