Referring to Fig.1, in the Illustration No.1, we see a ball “W” revolving at the end of a rod. This revolving ball is unbalanced in that no equal weight is located on the opposite side of the shaft center. Therefore, the centrifugal force sets up an outward pull with the consequent eccentricity of rotation. Vibration will result. In Fig.2, we see a flywheel with a counterweight “W” which would act the same as the ball just described in rotation. Such a weight must have a counter weight to balance it. Fig.3 shows two weights, “W” and “W1” mounted on opposite sides of a shaft center. Of the two weights, “W1” is the heavier. Naturally centrifugal force would be in favor of this heavier weight. This sketch may be likened to the flywheel, rod and piston shown in Fig.4 a simple single cylinder motor. In actual practice the piston, rings, pin and upper half of the rod do weigh more than the counterweight “W”. If revolved in the same plane, that is, just let fly around this mass would be considerably out of balance. We must remember, however, that part of the weight is reciprocating and part rotating and the two masses tend to cancel each other, anyway enough to effect fair running balance of the motor. The single-cylinder motor with its lack of power impulses, is the most difficult motor to balance. Only very high r.p.m. singles can be balanced nicely at top speeds.