Chevrolet 1980 Light Duty Truck Service Manual page 440

6A 1-22 IN-LINE 6
Fig. 6 A 1 - 3 0 - G a g i n g Plastic on Journal - Typical
be observed. If the engine is out of 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 journal. If the engine is to remain in the vehicle, the
crankshaft must be supported upward to remove any
clearance from the upper bearing. The total clearance can
then be measured between the lower bearing and journal.
To assure the proper seating of the crankshaft all
bearing cap bolts must be at their specified torque. In
addition, preparatory to checking fit of bearings, the surface
of the crankshaft journal and bearing must be wiped clean
Fig. 6 A 1 -3 1 ~ M e a s u rin g Gaging Plastic - Typcial
Fig. 6 A 1 -3 2 --M e a s u r in g Cr an kshaft End Play - Typical
of oil.
1. With the oil pan and oil pump removed, and starting
with the rear main bearing, remove bearing cap and wipe
oil from journal, both bearing shells and bearing cap.
2. Place a piece of gaging plastic the full width of the
bearing (parallel to the crankshaft) on the journal (fig. 6A1-
30).
Do not rotate the crankshaft while the gaging plastic
is between the bearing and journal.
3. Install the bearing cap and evenly torque the
retaining bolts to 65 lb. ft. (88N*m ). Bearing cap MUST
be torqued to specification in order to assure proper reading.
Variations in torque affect the compression of the plastic
gage.
4. Remove bearing cap. The flattened gaging plastic
will be found adhering to either the bearing shell or journal.
5. On the edge of gaging plastic envelope there is a
graduated scale which is correlated in thousandths of an
inch. Without removing the gaging plastic, measure its
compressed width,
a t the w idest point
graduations on the gaging plastic envelope (fig. 6A1-31).
Normally, main bearing journals wear evenly and are
not out-of-round. However, if a bearing is being fitted to an
out-of-round journal (.001" max.), be sure to fit to the
maximum diameter of the journal. If the bearing is fitted
to the minimum diameter and the journal is out-of-round
.001", interference between the bearing and journal will
result in rapid bearing failure. If the flattened gaging plastic
tapers toward the middle or ends, there is a difference in
clearance indicating taper, low spot or other irregularity of
the bearing or journal. Be sure to measure the journal with
a micrometer if the flattened gaging plastic indicates more
than .001" difference.
6. If the bearing clearance is within specifications, the
bearing insert is satisfactory. If the clearance is not within
specifications, replace the insert. Always replace both upper
, with the
LIG H T T R U C K S E R V IC E M AN UAL