Measuring Main Bearing Clearance - Gaging Plastic Method

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Fig 1: View Of Gaging Plastic Installed On Crankshaft Journal

Courtesy of GENERAL MOTORS COMPANY

NOTE:

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 affect crankshaft position sensor signals and may affect on-board diagnostics (OBD) II system operation.
Remove the bearing cap side bolts prior to cap removal.

Remove the bearing caps, bearing half, and bolts. Refer to Crankshaft and Bearing Removal .
Install gaging plastic onto the crankshaft journal. Install the gaging plastic the full width of the crankshaft bearing journal.
Install the bearing caps, bearing half, and bolts. Refer to Crankshaft and Bearing Installation .
Remove the bearing caps, bearing half, and bolts. Refer to Crankshaft and Bearing Removal .

Fig 2: Measuring Gaging Plastic

Courtesy of GENERAL MOTORS COMPANY

Using the scale supplied with the plastic gaging kit, measure the gaging plastic at its widest area.
- 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 clearance cannot be brought to specifications, replace the crankshaft or engine block as required. Refer to Engine Mechanical Specifications (L99)Engine Mechanical Specifications (LS3)Engine Mechanical Specifications (LS7) .