The was a time in the early 1970s when the rotary engine really did look like the next big thing. In truth, it had been around since Felix Wankel imagined it in 1919 and patented the idea in 1929, but nobody backed Wankel financially until German automaker NSU in 1957. When the first running engine was built, it was licensed to everyone who expressed an interest, including Citroen, Ford, GM, Mazda, Rolls-Royce and Toyota.

The compact cylindrical shape of the rotary engine gives little clue as to what’s going on inside. A triangular piston with curved sides orbits around a central shaft, while fuel is compressed in peripheral chambers, creating the induction/compression/ignition/exhaust cycle. The piston has flexible tips on its apexes which seal the compression chambers as they pass. It can spin freely far faster than piston engines but generates a great deal of heat, which initially destroyed the rotor tips and required a complete engine rebuild.

NSU sold 2,375 Wankel Spyders from 1964-67, when the company bet the farm on the luxury NSU Ro80 sedan, of which they built 37,398. When many these came back for engine rebuilds, NSU was forced into bankruptcy and bought by VW/Audi in 1969. Mazda underwent similar problems with the RX2, RX3 and RX4 and almost went broke itself before solving the problem in the RX7 of 1979.

Fichtel and Sachs, meanwhile, who had built motorcycles in Germany since 1904, gambled on a rotary engine motorcycle called the Hercules W2000 in 1974. Suzuki built the very complicated water-cooled RE-5 briefly in 1975-76, but Hercules bet on a fan-cooled single-rotor engine of 294 cc. Initial models developed 23 bhp, later increased to 31 bhp at 6,200 rpm. The W2000 was expensive and smooth-running, but it was thirsty, not very powerful and generated enough heat for a crematorium.

The Hercules W2000 weighed 391 lbs, and utilized a six-speed gearbox from a Penton dirt bike. It rode on 18-inch wheels with Ceriani front forks and 11.8-inch front disc brake. Dual exhausts were set low enough to give 6.5 inches of ground clearance on each side.

The first bikes reached the U.S. in January 1975, 34 red bikes and six yellow ones. The rotary sales team signed up dealers, but the $1,900 price proved a deterrent, along with the need to pre-mix oil and gasoline. Introduction of the KC-30 rotary dirt bike in May generated some excitement, quickly quashed by its $2,930 price tag. An oil-injection system was planned for 1976, but news of that slowed 1975 sales even more.

Eventually the project fizzled out, after only 1,784 Hercules W2000 models had been built. Like the Suzuki RE-5, clean low-mileage models aren’t hard to find, but rotary engines require a completely different skill set to maintain, along with different tools and manuals. Just like the rotary cars, they either start easily and run well, or they are stationary exhibits in a museum. There really is no middle ground. The lack of power, lack of exciting noises and limited clearance mean that while the Hercules W2000 is a magnificent topic of garage conversation, the question of whether it represented a technological breakthrough has already been answered.