What part connects the piston to the crankshaft?

The connecting rod connects the piston to the crankshaft. Its small end attaches to the piston through the wrist pin, while its big end wraps around the crankshaft’s crankpin.

This rod transfers combustion force from the piston to the crankshaft. As the piston moves down during the power stroke, the rod pushes on the crankpin; as the crankshaft rotates, the rod pulls the piston back up for the exhaust and compression strokes. This changes the piston’s straight-line motion into rotational motion.

The connecting rod is not the same as a pushrod or valve stem. Pushrods transmit motion through some overhead-valve valvetrains, while valve stems are part of the system that opens and closes the intake and exhaust valves. The camshaft controls valve timing; it does not connect the piston to the crankshaft.

Connecting rods endure alternating compression and tension, with forces rising sharply as engine speed increases. A broken rod can puncture the engine block—a failure commonly described as “throwing a rod.” Steel is common in production engines, while high-performance engines may use forged steel, aluminum or titanium rods.