My second motorcycle was a well-worn 1952 AJS 498cc single that had been raced in the desert. Riding it at steady speed, I could feel the series of combustion thumps that was propelling me. English motorcyclists liked to say that such engines "fired at every telegraph pole."

Although I could feel the thumps, they had lost a lot of their severity before reaching the rear wheel’s sprocket. A cam-and-saddle torsional shock absorber backed by a truly mighty spring was located on the crankshaft and made as part of the primary drive from engine to separate gearbox. Just looking at it gave me the willies: What if, somehow, I caught my finger in that thing?

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.

At the dawn of motoring, progressive builders tried to substitute roller chain drive for the leather belts originally used. The chains shed their rollers or soon broke from the shock loading of the engine’s combustion events. Belts survived because they slipped rather than transmitted those shock loads.

When some form of torsional shock absorber was placed between engine and driveline, roller chains did become capable of surviving motorcycle service. That was the origin of the cam-and-saddle device on my battle-fatigued AJS.

When Edward Turner in 1937 introduced the definitive British twin, the 498cc Triumph Speed Twin, the problem of smoothing engine delivery was cut in half. With two cylinders instead of one, there were now twice as many power pulses, each half as large. Even so, there was still some need for torque smoothing, so you will find springs or rubber elements built into the clutch outer baskets of motorcycles to this day, replacing the crude-but-effective cam-and-saddle.

Triumph Speed Twin engine
Edward Turner's definitive Triumph Speed Twin delivered twice as many power pulses, each one half as large, as the author's AJS single. Yet there remained a need for torque smoothing that continues with motorcycles manufactured to this day.Cycle World archives

When my little four-cylinder car encounters a grade and its engine rpm is pulled down to maybe 1,300, I begin to feel the “unsmoothness” the instant before the transmission shifts down. Engineers at General Motors call that unsmooth feeling “chuggle.”

Even with a great many cylinders there is still a need for torque smoothing. The great Rolls-Royce Merlin V-12 of 1,650ci, which powered Spitfires and Hurricanes in the 1940 Battle of Britain, had a slender quill shaft, some 11 inches long between the engine’s crankshaft, receiving six torsional firing thumps per revolution, and the reduction gear that drove the propeller. Without that shaft’s springiness in twist, those reduction gears would quickly have failed.

When a cylinder fired, the crankshaft accelerated, slightly “leaving behind” the counterweight, which swung on its pivot, storing some of the firing’s energy.

In radial piston aircraft engines with as many as 18 or even 28 cylinders, the problem was handled in another way. Instead of helical or torsion springs in the drive, the crankshaft was given massive pivoted counterweights. When a cylinder fired, the crankshaft accelerated, slightly “leaving behind” the counterweight, which swung on its pivot, storing some of the firing’s energy. As the gas pressure from that cylinder firing faded away, the weight swung the other way, now giving that stored energy back to the crankshaft. This form of smoothing—always a result of intensive physical testing—was effective in protecting springy steel or aluminum propellers from torsional excitation that would otherwise have fatigued and broken their blades.

In the off-season of 1992–’93, Honda discovered the “big-bang effect” that increased rear tire grip during acceleration off corners. Engineers found that firing all four cylinders of an NSR500 two-stroke racing engine within 68 crank degrees (instead of one every 90 degrees or two every 180 degrees, as previously) allowed the rear tire to recover its grip in the 360 - 68 = 292 crank degrees that were “quiet” with no cylinder firings.

That was all well and good, but the resulting shorter-but-more-powerful torque pulsing destroyed primary and gearbox gears, and made clutches slip. All those parts had to be strengthened or replaced often to survive the intensified torque pulsing. I well remember at Valencia, Spain, in the early 2000s, the beginning of today’s four-stroke era, seeing a green-suited Kawasaki crewman emerging from a team 40-footer with that day’s new replacement clutch gears in his hands.

This is yet another area in which the smooth torque delivery of electric motors offers real advantages. Now if only batteries could become lighter, cheaper, safer, faster-charging, and longer-lasting. Worldwide, thousands of researchers have been working on those problems since 1992.