Crankshaft Main Bearing Selection

Tools Required 

J 36660-A  Torque Angle Meter

1. The crankshaft bearings are of the precision insert type. The crankshaft bearings are available in standard and various undersizes.

   Important:  If crankshaft bearing failure is due to other than normal wear, investigate the cause. Inspect the crankshaft bearing bores.

2. Inspect the crankshaft main bearing bores using the following procedure:
   1. 2.1 Tighten the bearing cap to specification.
   2. 2.2 Measure the bearing bore for taper and out-of-round.
   3. 2.3 No taper or out-of-round should exist.
   Fig 1: Inspecting Crankshaft And Bearing

   Courtesy of GENERAL MOTORS CORP.
3. Install the original crankshaft main bearing inserts on to the cylinder block and the lower crankcase assembly.
4. Carefully place the crankshaft on to the bearing inserts in the cylinder block.
5. Lay a piece of gaging plastic across each crankshaft main journal.

   Important:  Do not turn the crankshaft while measuring the bearing clearance.

6. Carefully place the lower crankcase assembly on to the cylinder block.
   Fig 2: Placing Crankshaft Assembly On To Cylinder Block

   Courtesy of GENERAL MOTORS CORP.
   NOTE: Refer to FASTENER NOTICE .
7. Install the ten main bearing cap bolts.

   Tighten 

   Tighten the crankshaft main bearing cap bolts in the sequence shown, use three progressive steps to obtain 44 N.m (32 lb ft), then use a J 36660-A  and tighten the main bearing cap bolts an additional 90 degrees.

8. After reaching the proper torque, remove the ten crankshaft main bearing cap bolts.
9. Carefully remove the lower crankcase assembly from the cylinder block.
   Fig 3: Identifying Crankshaft Main Bearing Cap Bolts Tightening Sequence

   Courtesy of GENERAL MOTORS CORP.
10. Measure the gaging plastic at its widest point.
    • Standard Oil Clearance: 

      0.016-0.032 mm (0.0006-0.0013 in)

    • Maximum Oil Clearance: 

      0.080 mm (0.0031 in)

      Fig 4: Measuring Gaging Plastic

      Courtesy of GENERAL MOTORS CORP.
11. If using a standard bearing, replace it with one having the same number. If the number of the bearing cannot be determined, select the correct bearing by determining the numbers imprinted on the cylinder block (1-5).
    Fig 5: Identifying Numbers Imprinted On Cylinder Block

    Courtesy of GENERAL MOTORS CORP.
12. If using a standard bearing, replace it with one having the same number. If the number of the bearing cannot be determined, select the correct bearing by determining the numbers imprinted on the crankshaft (1-5). Refer to the Main Bearing Selection Table in ENGINE MECHANICAL SPECIFICATIONS  .
    Fig 6: Determining Numbers Imprinted On Crankshaft

    Courtesy of GENERAL MOTORS CORP.