2015 KX250F engine knock

YZ441
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YZ441
The bike has 5.7 hours on it. Took it for its first ride in over 3 months today and about 20 mins into the ride the throttle stuck wide open, so I killed it. Then I kicked it back over and heard a decently loud knocking in the engine. Anyone have any ideas what it could be?
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YZ441
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YZ441 6/15/2016 11:53am
6/15/2016 11:53am
So I took the valve cover off and I think it might have jumped a tooth or two but I'm not sure. I've heard these bikes went to a hydraulic chain tensioner instead of a mechanic one which sounds terrible
YZ441
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YZ441 6/15/2016 10:35pm
6/15/2016 10:35pm


Found this piece sitting on the piston, have no clue what it's from

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YZ441
Profile picture for user YZ441
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1498
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9/5/2008
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St Petersburg, FL, USA
YZ441 6/15/2016 10:36pm
6/15/2016 10:36pm


This is the head, was a brand new head but now has that gouge in it. Should I invest in a new head?
Bruneval
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Bruneval 6/16/2016 11:32am
6/16/2016 11:32am
An engine builder will be able to give a better opinion, but I had a similar thing happen to my KXF. It revved up on its own so I killed the throttle and pushed it back to the pits. Luckily I didn't keep it running any longer as a bit of valve guide had broken and dropped into the cylinder, causing similar damage to what you have. I would remove the valves and inspect the guides.
jaredkeller96
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jaredkeller96 6/17/2016 9:31pm
6/17/2016 9:31pm
That head will be fine. not sure on your problem. just have a reputable engine builder resurface that head. I've seen some nasty heads that i thought were paper weights come back to life

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