The crankshaft

How to tell if your crankshaft is cast or forged:

Every Corvair crank made by GM is forged.

• A forged crank has a parting line on it that is 1/2" wide, and every cast crank has a thin parting line, about 1/8" wide. The parting line runs down the length of the crank on the un-machined surfaces.
• A forged one rings like a bell when tapped with a hammer, while a cast crank sounds dull.

A cast crank is made by pouring molten metal into a mold made from sand. The crank takes the shape of the mold. A forged crank is formed from steel stock, heated until it can be hammered into the shape desired, much the same way a blacksmith made horseshoes. The only difference is that the crank was placed in a die, and "hammered", until it filled that die, which is a hardened steel mold. The forging process alters the molecular structure of the part, through compression, delivering a stronger part.