Crankshaft Measurement

Special Tools 

J 7872  Magnetic Base Dial Indicator

For equivalent regional tools, refer to Special Tools .

Fig 1: Proper Support of Crankshaft
Courtesy of GENERAL MOTORS COMPANY
1. Using a suitable fixture, support the crankshaft.
Fig 2: View of J 7872 Measuring Crankshaft Runout
Courtesy of GENERAL MOTORS COMPANY
2. Install the J 7872  indicator.
3. Measure the crankshaft runout using J 7872  indicator. Refer to Engine Mechanical Specifications (LD8) , Engine Mechanical Specifications (L37) .
Fig 3: Expanded View of Crankshaft Thrust Wall Width
Courtesy of GENERAL MOTORS COMPANY
4. Measure the crankshaft thrust wall width (1) for wear using an inside micrometer. Refer to Engine Mechanical Specifications (LD8) , Engine Mechanical Specifications (L37) .
5. Measure the crankshaft thrust wall surface (2) for runout using J 7872  indicator. Refer to Engine Mechanical Specifications (LD8) , Engine Mechanical Specifications (L37) .
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 4: Checking Size of Crankshaft Main Journals
Courtesy of GENERAL MOTORS COMPANY
7. Check the crankshaft main journals for undersize using an outside micrometer.
Fig 5: Checking Crankpins
Courtesy of GENERAL MOTORS COMPANY
8. Check the crankpins for undersize using an outside micrometer.
9. Compare your measurements with those listed in the Engine Mechanical Specifications (LD8) , Engine Mechanical Specifications (L37) . 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 6: Identifying Out-Of-Round Measurements
Courtesy of GENERAL MOTORS COMPANY
10. Measure the main bearing and crankpin journals for out-of-round using the following procedure:
    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. Measure the journal in two new locations exactly 90 degrees from the first points. Call these points C and D.
    3. Subtract A from C and B from D. The differences will indicate journal out-of-round.
    4. The out-of-round should not exceed 0.005 mm (0.00020 in) maximum.
    5. If the specifications are exceeded, replace the crankshaft.
11. Measure the main bearing and crankpin journals for taper using the following procedure:
    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. Subtract the smallest from the largest measurement. The result will be the journal taper.
    3. If the main bearing journal taper exceeds 0.008 mm (0.00032 in), replace the crankshaft.
    4. If the crankpin journal taper exceeds 0.008 mm (0.00032 in), replace the crankshaft.