Maintenance & Technical > KX250 / KX125

250f rebuild after piston hit valves - check bearing? replace bottom end?

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ecdeyzel:
I am by no means an expert, but I have also never seen a new bearing spin freely. Only time I have ever seen bearings spin freely is old, dry and worn out bearings bearings with play. As alward25 mentioned, if it moves freely, easily and is smooth when you rotate it with your fingers, I think you might be good. Maybe get a second opinion if you know someone who has knowledge in this to feel it for themselves too, it will help with peace of mind. Or, like you said, replace it to know 100% you are in the clear if you are worried about it.

Ed

alexander-vmann:
i think you can use the bearing, but you could change it to be 100% dont have to change all the bearings tough, the only bearings i have ever heard of the can spin freely without being worn are chearamic bearings, i would be more concernd about the play in the crack/rod is it side to side or up and down play?

KXDINO:
I would be replacing the conrod etc as well to take a hit like that , to crack the bore , it could prevent a disaster down the track.

don46:
If you have it apart to spin the bearings replace them, the crank bearings themselves aren't that much. I would also do the crank, either go OEM or Carillio don't use hot rods for sure. as already said you don't have to replace every bearing in the bottom end, but since it sounds like piston broke and impacted valves, if that is the case you could have a bent rod, might not be noticeable to the eye. I am probably more diligent than most when it comes to 4 strokes maintenance. my race bike gets new valves every year and a new crank every other year (hillclimb bikes) and they probably don't have over 4 hours a year, I know what it costs if I do have a failure and thats not pretty either.  If it was me, I would replace crank, bearings, all the valves and springs.

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