Strokes of genius

The article ’Different strokes’ (The Engineer, 8 February) on the twostroke engine’s possible renaissance paid scant regard to the two-stroke motorbike.

The remark, ’most motorbikes are pretty simple where the exhaust and transfer parts are open’, ignores the work of Ernst Degner, who was East German MZ’s chief designer and who pioneered the disc valve; this effectively controlled the inlet and exhaust timings and was used bythe likes of Yamaha on its racers and LC twin road bikes.

The reed valve was also used on other bikes to give some control over the inlet port. Finally, there were the pre-war DKW supercharged three- cylinder two-stroke racers.

John Holland