Doc is right with the triumph 2500 pistons,,,, ususally they are well down the bore tho, so i can`t see them being in there unless someone has decked a good 1/4 of an inch or more off the top of the block,,, anything is possible these days tho, every Tom, Dick & Harry has had a go at reco-ing mini engines & all sorts of wild & wiered combinations have been born
Mine is actually like that tho & i`m using small bore poush rods & shortened head studs
But be carefull tho because there is also the triumph 2000 piston which is the same bore but is quite tall
buy a burette,,, it`ll be the best thing you ever bought
& i can make your cyl head chambers into a bath tub if you need it that way, don`t be scared
Edit,,, Ok so i just re-read your first post,,, It really IS like my 1510 donk , except without the extra stroke
still,,, i can make your head into a bathtub, just give me a stock one that hasn`t been shaved & you`ll be sweet, I`ve got 32cc out of them quite commonly & have actually made a 35cc one years ago & it`s still a runner
I just don`t recomend that you try that at home kids, i really don`t like to see wasted 1275cc cyl heads
