The Two Stroke
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
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.