Mercury 2C5Z-6303-BA Crankshaft Assembly

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Carefully scrape all traces of the Plastigage material off the main bearing journals and bearing insert faces.

Push the crankshaft all the way to the rear and zero the dial indicator. Next, pry the crankshaft to the front as far as possible and check the reading on the dial indicator. The distance that it moves is the endplay. If it's greater than the limit, check the crankshaft thrust surfaces for wear. If no wear is evident, new main bearings should correct the endplay.

Using a micrometer, measure the diameter of the main and connecting rod journals and compare the results to the Chapter's Specifications. Measure the diameter at several points to detect taper and out-of-round conditions. Take measurements at each end of the journal, near the crank throws, to determine if the journal is tapered.

Install the main cap bolts and tighten them to 10-to-12 ft-lbs. The crankshaft main bearing cap bolts must be replaced with new bolts as they are designed as torque-to-yield bolts and cannot be reused once removed.

Rubbing a penny lengthwise on each journal will reveal its condition. If copper rubs off and is embedded in the crankshaft, the journals should be reground. If a journal picks up copper from the penny, it's too rough and must be reground.

Check the main bearing caps to see if they're marked to indicate their locations. They should be numbered consecutively from the front of the engine to the rear. If they aren't, mark them with number stamping dies or a center-punch.

If they're still in place, remove the original bearing inserts from the block and the main bearing caps. Wipe the bearing surfaces of the block and caps with a clean, lint-free cloth. They must be kept spotlessly clean.

Check the crankshaft thrust surfaces for wear after removal. If no wear is evident, new main bearings should correct the endplay.