THE CONNECTING ROD

The Con 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 drop forged steel, on the older engines the bottom of the con 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 is bolted the two crosshead bearings. Connecting Rods on the later engines are produced as a single drop forging incorporating the top half of the crankpin bearing housing and the bottom half of the solid crosshead pin bearing housing. On older engines the bearings were white metal thick wall bearings, scraped to fit. Clearances were adjusted by inserting or removing shims between the bearing halves. Modern bearings are of the "thinwall" type, where a thin layer of white metal or a tin aluminium alloy is bonded to a steel shell backing. The clearance on these bearings is non adjustable; When the clearance reaches a maximum the bearing is changed. Oil to lubricate the crankpin bearing is supplied down a drilling in the con rod from the crosshead. When inspecting the crankpin bearing and journal it is good practise to check the journal for ovality because if this is excessive, a failure in the hydrodynamic lubrication can occur.