Crankshaft
The crankshaft, sometimes casually called the crank, is the part of an engine which changes the up and down motion of the pistons into rotation. To convert the motion, the crankshaft has one or more offset shafts. The pistons are connected to the crankshaft by these shafts. When the piston moves up and down, it pushes the offset shaft. This in turn rotates the crankshaft.