Connecting Rod (Conrod)

The connecting rod, or conrod, joins the piston to the crankshaft. Its small end connects to the piston via the gudgeon (wrist) pin, and its big end wraps around the crankpin. As the piston moves up and down, the rod pushes and pulls the crank, turning linear motion into rotation.

Conrods carry huge alternating loads, so they are made of forged steel or, in some racing engines, titanium. Four-stroke multis usually have split big ends with plain shell bearings; single-cylinder and two-stroke engines often use a one-piece rod with a needle-roller big-end bearing on a pressed-together crankshaft.

A knocking noise that rises with revs can point to a worn big-end bearing, which needs immediate attention. Over-revving, oil starvation and in two-strokes running too lean or with too little oil are the main causes of rod failure.