As the name suggests, this rod connects the top and bottom end bearings, facilitating the conversion of the Piston’s forces into the crankshaft’s rotating power.
The rods are made from a steel forging shaped at each end to accommodate the suitable bearings. The oil hole is bored through the center of the rod to allow the passage of lubricating oil between the bearings-downwards in cross-head engines but upwards in piston trunk engines.
The rod’s length is as short as the design permits to restrict the engine’s general height.
The rod acts mainly as a strut under axial loading in slow, crosshead type engine and is made of round section. Modern practice is to forge one-half of the rod end bearings integral to the top and bottom end bearings.
Earlier designs had flat palms connected to the bearing. The road is subject to transfer of bending forces from inertia of parts in medium and high speed trunk Piston engine and I shaped section girder is more efficient.
The connecting rods of the medium speed engine can be shaped with a flat flange bolted connection, either adjacent to the lower end bearing or at some point along the rod length.
This enables separation so that the pistol can be removed without disturbing the bottom end or, conversely, without damaging the top end or piston, the bearings can be dismantled.
This also reduces the minimum headroom needed for overhaul above the engine.