kx250 piston problems

[kx2502009]

i just did a complete rebuild on my kx250 crank bearings seals and such i had the cylinder bore to 1.1 oversize since it has been sleeved and he said he shaved the power valve to clear so i put the new piston in and right where the power valve is with the piston is 2 deep wear marks and stuck both rings the valve doesnt seem to be sticking out what could be my problem and only 10 mins on bike and realized loss off power went threw 3 pistons at 160 a pop need help thanks

 

[whenfoxforks-ruled]

I would say who ever fit the piston/bored it and cut your exhaust valves, owes you a new top end. Its seemingly ruined by whoever? Getting the bore plated is out, the exhaust valves may not fit? I would have sent it to Forward Motion to begin with, no sleevers. Either way, you need a professional to fix and fit a piston. The bore may be still fixable without more boring. Depends on exactly what rubbed the piston. And the bottom end needs to be cleaned thoroughly. You lost a top end, metal was moved, I would not feel safe without splitting the cases. Vintage Bob

 

[kx2502009]

he claims he knew what he was doing and many people have told me about this guy and i was going to get it replated but i just used the sleeve one last time then send it to be replated i stuck a metal ruler to see if it was hitting like he told me to and it wasnt sticking out could he have shaved to much off and caused failure

 

[kx2502009]

here is a pic of my piston any help would be greatly apreciated

 

[madmike90]

maybe the edges of the cylinder surrounding the exhaust valve ports weren't chamfered?

 

[kx2502009]

he said he did that but i know a lot about 2 strokes but have no clue about machining he didnt have the pin for the power valve to hook it all up and he didnt call and tell me he needed it so he guess on how far to shave the power valve but its clearing so can you shave to much off and cause this

 

[julien_d]

he said he did that but i know a lot about 2 strokes but have no clue about machining he didnt have the pin for the power valve to hook it all up and he didnt call and tell me he needed it so he guess on how far to shave the power valve but its clearing so can you shave to much off and cause this

Wow. Can you translate that for us? Perhaps with some punctuation and grammar corrections? You don't want to make us North Carolinians look bad ;)

It's hard to tell from the picture how excessive the damage is, or what could have possibly been the cause. Bob is almost certainly correct and the top end is going to need some machining. SOMETHING interfered with the piston. You should be able to inspect the exhaust valves and cylinder and figure out what it was. Doesn't much matter though as it's going back to the machine shop regardless, right?

J.

 

[kx2502009]

the cylinder is in great shape still did not hurt it just got it bored and i only rode it for about 10 mins but he prolly wont fix it he'll try and say its my fault but can the valve be getting hot and expanding and catching the rings

 

[julien_d]

You really can't get that kind of damage to the piston without it rubbing against something else. That "something else" will show some wear marks too. Look again.

 

[whenfoxforks-ruled]

You may have ground the wrong area of the exhaust valve? The pic is impossible to use. Manually work the exhaust valve? If the sleever did a decent job, they should finish it for you? You will need a new piston, ring, clips and gaskets. That much I can see in the pic! Vintage Bob