I ended up sleeving mine back to std commando and fitted a set of wiseco's supplied by Mick Hemmings. It meant the pistons came to the top of the bore as expected and put more meat in the sleeves. I had run several sets of JP's in my 750 race motor and had nothing but problems with them
, I think JP's motto is 'seize the day !' This was in a race application and clearances were very liberal so this couldnt happen. One Piston in the second set I put in was found to be cracked after it nipped up on that side after its first ever brief light run, the other piston was fine. I'm building up another british twin at present and it won't be running JP's! Perhaps they might be ok in a road application
if run in long enough, but I wouldnt touch them myself.