Cast crankshafts are typically used in low-horsepower applications. They are the least expensive to produce and wind up in all but high-performance vehicles. Steel crankshafts are capable of handling a lot more twisting force and higher rpm than a cast crankshaft. A cast-iron crankshaft is made in a mold, after which it is installed in a lathe and ground to specifications. A steel crank is forged and twisted and hammered into shape.
Look at the counterweights on the crank. A large parting line with grinding marks on it is indicative of a forged steel crank. That is because it was forged and bent into shape. The cast iron crank will always have a very thin straight line on the counterweights. This shows where the crankshaft was separated from the mold. The thin line is the parting line between mold halves.
Read the casting numbers and call the dealer for confirmation. Look for an engine with four-bolt main bearings and you will very likely have found a forged steel crank. Most all four-bolt-main engines were performance engines that included a forged steel crank.
Look closely at the surface of the crank. A forged crank has a relatively smooth surface, while a cast-iron crank has a pock-marked appearance and a rough surface.
