Forgings or castings. The crankshaft of a marine engine is the main rotating part of the engine. After the connecting rod is installed, it can accept the up and down (reciprocating) motion of the connecting rod into cyclic (rotating) motion. The blank should be a forging or a casting. Its material is made of carbon structural steel or ductile iron. It has two important parts, the main journal and the connecting rod neck. The rotation of the crankshaft is the power source of the engine and the source power of the entire mechanical system.