Crankshaft and Bearings Cleaning and Inspection: Notes

Tools Required 

• J 8087  Cylinder Bore Gage
• J 36660-A  Torque Angle Meter

Fig 1: Crankshaft
Courtesy of GENERAL MOTORS CORP.
1. Clean the crankshaft of the following elements:
   • Oil
   • Sludge
   • Carbon
2. Inspect the crankshaft oil passages for obstructions.
Fig 2: Crankshaft Key Components
Courtesy of GENERAL MOTORS CORP.
3. Inspect the crankshaft keyway for the following conditions:
   • A worn crankshaft key (1)
   • A worn crankshaft keyway (2)
4. Inspect the crankshaft threads (3) for damage.

   Important  : If cracks, severe gouges or burned spots are found, replace the crankshaft. Remove slight roughness using a fine polishing cloth soaked in clean engine oil. Remove any burrs using a fine oil stone.

Fig 3: Crankshaft Components
Courtesy of GENERAL MOTORS CORP.
5. Inspect the crankshaft bearing journals and the crankshaft thrust surfaces for the following conditions:
   • Wear without any grooves or scratches (1)
   • Grooves or scoring (2)
   • Scratches or excessive wear (3)
   • Pitting or embedded bearing material (4)

     Inspect the corresponding crankshaft bearing inserts for embedded material and determine the source of the material.

   • Overheating (discoloration)
Fig 4: Crankshaft Bearings
Courtesy of GENERAL MOTORS CORP.
6. The crankshaft bearings are the precision insert type.
7. Inspect the outer surfaces of the crankshaft bearings for the following conditions:
   • Wear - surface wear indicates either movement of the insert, or high spots in the surrounding material (spot wear).
   • Overheating or discoloration
   • Looseness or rotation indicated by flattened tangs and wear grooves

   Important  : Note the location of the crankshaft main bearing high spots. If the spots are not in line, the crankshaft is bent. Replace the crankshaft.

Fig 5: Identifying Crankshaft Defects
Courtesy of GENERAL MOTORS CORP.
8. Inspect the crankshaft main bearings for craters or pockets. Flattened sections on the crankshaft bearing halves also indicate fatigue.
9. Inspect the thrust surfaces of the main thrust bearing for the following conditions:
   • Wear
   • Grooving - Grooves are caused by irregularities of the crankshaft thrust surface.
10. Inspect the crankshaft bearings for excessive scoring or discoloration.
11. Inspect the crankshaft main bearings for dirt or imbedded debris.
    Fig 6: Identifying Crankshaft Faults

    Courtesy of GENERAL MOTORS CORP.
12. Inspect the crankshaft main bearings for improper seating indicated by bright, polished sections.
13. Inspect the crankshaft bearings for uneven side-to-side wear. This may indicate a bent crankshaft or a tapered bearing journal.
    Fig 7: Identifying Crankshaft Faults

    Courtesy of GENERAL MOTORS CORP.

    Important  : If crankshaft bearing failure is due to conditions other than normal wear, investigate the cause of the condition. Inspect the crankshaft or connecting rod bearing bores.

Fig 8: Measuring Bearing Bore
Courtesy of GENERAL MOTORS CORP.
14. Inspect the connecting rod bearing bores or crankshaft main bearing bores using the following procedure:
    1. Tighten the bearing cap to specification.
    2. Use the J 8087  in order to measure the bearing bore for taper and out-of-round. Record the readings for bearing selection.
    3. No taper or out-of-round should exist.