2010 KTM vibration after new top end

I just had a shop rebuild the top end on my 2010 KTM 250xcfw. We went a 2 millimeters over sized Wisco piston. The bike runs great and has great bottom end but there is now a strong vibration in the handle bars. I even use Flex bars which havent changed from before the rebuild. Any thoughts on what could be causing the vibration?

Check all of your motor mounts and any other bolts.

2mm oversized is a large difference. Any big bore kit I have installed without balancing the crank to match the new piston has resulted in more vibrations than stock.

But this simple" installed a 2mm oversized piston" has me a bit worried. Did the shop have the cylinder bored out 2mm larger then replate professionally? Or did they just bore and install a new 2mm oversized piston into your now new ticking time bomb?

Please elaborate.

The cylinder was bored them replated by the replating shop,A Wisco 2 mm over piston was installed. Nothing was done to the crank. I checked all the motor mounts and only found one bolt that I could tighen just slightly more than it was. I may want to find a used stock top end and go back to orginal specs. This is getting expensive cuz it cost me $920 for the first rebuild.

Why did they decide to bore out the cylinder and replate?

The larger piston and un-balanced crank is definitely your issue. I wouldn't worry about it too much though.

It was my dumb idea that I suggested to my engine builder. He did not mention that I could have this issue. The bike has much more bottom end now. I will take you're suggestion and not worry about it. This is a learning experience.


I would be concerned about a strong vibration myself. Especially if you have Flexx bars.

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