Measuring Main Bearing C Le A Ra N C - GMC 1989 Light Duty Truck Repair Manual

Figure 36— Reaming the Valve Guides (Typical)
MEASURING MAIN BEARING CLEARANCE
Main bearings are of the precision insert type and do
not use shims for adjustment. If clearances are found to
be excessive, new upper and lower inserts will be re­
quired.
The simplest, most accurate way to measure main
bearing clearance is with the use of gaging plastic. This
wax-like material compresses evenly between the bearing
and journal surfaces without dam aging them. Proceed as
follows:
)Q I Clean
• All oil from the crankshaft journal and main bearing
inserts.
0 ♦ 1 1 Install or C onnect (Figure 37)
• Refer to the proper section for additional informa­
tion.
1. Main bearing inserts and crankshaft, as outlined in
the proper section.
2. Gaging plastic.
• Begin with the rear main bearing.
• Wipe the oil from the crankshaft journal and
the lower main bearing insert.
GENERAL ENGINE MECHANICAL 6A-19
Figure 37— Placing the Gaging Plastic on the
• Place a piece of gaging plastic the full width of
the lower bearing insert (parallel to the crank­
shaft) on the journal (figure 37). Do not rotate
Bearing Journal