I have a "new" cilinder with the standard bore 82 the guy who made this for me is experienced. He told me to remove the lower (oil)pistonring. What remains is two upper rings and right below them one oilring. Is that correct? Why? This guy told me so but couldn't explain why. Anyone who can explain it to me?

email (option): mail@clemensvandussedorp.nl

Those pistons are not the best pistons around, the best thing to do is to get an original BSA piston or a Hepolite piston. Main thing with your piston is that they are to heavy and the lower oil ring might prevent the upper to get lubricated good enough.

Henk

email (option): ahum@quicknet.nl

BSA themselves made M21 pistons with the additional ring at the bottom of the skirt though they aren't very common...

I ran one of those in a civvy M21 for about 8 years without any oiling problems....

If you have an Italian piston excessive weight can be an issue and you should check the weight against an original to determine whether work on the piston and/or rebalancing of the crank is required...Ian

email (option): ian@wright52.plus.com

Never knew about these M21 pistons with an extra ring, never to old to learn it seems.

email (option): ahum@quicknet.nl