HEAVY TIME
Recently I have rebuilt a number of BSA M20 engines. After heaving around various very heavy components, I got to thinking. There’s an almost infinite number of ways to produce 13bhp. Any number of small, light, two-strokes exceed this figure with ease. These lightweight motors can be carried by one person, who doesn’t need to be an Olympic weightlifter or a bodybuilder.
Why then did Val Page design the M20 engine for BSA? Overhead valve engines had been around for a very long time and by the mid-1930s had proved reliable enough. The sidevalve design was, I presume, easier and cheaper to produce, although the M20 engine is very heavy. I once purchased an M20 motor at an autojumble. I attempted to carry it, minus magneto and dynamo, from the vendor’s stand to the car park. I didn’t get far before returning and asking to borrow his sack-truck! Even then I had a sore back for a week after lifting it into the car.
The idea was to produce a heavyweight machine capable of pulling a large sidecar. Even in the mid-1930s the clouds of war were gathering over Europe and it became obvious that the British and
