Bearing Selection

WARNING: This page is about a different variant/trim than selected.

Measure the bearing clearance to determine the correct replacement bearing insert size. There are two methods to measure bearing clearance. Method A gives more reliable results and is preferred.
- Method A yields measurement from which the bearing clearance can be computed.
- Method B yields the bearing clearance directly. Method B does not give any indication of bearing run-out.
To measure bearing clearance for the crankshaft (1) using Method A, use the following procedure:

Fig 1: Measuring Bearing Clearance Using Method A
Courtesy of GENERAL MOTORS COMPANY

NOTE: Do not mix inserts of different nominal size in the same bearing bore.
1. Measure the crankshaft bearing journal diameter with a micrometer in several places, 90 degrees apart. Average the measurements.
2. Measure the crankshaft bearing journal taper and runout.
3. Install the lower crankcase and tighten the bearing cap bolts to specification.
4. Measure bearing inside diameter (ID) in several places 90 degrees apart, average measurements.
5. Subtract journal measurement from bearing ID measurement to determine clearance.
6. Determine whether clearance is within specification.
7. If out of specification, choose different inserts.
8. Measure the connecting rod inside diameter in the same direction as the length of the rod with an inside micrometer.
9. Measure the crankshaft main bearing inside diameter with an inside micrometer.
To measure bearing clearance using Method B, use the following procedure:

Fig 2: Measuring Bearing Clearance Using Method B
Courtesy of GENERAL MOTORS COMPANY
1. Clean the used bearing inserts.
2. Install the used bearing inserts.
3. Place a piece of gaging plastic across the entire bearing width at 90 degrees to block/lower crankcase split line.
4. Install the bearing caps.
5. Install the bearing cap bolts to specification.
  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 use this process may damage a cylinder block or a bearing cap.
6. Remove the bearing cap, leaving the gauging plastic in place. It does not matter whether the gauging plastic adheres to the journal or to the bearing cap.
  NOTE: Do not rotate the crankshaft.
7. Measure the gauging plastic at its widest point with the scale (1) printed on the gauging plastic package.
8. Remove the gauging plastic.