Bearing Clearance

NOTE: In order to determine the correct replacement insert size, measure the bearing clearance accurately. Either of the following two methods may be used: however, method A gives more reliable results and is preferred.

Method A-yields measurements from which the bearing clearance can be computed.

Method B-yields the bearing clearance directly. Method B does not give any indication of bearing or journal runout.

Method A
1. Measure the crankshaft journal diameter with a micrometer in several places.
2. Ensure the measurements are approximately 90 degrees apart.
3. Average the measurements.
4. Measure taper and runout
5. Ensure that the bearing inserts are installed in the correct bore, and torqued to specification.
6. Measure the bearing insert ID with an inside micrometer.
7. Measure using new inserts, if the inserts are being replaced.
8. If the readings are within limits, select a suitable set of inserts.
9. Bearing sets are available in standard and undersize in order to keep clearances within limits.
10. If clearances cannot be brought into specifications with selectively fitting bearings, replace the crankshaft.

Method B
1. Install all the bearing inserts and the crankshaft into the block.
2. Place a piece of gaging plastic across the entire bearing width.

CAUTION: In order to prevent the possibility of cylinder block or crankshaft bearing cap damage, the crankshaft bearing caps are tapped into the cylinder block cavity using a brass, lead, or a leather mallet before the attaching bolts are installed. Do not use attaching bolts to pull the crankshaft bearing caps into the seats. Failure to observe this information may damage a cylinder block or a bearing cap.

3. Seat the bearing cap carefully. Tap the bearing cap lightly with a suitable tool.

CAUTION: Do not rotate the crankshaft.

4. Tighten the bearing cap bolts to specification.
5. Remove the bearing cap.
6. Leave the gaging plastic in place. It does not matter whether the gaging plastic adheres to the journal or to the bearing cap.
7. Measure the flattened gaging plastic at its widest point with the scale printed on the gaging plastic package.
8. Remove all traces of the gaging plastic after measuring.