I know BSA stated 13 HP for the M20 and 15 HP for the M21. Has anyone ever had a bike on a DYNO and measured the real power our bikes make? I am guessing a M20 really only has about 10 HP.
I think that's a how long is a piece of string question, if you rebuild an engine properly there shouldn't be any reason why it can't be returned to near its original performance, as soon as any wear starts the figure drops, but I imagine there are some quite happily motoring on with less than 10.
It's actually Brake Horse Power Bruce. From memory, the M20 was 12 and the M21 was 13 1/2 with the highest powered British WD solo bike during the war being the Matchless at 16 BHP. Ron
That horse power quoted would be at the crankshaft so at the rear wheel will most probably under 10 BHP. When riding an M20 you have to have nothing to do and all day to do it.
