Connecting rod The connecting rod is fitted between the crosshead and the crankshaft. It transmits the firing force and together with the crankshaft, converts the reciprocating motion to a rotary motion. Made from a drop forged steel. In older engines the connecting rod terminates in a flange known as a Marine Palm, which is bolted to the split bottom end (crankpin) bearing, whilst at the top another flange is formed on which bolted the two crosshead bearings.

Connecting rods in later engines are produced as a single drop forging, incorporating the top half of the crankpin bearing housing and the bottom half of the crosshead pin bearing housing.In older engines, the bearings were white metal thick wall bearings, scraped to fit. Clearances were adjusted by inserting and removing shims between bearing halves. Modern bearings are “thinwall” type, where a thin layer of white metal or a tin aluminium alloy is bonded to a thin steel shell backing. The clearances in these bearings are non- adjustable. When clearances reach maximum limit, the bearing shells are changed as a pair.

Oil to lubricate the crankpin bearing is supplied down a drilling in the connecting rod from the crosshead. When inspecting the crankpin bearing and the main journal, it is a good practice to check the crankpin and main journal for ovality. If the ovality is excessive, it may lead to failure of hydrodynamic lubrication.