Tools Required

J 7872  Magnetic Base Dial Indicator Set

1. Using a suitable fixture, support the crankshaft.
   Fig 1: Supporting Crankshaft

   Courtesy of GENERAL MOTORS CORP.
2. Install the J 7872 
3. Measure the crankshaft runout using J 7872  Refer to Engine Mechanical Specifications .
   Fig 2: Installing J 7872

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4. Measure the crankshaft thrust wall width (1) for wear using an inside micrometer. Refer to Engine Mechanical Specifications .
5. Measure the crankshaft thrust wall surface (2) for runout using J 7872  Refer to Engine Mechanical Specifications .
6. If the crankshaft journals are damaged or worn beyond specifications, replace the crankshaft. No machining of the crankshaft journals is allowed.
   Fig 3: Measuring Crankshaft Thrust Wall Width

   Courtesy of GENERAL MOTORS CORP.
7. Check the crankpins for undersize using an outside micrometer.
Fig 4: Checking Crankpins
Courtesy of GENERAL MOTORS CORP.
8. Compare your measurements with those listed in the Engine Mechanical Specifications . If the crankshaft journals are worn beyond the specified limits, the crankshaft must be replaced. Crankshaft machining is not allowed and there are no undersized bearings available for service.
9. Measure the main bearing and crankpin journals for out-of-round using the following procedure:
   1. 9.1. Using at outside micrometer, measure the journal at the extreme front and rear location; on the journal. Call these points A and B.
   2. 9.2. Measure the journal in two new locations exactly 90 degrees from the first points. Call these points C and D.
   3. 9.3. Subtract A from C and B from D. The differences will indicate journal out-of-round.
   4. 9.4. The out-of-round should not exceed 0.004 mm (0.00016 in.) maximum.
   5. 9.5. If the specifications are exceeded, replace the crankshaft.
   Fig 5: Measuring Main Bearing & Crankpin Journals

   Courtesy of GENERAL MOTORS CORP.
10. Measure the main bearing and crankpin journals for taper using the following procedure:
    1. 10.1. Using an outside micrometer, measure the journal at the extreme front (A) and area (B) of the journal parallel to the crankshaft centerline.
    2. 10.2. Subtract the smallest from the largest measurement. The result will be the journal taper.
    3. 10.3. If the main bearing journal taper exceeds 0004 mm (0.00016 in), replace the crankshaft.
    4. 10.4. If the crankpin journal taper exceeds 0004 mm (0.00016 in), replace the crankshaft.