Tools Required

J 7872  Magnetic Base Dial Indicator

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: Identifying J 7872

   Courtesy of GENERAL MOTORS CORP.
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 thrust walls are damaged or worn beyond specifications, replace the crankshaft. No machining of the crankshaft thrust wall is allowed.
   Fig 3: Measuring Crankshaft Thrust Wall Surface

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7. Check the crankshaft main journals for undersize using an outside micrometer.
   Fig 4: Checking Crankshaft Main Journals For Undersize

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8. Check the crankpins for undersize using an outside micrometer.
9. 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.
   Fig 5: Checking Crankpins For Undersizing

   Courtesy of GENERAL MOTORS CORP.
10. Measure the main bearing and crankpin journals for out-of-round using the following procedure:
    1. 10.1. Using an outside micrometer, measure the journal at the extreme front and rear locations on the journal. Call these points A and B.
    2. 10.2. Measure the journal in two new locations exactly 90 degrees from the first points. Call these points C and D.
    3. 10.3. Subtract A from C and B from D. The differences will indicate journal out-of-round.
    4. 10.4. The out-of-round should not exceed 0.004 mm (0.00016 in.) maximum.
    5. 10.5. If the specifications are exceeded, replace the crankshaft.
    Fig 6: Measuring Main Bearing & Crankpin Journals

    Courtesy of GENERAL MOTORS CORP.
11. Measure the main bearing and crankpin journals for taper using the following procedure:
    1. 11.1. Using an outside micrometer, measure the journal at the extreme front (A) and rear (B) of the journal parallel to the crankshaft centerline.
    2. 11.2. Subtract the smallest from the largest measurement. The result will be the journal taper.
    3. 11.3. If the main bearing journal taper exceeds 0.004 mm (0.00016 in), replace the crankshaft.
    4. 11.4. If the crankpin journal taper exceeds 0.004 mm (0.00016 in), replace the crankshaft.