Chevrolet 1988 Light Duty Truck Repair Manual page 349

Figure 36 — Reaming the Valve Guides (Typical)
MEASURING MAIN BEARING CLEARANCE
Main bearings are of the precision insert type and do
not use shim s for adjustment. If clearances are found to
be excessive, new upper and lower inserts will be re­
quired.
The sim plest, most accurate way to measure main
bearing clearance is with the use of gaging plastic. This
wax-like m aterial compresses evenly between the bearing
and journal surfaces w ithout dam aging them. Proceed as
follows:
C lean
All oil from the crankshaft journal and main bearing
inserts.
Install or C on n ect (F ig u re 37)
Refer to the proper section for additional inform a­
tion.
Main bearing inserts and crankshaft, as outlined in
the proper section.
Gaging plastic.
• Begin with the rear main bearing.
• W ipe 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