Kev,,,My old man put a heap of time in with the old guy (Frank) who used to work for Laurie at JP years ago, & they basically produced a pretty good piston from both the "S" one & the old datto 1200 one,,,then there were a few issues with the ring lands breaking very early in the peice as they were a little too close to the crown & a bit thin in the land,,,they then dropped all the rings down a fair bit & spaced the lands more to make them way thicker,,,we`re now on (i think) the 5th design piston & have stuck with it now for many many years,,,it`s pretty dam good & i don`t believe you can break em...,,,BUT!!!,,,,that piston design is only on the 73mm ones,,,i don`t think they have changed their """Normal""" 1275 & oversize pistons to that design tho
i`ve run my 1415cc stroker speedway mini with those JPs in it up to 9000rpms nearly every sat night for about 4 years solid (with a "re-ring & bearing" job every year tho) & those pistons are still good & still in that same engine & is still quite a good runner, altho they do have a little more clearance now than they used to, but it`s because of that it`s still a good hard race donk
It`s the small bore pistons that are no where near as good a design as the 73mm ones, i won`t use the small bore ones for that reason & i know heaps of people who bag the crapper out of em too & therefore , heaps of people feel that the big bore ones are bad also, add to that, is the ring lands cracking on the early-er 1275 pistons, end result was that JP ended up with a bad name for mini pistons because of all that,,,but i can assure you that the 73mm ones that my dad designed with Frank are actually the bees knees
