Crankshaft Main Bearing: Service and Repair

MEASURING CRANKSHAFT MAIN BEARING CLEARANCE IN-CAR

PLASTIGAGE METHOD





Engine crankshaft bearing clearances can be determined by use of Plastigage (1) or equivalent. The following is the recommended procedure for the use of Plastigage:

1. Remove oil film from surface to be checked. Plastigage is soluble in oil.
2. The total clearance of the main bearings can only be determined by removing the weight of the crankshaft. This can be accomplished by either of two methods:

PREFERRED METHOD

1. Support the bearings adjacent to the bearing to be checked in order to remove the clearance between upper bearing shell and the crankshaft. This can be accomplished by placing a minimum of 0.254 mm (.010 inch) shim (e. g. cardboard, matchbook cover, etc.) between the bearing shell and the bearing cap on the adjacent bearings and tighten bolts to 14-20 Nm (10-15 ft.lb.)
- When checking No. 1 main bearing. Support No. 2 main bearing.
- When checking No. 2 main bearing. Support No.1 and No. 3 main bearing.
- When checking No.3 main bearing. Support No. 2 and No. 4 main bearing.
- When checking No. 4 main bearing. Support No. 3 and No. 5 main bearing.
- When checking No. 5 main bearing. Support No. 4 and No. 6 main bearing.
- When checking No. 6 main bearing. Support No. 5 main bearing.





2. Remove the bearing cap and compare the width of the flattened Plastigage with the metric scale provided on the package. Locate the band closest to the same width. This band shows the amount of clearance in thousandths of a millimeter. Differences in readings between the ends indicate the amount of taper present. Record all readings taken. Refer to Engine SpecificationsEngine Specifications. Plastigage generally is accompanied by two scales. One scale is in inches, the other is a metric scale.

NOTE: Remove all support before reassembling engine.


ALTERNATIVE METHOD





1. With the weight of the crankshaft being supported by a jack under the counterweight adjacent to the bearing being checked.
2. Place a piece of Plastigage (1) across the entire width of the bearing shell in the cap approximately 6.35 mm (1/4 inch) off center and away from the oil holes. (In addition, suspect areas can be checked by placing the Plastigage in the suspect area). Torque the bearing cap bolts of the bearing being checked to the proper specifications.





3. Remove the bearing cap and compare the width of the flattened Plastigage with the metric scale provided on the package. Locate the band closest to the same width. This band shows the amount of clearance in thousandths of a millimeter. Differences in readings between the ends indicate the amount of taper present. Record all readings taken. Record all readings taken. Refer to Engine SpecificationsEngine Specifications. Plastigage generally is accompanied by two scales. One scale is in inches, the other is a metric scale.
4. Plastigage is available in a variety of clearance ranges. The 0.025-0.076 mm (.001-.003 inch) is usually the most appropriate for checking engine bearing proper specifications.