Ted Mellors Rotary Valve New Imperial

Ted Mellors was born In Chesterfield in 1907 and went on to become an extremely successful motorcycle racer – becoming 350cc European Champion in 1938.

This quick post concentrates on an unusual engine that was developed by Mellors in the early 1940’s. The base for the engine is a New Imperial single cylinder, but Mellors manufactured and patented his own rotary valve system for it. There was much interest in rotary valves engines prior to WW2, due to the potential benefits of higher compression ratios and mechanical simplicity over conventional poppet valve systems. Frank Aspin was probably the most well known exponent of rotary valves in the motorcycle field during the 1930’s.  

The Mellors rotary valve system utilised two conical rotary valves in the cylinder head; one for intake and one for exhaust. Unusually these rotary valves did not move continuously in sync with the crank, but instead moved in 90° steps. In order to achieve this more complex valve movement, a Maltese Cross mechanism was used. When the valves were in their stationary position a helical spring pressed them onto their housing so they were cooled. Just before the 90° movement of each valve, a face cam lifted each valve of its seat by a few thou. This allowed the valve to be rotated freely without excessive lubrication. The Maltese-Crosses themselves were driven by pins on the ‘cam’.

The Maltese-Cross system of valve operation would have been subjective to very high accelerations. Reliability at high speed and mechanical noise would surely have been major issues.

150cc Bruce Special New Imperial

The Bruce special was built by Charlie and his brother John of Motherwell. It was based around a 150cc New Imperial unit engine, to be eligible for the Scottish 150cc racing class. The full duplex swinging arm frame was a one-off built by Charlie Bruce with help from Joe Potts. Due to the lack of proprietary motorcycle rear suspension units, Charlie converted bomb door jacks that Joe had been manufactured in his engineering firm as part of the war effort and were also used on his 250cc  Velocette MAF.

The ‘Bruce Special’ was raced by John Bruce at various Scottish circuits during the early 1950’s, including Beveridge Park and Crail, as well as sand racing events. In 1952 the ‘Bruce Special’ carried the number 1 plate at the Beveridge Park road races. As the 150cc class was dropped in favour of a new 200cc Scottish class, the bike was converted to a 125cc and run in that event.

The ‘Bruce Special’ was sold by Charlie Bruce to William McBirnie, one of his friends in the Avon Valley motorcycle club. The bike was road registered in 1952, but William continued to enter races at Errol. The bike was then sold to another Avon Valley member, John Miller who used it on the road until 1958, the last time that it ran. In recent years this bike was located and purchased by Ian Whitehead & George Corner.