Hi Gents, new to the game but overly enthused to jump in. Just found this bike and totally intend to keep and ride. No plans to do a full restoration. Get her cleaned, tuned, legal, and ride it. It’s pretty much original but rough. But it will run. After much research, I’m still confused. It’s a rigid frame but has a BM20S.....frame prefix. Wasn’t this for plunger models only??The cast motor prefix is BM21.....So I am a little unclear if it’s a 1953 or 54 M21. Any help is appreciated!
'B' prefixes cover three years of manufacture (1953,'54,'55), the particular year being determined buy the actual numbers...So for a more definitive answer on that you'll have to provide the numbers...If you don't want to do that here, though there's no reason not to, you can contact me off forum...
The 'S' suffix indicates 'sprung frame' which is a plunger model as you suspected...So, assuming the frame hasn't been restamped you have a plunger frame front with a rigid rear frame and other parts fitted to it....Plunger and rigid 'tele fork' frame fronts are dimensionally identical..Earlier girder fork frame fronts were different...
In terms of desirability the rigid frame versions is the more sought after generally...Ian
