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Help diagnosing damage to my KX250 motor

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Hey guys.  I'm brand new to this site so, excuse the beginner questions...

 

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 and opted to not reinstall knowing it needed to be replaced.   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 month 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 and possibly a cylinder sleeve.

Thanks,
Todd

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I think he probably meant the wristpin bearing. It's the one that goes between the piston and the piston pin and allows the piston to move forwards and backwards. I don't think it's common for it to fail, much more likely that one of the clips that hold the wrist pin came out.

 

At any rate how does the head look? does the crank rotate now that you have the head off? is there any up and down play in the crank?

 

You can check it by pulling the rod up and tapping on it with a plastic mallet or dead blow hammer, then do the same thing pushing down on the rod. If you can feel any play or the noise it makes changes you probably need to rebuild or replace your crank.

 

I'd get it the cylinder replated before sleeving if the damage isn't too severe.

 

Post up some pictures if you can. Everyone loves pictures.

 

 

 

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"Wristband", I think I'm gonna start a band and call it that! Our first single will be "Fool INjection"!

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I think he probably meant the wristpin bearing. It's the one that goes between the piston and the piston pin and allows the piston to move forwards and backwards. I don't think it's common for it to fail, much more likely that one of the clips that hold the wrist pin came out.

 

At any rate how does the head look? does the crank rotate now that you have the head off? is there any up and down play in the crank?

 

You can check it by pulling the rod up and tapping on it with a plastic mallet or dead blow hammer, then do the same thing pushing down on the rod. If you can feel any play or the noise it makes changes you probably need to rebuild or replace your crank.

 

I'd get it the cylinder replated before sleeving if the damage isn't too severe.

 

Post up some pictures if you can. Everyone loves pictures.

I only took off the cylinder head to look down the cylinder.  I'll take the cylinder off this weekend and see if I can get the crank to move at all.  I'll post pictures as well.

 

Thanks for the advice.

 

Todd

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