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.