the.com/crankshaft

means The rotating shaft in an engine that converts the pistons' straight up-and-down thrust into the circular motion that drives the wheels.

from Built from 'crank' — an old word for a bent handle or bend used to convert motion, related to Old English 'cranc' (something bent or crooked, the same root family that gave us 'crinkle') — plus 'shaft,' the rod it's built on. Hand-crank mechanisms using bent axles to turn reciprocating motion into rotation predate the automobile by centuries; the engine part simply inherited the name once engineers needed a mechanical crank sturdy enough to survive thousands of explosions a minute.