Exploded view - balancer
In an engine with an even number of cylinders (i.e. 2, 4, 6 etc)., a piston on an upward stroke is always counter-balanced by one on a descending stroke. However, in an engine with an odd number of cylinders, such as that fitted to the Rocket III, this natural state of balance does not occur. Therefore a balancer is fitted to the engine in order to control irregular pulses caused by the odd number of cylinders. Without a balancer, the engine would ‘pulse1 each time the crankshaft rotated. This 'pulsing' would be felt as a vibration which would amplify as engine speed increases.
The balancer has the effect of a pair of counterbalance weights, which create an equal amount of energy in the opposite direction, and at the same time as that produced by the crankshaft, pistons and connecting rods. Because the opposing pulses occur at the same point of crankshaft rotation, and are of an equal magnitude, a state of equilibrium or balance is reached.