Plastic Gage Method for Crankshaft Bearings

Important:  When bearings are removed, NEW bearings must be installed during reassembly.

1. Install the crankshaft and the new crankshaft bearings into the block, making sure not to damage the reluctor rings of the crankshaft.
   Fig 1: Crankshaft, Bearings, Caps, Bolts & Studs

   Courtesy of GENERAL MOTORS CORP.
2. Install the gaging plastic the full width of the crankshaft journal.
   NOTE: Refer to FASTENER NOTICE in Cautions and Notices.

   Important:  Tighten the inner crankshaft bearing cap bolts before tightening the outer crankshaft bearing cap studs. The crankshaft journal and the crankshaft bearing surface must be free from oil to obtain a correct measurement. Do not allow the crankshaft to rotate while performing the measurement, or an incorrect measurement will be obtained.

3. Install the crankshaft bearing caps and the crankshaft bearing cap bolts and studs.

   Tighten 

   1. 3.1. Tighten the crankshaft bearing cap inner bolts to 30 N.m (22 lb ft).
   2. 3.2. Tighten the crankshaft bearing cap outer studs to 30 N.m (22 lb ft).
   3. 3.3. Using J 36660-A  , tighten the crankshaft bearing cap inner bolts an additional 90 degrees.
   4. 3.4. Using J 36660-A  , tighten the crankshaft bearing cap outer studs an additional 80 degrees.
4. Remove the crankshaft bearing cap bolts and the crankshaft bearing caps. The gaging plastic may adhere to either the crankshaft journal or the crankshaft bearing surfaces.
   Fig 2: Gaging Plastic Installed On Crankshaft Journal

   Courtesy of GENERAL MOTORS CORP.
5. On the edge of the gaging plastic envelope there is a graduated scale. Without removing the gaging plastic, measure the compressed width at the widest point.
6. If the flattened gaging plastic tapers toward the middle or the ends, there may be a difference in clearance indicating taper, low spot or other irregularity of the crankshaft bearing or the crankshaft journal.
   • Normally the crankshaft journals wear evenly and are not out-of-round. However, if a crankshaft bearing is being fitted to an out-of-round 0.0254 mm (0.001 in maximum) crankshaft journal, be sure to fit to the maximum diameter of the crankshaft journal.
   • If the crankshaft bearing is fitted to the minimum diameter and the crankshaft journal is excessively out-of-round, the interference between the crankshaft bearing and the crankshaft journal will result in rapid crankshaft bearing failure.
7. Compare the crankshaft bearing clearance to the specifications. Refer to Engine Mechanical Specifications .
8. If the crankshaft bearing clearances exceeds specifications, replace components as required.
9. Measure the new crankshaft bearing inside diameter (ID) using the same method.
10. Replace the crankshaft if the proper clearances cannot be obtained with standard size bearings.
11. Remove the flattened gaging plastic.
12. Measure the remaining crankshaft journals.
    Fig 3: Measuring Crankshaft Bearing Inside Diameter

    Courtesy of GENERAL MOTORS CORP.