Crank bearings come in several sizes to fit standard cranks and cranks that have been turned. The crankshaft journal may become scored over time. Instead of purchasing a new crankshaft, you can have it turned. When you have the crank turned, it removes a few thousandths of an inch of the material, which would make a standard bearing loose. If the bearings are too loose, the engine will not have enough oil pressure, which, in turn, decreases the life of the engine.
Clean the oil off the bearing with the shop rag.2
Locate the number near the end of the bearing. The notation will either be STD or have an number that looks like this: 0.30. If you have the letters STD instead of numbers, the crank has not been turned and it is using standard bearings. If the notation is a number, the crank has been turned. .030 means the crank has been turned 30 thousandths of an inch. .060 means the crank has been turned 60 thousandths of an inch.3
Write down the number. You will need the number for the machine shop. The shop will turn the crank as much as needed, but depending on how much the crank has already been turned, it may not be able to turn it anymore. If you are simply replacing the bearings and not turning the crank, you will need the number to order new bearings.