Examine the crank pin and main journal surfaces for scoring, scratches, or corrosion; if any are evident, the crankshaft will need professional regrinding. Measure each journal and crank pin at several different points for ovality using a micrometer; if the ovality exceeds 0.001 inch, regrinding is necessary, and undersized bearings are available, though typically the correct matching bearings will be supplied with a reconditioned crankshaft from a GM dealer. After high mileage, main bearings and connecting
Rod Bearings may wear, leading to excessive running clearance, which should be checked using a product like 'Plastigage' after refitting the original bearings and caps and tightening the cap bolts to the specified torque settings. Never attempt to correct excessive running clearance by filing the caps; instead, fit new shell bearings after checking the crankshaft journals and crank pins for ovality and confirming their diameters are standard or regrind sizes. Checking the connecting rod bearings follows a similar process, with the correct running clearance provided in the specifications. It is advisable to check the running clearance of rod and main bearings even when new bearings are installed. The crankshaft end play should be assessed by pushing the crankshaft to the extreme front position and using a feeler gauge at the front end of the rear main bearing to determine permissible clearance. Measure the connecting rod side-clearance with a feeler gauge between the connecting rod caps, and if the side clearance is outside the specified tolerance, replace the rod assembly.