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I bought a '00 KX250 last week. I bought it for a rock bottom price knowing it had motor issues. The bike itself is in amazing condition and has tons of upgrades. I've never rebuilt a 2-stroke so, looking for some advice. When I got it, the seller told me he took the cylinder off and was able to determine the pin in the "wristband bearing" had come out. He thought it needed a top end rebuild and to flush the motor to get all the bearing particles out.

I haven't touched the bike until this morning. I noticed when I got it that I couldn't even kick the motor over, which seemed more than a top end rebuild... I removed the cylinder head and looked down the cylinder and much to my surprise, the seller removed the piston. I'm guessing he did this to investigate the issues. I can see the crank and connecting rod are there. The cylinder has a few scratches but, nothing too dramatic.

I plan to pull the motor later this week but, curious if others hav ever had a "wristband bearing" failure and what kind of damage you experienced. When I bought the bike, I budgeted for a lower and upper rebuild.

Thanks,
Todd
 

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I don't know what a wrist band is. Never heard of that one. Maybe he meant wrist pin bearing? If so, that is not the problem because the piston isn't in and the engine will still not turn over. As long as the case is not damaged, it is rebuildable. Hopefully the connecting rod is siezed to the crank. That's no big deal. Just buy a top and bottom end kit such as this: Dirt Bike Wiseco Top And Bottom End Kit - 2-Stroke | MotoSport
If one of the outer bearings has seized and spun in the case, you will need a set of cases as well.

If your cylinder is scored, send it off to be fixed before you buy a top end kit. This way you know what piston size to choose. This place has a great reputation if you need cylinder repair: L.A.SLEEVE - Services - Shop Services

If you plan on splitting the case yourself, buy a tool for this purpose or borrow one from a buddy: Dirt Bike Motion Pro Crankcase Splitter | MotoSport
I wouldn't attempt it with out the tool.

If this is your first time, make sure to get a manual that walks you through the process. Watch youtube.

Congratulations on the new bike. My buddy just did the exact thing with a YZ250. Picked it up dirt cheap with a sized engine. I will be splitting the case on my CR500 soon too. The tranny likes to shift by it self these days.

Good luck and have fun. 2 strokes are a ton of fun and cheap to ride!
 

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i agree with williams reply, pretty well rip everything apart in order until you get your engine spinning over again, get everything measured (including the taper wear in your jug). if its close to max spec... may as well go with oversize kit for couple extra bucks vs oem size.

I realize this is a couple months old. enjoy :)
 

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I have 3 kx250s that run and 2 parts bikes. They are my favorite. Bike I've done sooo many builds. Great purchase on the kx. The cylinder has a special plating I have gotten away with a very light ball hone. But if you have a scratch of any size it will need to be replated. Melinem does a great job! And specific questions feel free to pm me I have tons of pics.
 
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