The thick diagonal rod shown here is the connecting-rod of a steam locomotive. The horizontal beam that it connects to is that of the coupling-rod.
(Left to right) At the base of the connecting-rod there is an attachment (incomplete) called the 'big-end', that connects the whole assembly to the crank-shaft. The connecting-rod joins the 'big-end' to the piston (cylindrical object), of a diesel locomotive, via the gudgeon pin (clearly visible in the piston's side).
Photo by Frédéric Bisson.
An example of how a connecting-rod moves.
A connecting rod, or conrod, is a rod that literally connects one mechanical part to another in certain locomotives.
Steam Locomotives[]
In steam locomotives, the connecting-rods are used to transfer power from the pistons to the coupling-rods; therefore transferring the power to the wheels.
Diesel Locomotives[]
Diesel locomotives use connecting-rods in their internal-combustion engines. The connecting-rod is used to connect the piston to the crank-shaft. The connecting-rod is attached to the piston via the gudgeon pin, and is attached to the crank-shaft via its 'big-end' (a metal ring made in two halves).
Electric Locomotives[]
Some, older (pre-1955), electric locomotives have connecting-rods between their traction-motors and coupling-rods.