GM 10224877 Engine Crankshaft

The crankshaft and main bearings ought not to be removed except when the engine has been removed from the car, and the engine should initially be dismantled. It is advisable that each of the five main bearing caps should be labeled to show where they belong in the engine block; if this is done, indentations as would be done with the connecting rods and caps should be made. After loosening the main bearing caps they should each be removed from the crankshaft with their corresponding bearing and should be laid on another work bench numbered as per the position of the bearing caps on the engine. The crankshaft can then be slowly pulled out with the use of lifters so as not to wreck the engine block. The two halve of the rear main bearing oil seal has to be detached, The crank shaft main bearings together with the cylinder block and main bearing caps should be withdrawn in such a manner that they will not be mixed since they have their own positions. Last, the crankshaft gear at the front must be removed which is best to be done with a puller intended for this job.

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.

Finally, lift the crankshaft out of the engine, ideally with assistance, and return the bearing inserts to their positions in the block and main bearing caps, tightening the bolts finger tight.

Finally, examine the main and rod bearing inserts.

Using a micrometer, measure the diameter of the main and connecting rod journals at several points to detect taper and out-of-round conditions, taking measurements at each end of the journal near the crank throws.

To check the endplay of the crankshaft, mount a dial indicator with the stem in-line with the crankshaft and touching one of the crank throws. The crankshaft should be pushed all the way to the rear, and the dial indicator should be zeroed. Then, the crankshaft should be pried to the front as far as possible, and the reading on the dial indicator should be checked. The distance it moves is the endplay.

Push the crankshaft as far forward as possible and use a feeler gauge to measure the gap between the front of the rear main bearing and the crankshaft thrust surface.

Apply a thin, even layer of clean moly-base grease or engine assembly lube to the bearing surfaces in the block.

Examine the main and rod bearing inserts for further assessment.

After removing the bolts and caps, compare the width of the crushed Plastigage to determine the oil clearance, ensuring it meets specifications.

Before removing the crankshaft, check the endplay by mounting a dial indicator with the stem aligned with the crankshaft and touching one of the crank throws.