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M20/21

The big side valve singles. Here are the main differences:
M20 is 500cc and has a cast iron head
M21 is 600cc and has an alloy head and differently shaped piston.

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CLUTCH NUT
15-4312
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Clutch nut M20. This is the central nut in many BSA’s and it has often been hammered!

REPAIR KIT
KET110046KIT
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Genuine wartime Renold repair kit for 1/2 x 5/16" primary chains.
New Old Stock.