Micrometer Method for Crankshaft Bearings

Important:  When bearings are removed, NEW bearings must be installed during reassembly.

1. Measure the crankshaft main journal diameter with a micrometer in several places along the length approximately 90 degrees apart, minimum of 4 places, and average the measurements.
2. Determine the taper and the out-of-round. Refer to Engine Mechanical Specifications .
   Fig 1: Measuring Crankshaft Main Journal Diameter

   Courtesy of GENERAL MOTORS CORP.
3. Install the NEW crankshaft bearings into the crankshaft bearing caps and the engine block.
   NOTE: Refer to FASTENER NOTICE in Cautions and Notices.

   Important:  Tighten the inner crankshaft bearing cap bolts before tightening the outer crankshaft bearing cap studs.

4. Install the crankshaft bearing caps and the crankshaft bearing cap bolts and studs.

   Tighten 

   1. 4.1. Tighten the crankshaft bearing cap inner bolts to 30 N.m (22 lb ft).
   2. 4.2. Tighten the crankshaft bearing cap outer studs to 30 N.m (22 lb ft).
      Fig 2: Crankshaft Bearing Cap, Bolts & Studs

      Courtesy of GENERAL MOTORS CORP.
   3. 4.3. Using J 36660-A  , tighten the crankshaft bearing cap inner bolts an additional 90 degrees.
   4. 4.4. Using J 36660-A  , tighten the crankshaft bearing cap outer studs an additional 80 degrees.
5. Measure the crankshaft bearing inside diameter (ID) using an inside micrometer. Measure at a minimum of four places and average the measurements.
6. In order to determine the crankshaft bearing clearance, subtract the crankshaft journal diameter from the crankshaft bearing ID.
7. Compare the crankshaft bearing clearance to the specifications. Refer to Engine Mechanical Specifications .
8. If the crankshaft bearing clearances exceeds specifications, install undersize crankshaft bearings to achieve the correct clearance.
9. Measure the new crankshaft bearing inside diameter (ID) using an inside micrometer.
10. Replace the crankshaft if the proper clearances cannot be obtained with standard size bearings.