I've got a shitload of kart pistons on the shelf in my shed with seize marks like that on the exhaust side. From my bucket racing days. It didn't stop 'til I started using a 22mm i.d. tail pipe on the chamber instead of the 18mm I was using before.
What kind of riding are you doing ? Not dirt track by any chance ? If you've got it nailed a fair bit, then any restriction in the exhaust will cause a heat build up-like the power valve for example......Or using the wrong muffler ??.
I'd fix the power valve or just wire it open. Clean up the piston with a smooth file so it doesn't look so horrid. Use some acid on a toothbrush (not your best one !) to get the alloy off the bore-we used to use acid from the swimming pool supply shop I think. You'll need to get all the crud off that's above the exhaust port. Clean up the ring-they are hard as hell and usually can take a pounding. Unless the ring is scored scored then it'll still give you enough compression to run well enough.
It'll probably rattle pretty badly, but Wiseco pistons are tough and can handle a fair bit of clanking around.
Then get it out and cane it. If it seizes again, you'll know it's got nothing to do with the power valve, or the piston-bore clearance.
That's what I reckon anyway.
Nitram
