Which engine component converts reciprocating motion into rotary motion?

The component that converts reciprocating motion into rotary motion is the crankshaft. In an internal combustion engine, the pistons create linear (reciprocating) motion as they move up and down within the cylinders. The crankshaft is designed with an offset mechanism that transforms this linear motion of the pistons into the rotational motion required to turn the engine's output shaft. This rotary motion is crucial, as it ultimately drives the vehicle's wheels or powers connected machinery.

The camshaft, while also important in the engine's operation, primarily controls the opening and closing of the engine’s valves through its rotation but does not convert reciprocating motion into rotary motion. The timing belt is a mechanism that synchronizes the rotation of the crankshaft and camshaft but does not perform the conversion of motion. The flywheel serves to store rotational energy and smooth out the engine's operation but, like the timing belt and camshaft, does not directly convert the pistons' reciprocating motion into rotation. Thus, the crankshaft's role as the key component for this conversion is essential for the functioning of an internal combustion engine.