Suzuki’s Rotary-Powered RE5
When Suzuki released their RE5 at the Tokyo Show at the beginning of 1974 it was an extraordinarily brave marketing move. Suzuki already had their unusual 750cc water-cooled two-stroke triple, but the Rotary was even more unconventional. Company chairman Jitsujiro Suzuki hailed it as “the beginning of a new age in the history of two-wheeled touring.” It was a great call but Suzuki underestimated the conservatism of the average motorcyclist.
Felix Wankel’s rotary was not new, and the idea of a single triangular rotor moving around a figure of eight-shaped housing on an eccentric shaft to provide a four-stroke cycle was appealing.
The engine was extremely smooth and theoretically simpler as there were no camshafts or intake and exhaust valves. But the design wasn’t as straightforward as it appeared. Wankel development had much to do with the demise of the German car company NSU in the early 1970s, and it was a notoriously thirsty engine design. The world was struggling with an oil crisis in 1974 and this hurt the Wankel and the two-stroke.
There was also difficulty in adapting the Wankel engine to a motorcycle and it was surprising that Suzuki persevered with the RE5.
For a design with supposedly one moving part, the RE5 was extraordinarily complex. The single rotor Wankel had two ignition systems and to cope with the extreme heat, dual cooling systems. Both the mufflers and exhaust header pipes had additional ducted cooling.
There were twin lubrication systems and a Mikuni 18-32 HHD two-stage carburettor and unique port valve system prevent exhaust gasses from mixing with the incoming fuel charge. The carburettor weighed 2 kilograms and incorporated five separate circuits. Monitoring and metering these systems was an electronic and mechanical maze of indicator lights, vacuum switches, magnetic floats, thermal resistors, thermostats, regulators and relief valves. There were few cars as complex, let alone motorcycles.
Although displacing a nominal 497cc, the single chamber rotary generated power similar to that of a 750cc machine (62 horsepower at 6,500rpm), with commendable smoothness. Considering the innovative nature of the engine, the running gear was surprisingly conventional, much shared with the two-stroke GT 750. The frame was a conventional tubular steel structure with skinny telescopic forks and underdamped rear shock absorbers.
But the RE5 was a large motorcycle, and with a long 1550mm wheelbase the RE5 tipped the scales with a wet weight around 260kg. Fortunately Suzuki saw fit to provide dual 295mm front discs but the handling left something to be desired and there were other bikes more suited to spirited riding. The RE5 was more suited to touring, only limited by the poor range of the 17-litre fuel tank.
Unusual features abounded. The instruments were contained in a strange cylindrical instrument panel and the taillight matched. A plexiglass cover flicked up to display the instruments when the ignition was turned on. These features contributed to a motorcycle on the outer edges of conventionality and later versions had a more orthodox instrument layout.
But ultimately the RE5 was not only too different for the conservative motorcycling public, it didn’t offer any inherent advantages over more mainstream designs.
Certainly the RE5 was as smooth and comfortable as any tourer on the market, but it was also heavier, thirstier, and more complex.
After investing considerably in the rotary Suzuki then followed a period of conformity, and within a few years most large Suzukis were in-line fours. Today the RE5 is almost forgotten, but remains an interesting relic of a different age.
Many thanks to John Gee of Antique Motorcycles Cheltenham, Vic, for the use of the RE5 pictured.
Five Things About The Rotary
Suzuki signed a licensing deal with NSU/Wankel to develop a rotary engine in 1970. But the seemingly straightforward rotary engine presented many more problems than expected.
To withstand the constant high speed contact between the rotor apexes and the trochoid surface a special hard coating (CEM) was developed. Suzuki also experienced problems creating an efficient cooling system.
Suzuki also included self adjusting three element apex seals to seek and hold the exact tolerances along the inner rotor housing. They also built an entirely new production line with specially-developed machinery.
In Suzuki’s words, “Resolving the mass of design and engineering problems took an enormous amount of time and money.” It was rumoured that because the RE5 was so unsuccessful Suzuki dumped the remaining stock and parts into the Japanese sea.
The only other rotary-engined motorcycles were the DKW Hercules, Norton, and Van Veen OCR. Yamaha had their twin rotor RZ-201 Rotary nearly ready for production but shelved it at the last minute, while Honda tested a CRX Rotary prototype and Kawasaki had an X-99 type Rotary on the drawing board.
Although not a big seller when new there is a lot of interest in the rotary today.
Check out these sites:
This site is dedicated to the RE5 and includes a registry.
This is good:
Here is an RE5 forum:
What’s it worth?
New (1975) $1995 Fair $10,000, Mint $15,000