I have the parts of a couple of 6 spring BSA clutches but have never been tempted to use them because of the destruction I have seen inside them and they just dont look right engineering wise. That chainwheel double row ballrace and the way it just seems to float around makes me shudder!!! I have four BSA bikes from the 1940s and 1950s all with M20 single spring clutches and as far as I am concerned if the parts inside these are O.K. they are great. Regards to all who have M20 or B31/33. Dave B.