Measuring Bearing Clearance Using PLASTIGAGE

Fig 1: Plastigage Placed On Crankshaft - Typical

Courtesy of DAIMLERCHRYSLER CORP.

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. Place a piece of Plastigage (1) across the entire width of the bearing shell in the cap approximately 6.35 mm (1/4 in.) off center and away from the oil holes. See Fig 1. (In addition, suspected areas can be checked by placing the Plastigage in the suspected area). Torque the bearing cap/bed plate bolts of the bearing being checked to the proper specifications.
   Fig 2: Connecting Rod Bearing Clearance - Typical

   Courtesy of DAIMLERCHRYSLER CORP.
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. Compare clearance measurements to specs found in engine specifications (Refer to ENGINE - SPECIFICATIONS)  . Plastigage generally is accompanied by two scales. One scale is in inches, the other is a metric scale. 
   NOTE: Plastigage is available in a variety of clearance ranges. Use the most appropriate range for the specifications you are checking.
4. Install the proper crankshaft bearings to achieve the specified bearing clearances.