GMC Powertrain 4.3 L, Service Manual, Page: 90 / 196

6-80 Marine/Industrial 4.3L Engine
2000 Marine/Industrial
188015
334338
Bearing Clearance Measuring Procedures
The crankshaft bearings are of the precision insert type and do not
use shims for adjustment. If the clearances are excessive, then
new upper and lower crankshaft bearings will be required. The
service crankshaft bearings are available in the standard size and
an undersize.
The selective fitting of the crankshaft bearings are necessary in
production in order to obtain close tolerances. For this reason, in
one journal bore you may use one-half of a standard crankshaft
bearing with one-half of an undersize crankshaft bearing.
Important: Do not use the plastic gauge method to measure
connecting rod bearing clearances. The plastic gauge method for
measuring connecting rod bearing clearances will result in
unreliable measurements. Use only the micrometer method to
correctly determine the connecting rod bearing clearances.
In order to determine the correct replacement crankshaft bearing
size, the crankshaft bearing clearance must be measured
accurately. Either the micrometer or plastic gauge method may be
used; however, the micrometer method gives more reliable results
and is preferred.
Micrometer Method for Crankshaft Bearings
1. Measure the crankshaft journal diameter with a micrometer
in several places, approximately 90 degrees apart, and then
average the measurements.
2. Determine the taper and the out-of-round of the crankshaft
journal. Refer to Engine Mechanical Specifications.
3. Install the crankshaft bearings into the engine block.