Engine Rebuilding: The Crankshaft

In Engine Rebuilding: The Preparation, we discussed various ways to rebuild your engine and how to find a competent machine shop to help you in the process. Part 2 will deal with the first step in putting it all back together—installing the crankshaft in the cylinder block.

Getting Ready
When you get your engine parts back from the machine shop everything should be ready for a final cleaning and assembly. Make sure that you have everything you need before you start the process. That will include the cylinder block, crankshaft, main bearings, rear main seal, torque wrench and Plastigauge. If you are fully equipped with inside and outside micrometers, you can skip the Plastigauge.


The first step is to thoroughly wash the engine block with detergent and water for the last time and blow it dry with compressed air. If you don't have compressed air it can air dry but make certain that you turn it over several times to get the water out of bolt holes, then coat all machined surfaces with a light coat of oil to prevent rust. Give the crankshaft a good scrubbing with detergent and a soft brush and a blow-dry as well. Coat the bearing surfaces with a light coat of oil.

Getting Your Bearings
If your engine is typically on its first rebuild, the engine machine shop probably ground the crankshaft .010-inch undersize to make the bearing journals round and provide a fresh bearing surface. That means that you will need to use .010 oversize (thicker) bearings to restore the correct bearing clearances. Crankshafts are ground up to .030 undersize in increments of .010. Make sure you have the correct size bearings for your crankshaft. If they have been installed in the engine, they are not returnable.


The rear main bearing seal is usually included in the gasket rebuild kit. Sometimes it is not included. Also, several vintage engines use a rope-type rear seal that is prone to leaking. A modern neoprene lip seal is usually available from aftermarket sources that specialize in your marque. So check the car club web sites and forums for availability.