What is an engine crank shaft?
The crankshaft of an engine is the part that turns the reciprocating motion generated by the engines pistons to a rotary motion, the rotary motion is usually output via the engines flywheel. This power in the case of a diesel generator is used to turn an AC alternator.
How does an engines crank shaft work?
In order to do the convert between two pistons reciprocating motion and the rotational motion of the crankshaft has a “crank throw”. This is a surface whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach. There is a great image on Wikipedia of how the pistons and crankshaft interact.
What is a crank shaft made of?
An engines crank shaft is usually made of vanadium micro-alloyed steel. This type of steel can be air cooled after reaching high temperatures while reaching high strengths without additional heat treatment. Additional heat treatment will still be applied to harden surfaces where the bearings contact. Having a low alloy content makes the material cheaper than high alloy steels, which can be prohibitively expensive for mass produced engines.