My BSA M21
BSA of the Month in April 2009
I have for many years felt that old motorcycles are
Especially the old English motorcycles with their bold sound I find more exciting
than the Danish 4cyl Nimbus.
I wanted a big slow engine with great torque, like a 1 cylinder. So the choice
fell on the largest single cylinder model BSA ever built. The M21!
I found a reasonably neat and running M21 on Sjślland (DK).
On closer examination I found the M21 was not original, built with a little of
this and that from various bikes.
There was no cush drive and the clutch was from a much later model.
After some searching I discovered that what I have, is a BSA M21A, A =
The BSA factory had changed the crank and clutch to make room for a 12 volt
generator / alternator.
The Alternator model was only produced and sold to the AA roadside service in limited numbers from 1961-63.
It was delivered to military service without badges and knee rubbers.