Just got hold of a pattern M21 piston, no markings apart from oversize stamp. Comes in a plain white box with rings /pin and clips which are wire type. Anyone got any idea where these are made?. I have weighed it against a genuine bsa piston and it weighs lighter. I know it not a Gandini piston or a JP piston..Just concerned about the piston to bore clearance....
It sounds like the ones I have used before...Manufactured somewhere east of Dover...I didn't have any issues with clearances and applied the standard tolerances.
However, I found the ring sets weren't too good, so replaced them with originals which were dimensionally a match...Ian
Cheers Ian. I have a set of hepolite rings to suit and as you say they are a match with this piston, I have a 4.5 thou piston to bore clearance on a rebored barrel ..
I got a piston assembly as you described a couple of years ago from NSA motorcycle parts in UK. That came in same white unmarked box. They advised me at the time they were sourced from abroad and had no issues with them. I have mine fitted and had it running and although not on the road yet so far okay. I gave it the clearance recommended by BSA and there is no slap and runs as quiet as these run. I used the rings supplied, as I don't do a lot of miles probably outlast me.
