JP PISTON FAILURES

[@williamnethercott4364]

What are the chances of the same defect happening twice, virtually identical in appearance?

[@thra5herxb12s]

The fracture in the recent piston looks like the land has been pulled apart, almost as if it's shrunk at a different rate from the rest of the piston. It's also broken away from the piston underneath and wouldn't take much to lift it off.

[@Cobra427Veight]

1/2 a thou on the little end or light drag if your reaming it, you get lobe-ing with reamers , that's 6 or so high spots that will soon smooth out and bed in, have you got the oil hole drilled ,in the rod , bummer about piston, your not getting detonation are you .?

[@thra5herxb12s]

This is the third piston that has failed like this. The engine runs fine with a different make of piston which I have to fit after every one of these fails. My spare piston is only low compression and doesn't suit my requirements.

[@Cobra427Veight]

@thra5herxb12s I bought a JP piston for my matchless g80 , it had the wrong piston in it originally ½ down the bore at TDC , it's got .007" clearance , I try it , not to good though to see these fail , I have got another oversize gandini piston , I used to be a automotive machinist, 80s and 90s, if this happens to mine , I could weld the ring lands with some 4047 12 % silicon and re machine the grooves . When I used to pin hole bore conrods, we only gave them, 4 thenths of a thou , but that's a really good finish and gudeon feels loose . Cheers