What is a crankshaft?

• A. Changes reciprocating movement of pistons and connecting rods into rotary motion
• B. Converts rotary to reciprocating motion
• C. Stores energy
• D. Absorbs torsional vibrations

Answer: (A)

The crankshaft’s job is to convert the up-and-down motion of the pistons into rotational motion that can drive the engine and drivetrain. It accomplishes this with offset crankpins on a shaft; as each piston pushes via its connecting rod, that push rotates the shaft, producing continuous turning motion as the cylinders fire in sequence. The crankshaft may include counterweights to help balance the engine and reduce vibration, but its primary function is the conversion from reciprocal to rotary motion. It isn’t meant for storing energy—that role belongs to a flywheel—and it isn’t the main component for absorbing torsional vibrations—that’s handled by dampers and the flywheel system.