Measuring Main Bearing Clearance

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IMPORTANT: The crankshaft main bearings are a precision insert type. Main bearing caps are machined with the engine block for proper clearance and cannot be shimmed or filed for bearing fit. If the clearances are found to be excessive, new bearings and/or engine block and cap repair or replacement may be required.

Do not rotate the crankshaft while gaging plastic is between the crankshaft journal and the bearing surface.

The crankshaft bearing clearances are critical. Excessive bearing clearance may effect crankshaft position sensor signals and may effect On-Board Diagnostics (OBD) II system operation.

IMPORTANT: Remove the bearing cap side bolts prior to cap removal.

Remove the bearing cap M8 side bolts.

Fig 1: Bearing Cap M8 Side Bolt
Courtesy of GENERAL MOTORS CORP.
Remove the bearing cap M10 bolts and studs.

Fig 2: Bearing Cap M10 Bolts & Studs
Courtesy of GENERAL MOTORS CORP.

NOTE: Refer to FASTENER NOTICE in Cautions and Notices.
Install the J 41818 to the bearing cap.
Tighten

Tighten the J 41818 bolts to 11 N.m (100 lb in).
Install the J 6125-1B to the J 41818 in order to remove the bearing cap.

Fig 3: Removing Bearing Cap Using J 41818 & J 6125-1B
Courtesy of GENERAL MOTORS CORP.
Remove the bearing cap and lower bearing.

Fig 4: Bearing Cap & Lower Bearings
Courtesy of GENERAL MOTORS CORP.
Install gaging plastic onto the crankshaft journal. Install the gaging plastic the full width of crankshaft bearing journal.

Fig 5: Gaging Plastic Installed Onto Crankshaft Journal
Courtesy of GENERAL MOTORS CORP.
Install the bearing, bearing cap, bolts and bolt/studs.
Tighten
1. 7.1. Tighten the inner bolts (1-10) a first pass in sequence to 20 N.m (15 lb ft).
2. 7.2. Tighten the inner bolts (1-10) a final pass in sequence to 80 degrees using the J 36660-A.
3. 7.3. Tighten the outer bolt/studs (11-20) a first pass in sequence to 20 N.m (15 lb ft).
4. 7.4. Tighten the outer bolt/studs (11-20) a final pass in sequence to 53 degrees using the J 36660-A.
5. 7.5. Tighten the side cap bolts to 25 N.m (18lb ft).
  Tighten the bolt on one side of the bearing cap and then tighten the bolt on the opposite side of the same bearing cap.
Fig 6: Bearing Cap Bolts Tightening Sequence
Courtesy of GENERAL MOTORS CORP.

IMPORTANT: Remove the bearing cap side bolts prior to cap removal.
Remove the bearing cap M8 side bolts.

Fig 7: Bearing Cap M8 Side Bolts
Courtesy of GENERAL MOTORS CORP.
Remove the bearing cap bolts and bolt/studs.

Fig 8: Bearing Cap, Bolts & Studs
Courtesy of GENERAL MOTORS CORP.
Use the J 41818 and the J 6125-1B in order to remove the bearing cap.

Fig 9: Removing Bearing Cap Using J 41818 & J 6125-1B
Courtesy of GENERAL MOTORS CORP.
Measure the gaging plastic at its widest area using the scale supplied with the plastic gaging kit.
- If the gaging plastic shows irregularity in the journal exceeding 0.025 mm (0.001 in), remove the crankshaft and measure the journal with a micrometer.
- If the bearing clearance is greater than 0.052 mm (0.0021 in), select and install an undersized bearing set, and measure the clearance with gaging plastic.
- If clearance cannot be brought to specifications, replace the crankshaft or grind the crankshaft for use with the next undersized bearing.
Fig 10: Measuring Gaging Plastic At Widest Area Using Scale Supplied With Plastic Gaging Kit
Courtesy of GENERAL MOTORS CORP.
Measure the crankshaft end play.
1. 12.1. Thrust the crankshaft forward or rearward.
2. 12.2. Insert a feeler gage between the center crankshaft bearing and the bearing surface of the crankshaft and measure the bearing clearance.
  The proper crankshaft end play clearance is 0.04-0.2 mm (0.0015-0.0078 in).
3. 12.3. If the bearing clearance is not within specifications:
  - Inspect the thrust surfaces for nicks, gouges or raised metal. Minor imperfections may be removed with a fine stone.
  - Replace the thrust bearings and measure the end play.
  - If the correct measurements cannot be obtained, repair the crankshaft thrust surfaces or replace the crankshaft.
  Fig 11: Measuring Crankshaft End Play
  Courtesy of GENERAL MOTORS CORP.