Rotary Engined Motorcycles

John H Glimmerveen Licensed to

On the face of it, rotary engines are ideal for motorcycle applications. The free revving nature of these engines, combined with limited moving parts for the combustion process, augured well for their success. However, to make these engines suitable for street bike riders, the final design of these machines was often complex and the bikes relatively heavy. For example, Suzuki’s GT750 and the RE5 had identical weights of 507 lbs or 230 kgs).

The Rotary engine is simple in design; therefore, it should be reliable. Unfortunately it has a number of inherent problems. Included in these problems are apex sealing issues, overheating and the exhaust emissions. Ultimately it was the exhaust emission problem that led to all manufactures discontinuing rotary engined motorcycles.

Original Design

The rotary engine was designed by Felix Wankel, an engineer from Lahr in Baden Germany. He first patented the design in 1929 but it was 1951 before he found the necessary funding to further develop it at the NSU factory. The first operational prototype ran in 1957. The design was licensed to a number of automobile and motorcycle manufacturers including Curtis Wright in the USA. Ultimately it was only Mazda who managed to overcome the inherent tip sealing problems sufficiently to produce vehicles using the rotary engine in large quantities.

The first motorcycle to be produced and offered to the general public was made by IFA/MZ in 1960. The MZ factory had taken out a license from NSU as they thought the rotary engines could eventually become a replacement for their 2-stroke engines. The project began in 1959 and resulted in a water-cooled, single rotor engine of around 175-cc (note: at this point in time, the actual cubic capacity was debatable as the congenital methods applied to piston engined motors did not apply). The model designation was the BK351.

Credited with the design and developemtn of this first rotary motorcycle were engineer Anton Lupei, designer Erich Machus, and research engineer Roland Schuster.

A number of motorcycle manufacturers attempted to sell rotary engined machines, including DKW and Suzuki, and famous English manufacturer Norton.

First Rotary Motorcycle

The first rotary motorcycles to go into production were from DKW in 1973, with their Hercules W200, and Suzuki with their RE5 in 1974. Neither of these machines proved to be reliable, and as a result, they were not popular with the buying public.

From 1983 to 1988, Norton produced a rotary engined motorcycle for use by the UK Police force. The total production is estimated (factual records are not available) at some 350 units.

Norton also produced a street version of the Interpol machine with the model name P43 Classic. Only one hundred of these machines were produced by the Norton factory from 1987 to 1988. Norton returned with another rotary engined machine based on their highly successful works John Player Special racers. The street version, the P55/F1, was offered to the public in 1990 and 91. (The Norton team won a TT in 1992 with rider Steve Hislop riding the rotary engined machine).

Any classic enthusiast considering purchasing a rotary engined classic must be prepared to conduct thorough research before buying. Spares availability for rotary engined machines is not good, due primarily to the limited quantity produced. In addition, rotary engines are prone to rusting internally if not professionally prepared for storage—any attempts to start these engines before disassembling and checking the rotors and apex seals will lead to serious damage.

Prices for early, rotary machines in excellent condition are increasing due mainly to their rarity value. For example:

Suzuki RE5 1975 $9,000

Hercules W200 1975 $7,500

Elsewhere on the net, Norton racer on dyno: