Connecting Rod

A connecting rod (often called a rod) is a critical engine component that links each piston to the crankshaft. It acts as a lever arm that transfers the immense downward force of the expanding combustion gases from the piston to the offset journal of the crankshaft. This motion translates the reciprocating (up-and-down) linear motion of the piston into the continuous rotational force that drives the vehicle.

Connecting rods are typically forged from high-strength steel or powder metal to withstand the extreme tension and compression forces of a running engine. The rod features a "small end" (which connects to the piston via a wrist pin) and a "large end" (which splits in half to bolt around the crankshaft journal). High-precision split-sleeve rod bearings are installed in the large end to minimize friction and wear against the crankshaft.

Problems with connecting rods are rare but catastrophic. Insufficient engine lubrication or oil starvation can cause the rod bearings to melt and seize, leading to a "spun bearing" or causing the rod to break. Under extreme stress—such as engine hydrolock (water entering the cylinders) or excessive engine RPM—a connecting rod can bend or snap completely, often punching a hole through the engine block, an event known as "throwing a rod."

Replacing or repairing connecting rods requires complete engine disassembly. In high-performance engine builds, upgraded H-beam or I-beam forged connecting rods are often installed to handle increased horsepower and boost pressure without bending.