JS lightweight racing piston checkup

Just got these photos from a racer who is rebuilding his motor after a season of racing due to a fluke ignition timing failure that caused a massive backfire that split the cases. Note that there is no evidence of unusual wear or piston rocking. You can see normal racing condition wear on the skirt where the piston tightened up when hot - but no scuffing to worry about. The piston being sufficiently tight in the bore prevents rocking.





Racing is brutal. Anything can break and everyone has different failures & breakdowns. Cranks, cams and cylinder bores wear out at an accelerated rate. But the JS lightweight pistons have held up very well when run at reasonable compression ratios and ignition timings.

Edited post.

Good info Jim, Thanks for posting it. More importantly, thanks for producing and making available your quality products for our bikes !! I've said it before but I'll say it again... I believe there's never been a better time to own & ride a Snort'n Norton

Yeah man them racers are seriously hard hearted rascals and with 36' spark adv for sure was running in significant detonation range, but so what ya can't got back and win a race memory but sure can buy more elite engine parts. Good to see how well this instant race case held up. Any exam of the bores? I talked Canaga into a tricky tapper bore on Peel, .001"ish wider at bottom of cooler bore to fudge binding a bit more. Maybe long term solution has nothing to do with the JSM pistons but the concepts of bore clearances needed in all out heated piston jerking. Likely just some hard carbon crust getting down the bore that caused the piston wall scatches. There is a way to drill oil holes that concentrate oil in that hi load area so significantly reduces wear and friction.

Jim, is that piston with gapless middle ring?

Steve

SteveA said:

Jim, is that piston with gapless middle ring?

Steve

Click to expand...

Yes

You can see the thin 2nd ring on the bottom - two rings in one groove.

I would have thought that with the long stroke, the piston would be less likely to rock. In a short stroke motor the angularity of the rod is much greater, and the fore and aft loads would be greater. The higher revs would be more likely to produce rattle ?