BSA M20
THERE ARE PLENTY of contenders for the title of ‘the bike that won the war’ and BSA’s chunky side valve single, the M20, has a fair claim to it. Created by the renowned Ariel and JAP designer Val Page, it filled the hole in BSA’s range for a solid sidecar hauler for the family man in 1937, as well as being built to a military specification, in competition with machines from Matchless, Norton, Triumph and Royal Enfield.
The M20 started out with hand-change gearbox, with the lever on the right, a rigid frame and girder forks. The bottom end design was common across the BSA range of singles, being used on both their M range of side valve and OHV heavy duty motorcycles and the lighter weight B series, including the famous Gold Star. The hand-change suited sidecar usage but was dropped and replaced with a right-foot operated lever in 1939, in a one-up-three-down arrangement.
With the M20’s massive flywheels and low compression ratio the BSA would pull away from a standstill in almost any gear, and once into top would plod along at a respectable rate. The brakes were excellent for the period, for a solo, making the M20 a respectable and practical choice for anyone not in thrall to the gods of speed. Although side-valves were slow, ran hot and were thirsty, they were also bulletproof, would run on very poor quality fuel and didn’t have a great deal in the way of moving parts to go wrong.
The M20 also got a bigger oil tank in 1939, a new toolbox and adrinking a gallon of fuel every 56 miles.
