What would be a tolerable amount of loss? Or should there be none at all?

Was talking to someone who had oversized pistons put in, and one of the cylinders was bored to much and the piston is not seating properly. He's losing 15%. Just trying to get an idea how bad that is, and if there is a possibility of maybe putting a bigger piston in place to fix it. He doesn't know what size piston what put in, so I don't know if there is even a bigger one available. Just trying to see exactly how bad the loss is.

are you sure his valve train is off line?

Don't even know what that means. Does that mean that they didn't bore it out properly centered?

No, it means to make sure his rockers are loose and de push rods are out de way!

Yeah, I think they did the test properly if thats what your asking. Lets assume that they did anyway. And lets assume they already know the job on the cylinder was botched from looking at it after the leak down. Kind of a third party deal, and I don't have a whole lot of info. But what is tolerable, and how bad is 15%? You think it could possible be taken to someone who knew what they were doing to repair it?

he said it still has the stock pistons, he jus shaved one cyl and im guessing just put the piston back in, i dont know much about small engines but recently i done a top end on my dirtbike and i put in an oversized piston and didnt bore it any!

so a stock piston in a shaved cyl would have to leak! but he said the cyl was bored unevenly was why it was leaking.

i dont see why i couldnt have each cyl bored the same and properly and put in oversized pistons and be done!??

I am currently running a 14% leakage on my motor and it runs fine yea i did loose a couple of MPh on top end, its been this way for 60 hrs now and it stills runs strong. Me personally i would have the guy who did the work stand behind his work and rebore and order the correct size pistons for the bore job