Blown Motor

My buddy picked up this 2000 kx250 knowing it was blown i looked it over seemed like a good deal $900 canadian. the rest of the bike is like new! Just needs a top end bottom was jsut done.

My question is what do you think caused this, my educated guess its piston slap, that who ever did this motor last time bored the cylender bigger then the spec should be for the piston causing it to slap aorund and score the hell out of it. Also the ports were never chamferrred, so it would act as a razor to cut the piston too. just my guessing though lemme know what you pros think!!!!

Picture:

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Thanks guys

Oh also im thinking it would be better for him to just put a steel sleeve in it rather then get it re nickel cil job for it just because if he pops it agian he can just go 10 thow over...

which way would you guys go, he doesnt race, prolly put on a few hundred hours a year riding 3-4 times a week trails and fields with friends.

thanks

looks like mine, like it ate something. do not sleeve it regardless of use. replating is better, and the same money if not cheaper

The photos aren't very clear, but it looks to me like the cylinder already has been sleeved?

The damage appears to me to be the results of a "cold" seizure. But like I said it's hard to tell from those photos.

Theres no sleeve in it as far as my eyes can tell.. just has a ring around it from the gasket.. looks like the nickle coating its pealing off in spots though too!

Also what is a cold seizure how does that work? only ever heard adn understood a hot seizure melting of the piston. thanks

I took some morepictures, its a new camera im just learning how it works haha sorry for the bad pictures!

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A cold seizure is where the rider doesn't warm the bike up sufficiently before jumping on it and reaming it out hard. The sudden high loads heat the relatively low mass of the piston much quicker than the much greater mass of the water-filled cylinder casting, so the piston expands faster than the bore and literally wedges itself in.

From the second set of pictures, it could also just as easily be the previous owner just installed a new piston in a worn out cylinder, and the resulting slap combined with worn-thin plating caused the plating to give up the fight and peel away.

well he did re-do the bottom end and the piston looks liek new to me still and he said straight up i didnt have the cash to send it out for nickle plating so i jsut through it back togethor and got a few months out of it.. so that is probably what happend then!

Oh well we knew it was blown up, now my buddy just needs to decide on what rout to take ot fix it.

It does have some really deep gouges out of the cylender i dont know if that can be fixed then re nickled or it would need a sleeve im not sure! but thanks for the answers always like learning!

well he did re-do the bottom end and the piston looks liek new to me still and he said straight up i didnt have the cash to send it out for nickle plating so i jsut through it back togethor and got a few months out of it.. so that is probably what happend then!

Oh well we knew it was blown up, now my buddy just needs to decide on what rout to take ot fix it.

It does have some really deep gouges out of the cylender i dont know if that can be fixed then re nickled or it would need a sleeve im not sure! but thanks for the answers always like learning!

As long as the casting isn't broken, it can be welded and re-plated. Don't sleeve it, that's a terrible way to repair a cylinder.

alright thanks for the tips man

send it out for a big bore lol.

Thats a fair deal. I also bought a 2000 with a blown top end, the bottom end might be ok but Im not taking a chance, going to redo it too. The rest of the bike is great except the plastics and a tweaked rad. Has a few goodies, fatbars, gripper seat,handguards, fmf pipe, gold chain. Got it for 700 cdn.

All fixed up and running it should be worth $2500-2900 here.

That cylinder is FUBAR.

The section above the window on the piston looks brand new. I agree with Chokey's last post.

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