At each firing of the engine, the pressure energy of combustion was added to the crank. Even though the pair of full-circle flywheels weighed more than 30 pounds, that energy, added to it over roughly one-quarter of a revolution, rapidly accelerated the crank. To prevent the whole bike from leaping forward at every firing, that cam-and-saddle absorber stored a fair amount of the combustion thump by compressing the spring. As firing pressure quickly died away after 80 degrees past top center, the spring fed that energy back into the drive line. This had the effect of smoothing the drive from the engine, converting its short, sharp torque pulses into something longer, smoother, and more survivable.