BSA M21     BSA M21


April month BSA 2009



I bought my first BSA in 2003 and I still find more and more special things about it.
I purchased the M21 by Morten from Måløv on the Danish island Sjælland. Mortens father bought the BSA in England
and run the motorcycle home to Sjælland. The bike has been running as a service bike by AA and then sold to Mortens father.
There was never paid tax of the original frame, so all the parts are moved to a Danish frame from 1954.

The first special I found out about the bike was that my M21 had no cush drive. Of course it should have one, and I found a used one.
It didn't fit. Pivotal role was too short and thin. The cush drive was thrown into a box where it remains today.

The next special thing I discovered was when I had new clutch plates. My clutch is a spring 4 which I have been told not belong on an old
1 cylinder. But together with the lack of shock coupling gave little sense, since there is a rubber cush drive in the clutch center.

After some years I discovered that there were some "special" M21 models'61 -'63 where there was on cush drive on the pivotal role, but a 12V alternator.
I immediately checked the engine number and indeed there stood BM21A which confirmed that it is an alternator model I had bought.
Suddenly what I thought was somewhat grouped rigging, was a rare M21 model, only produced from 1961 to 1963. The last strange thing I encountered is that my M21 has a 3/8" inch rearchain and according Francois & Frederik and my spare parts manual it should be 1/4" inch.
But Frederick also said "the Svingarm model B31/33 uses the big chain ..." But it would not surprise me now that my M21 is built in the 60s, that they had given it the same rearchain as the B31/33 with svingarm from the 60s. If anyone holds a spare part manual on the M21 generator model, I am VERY interested.
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Translated from the Original 'BSA of the Month' by the danish BSA owners club