Seized Piston KX250f

MicMcDude375
I was out riding a week ago and my motor stalled out twice while I was in the air over jumps. I thought nothing of it as it bump started back up when I landed. I went to start my bike at my truck and it stalled again, and then when I went to kick it, the kick starter would not move. I took all the oil out and noticed that only about half of what should be in the engine came out. Pulled the clutch apart, and from there I could move the inner hub that spun the transmission, but the outer hub wouldn't budge. So from there I took the cylinder off, and the ring, piston, and cylinder all had some scratches, but that was to be expected. The piston moved freely though, with and without the cylinder on it, and by turning the motor over by the kick starter and flywheel. So I am a little confused to what caused the issue, and is it as simple as just replacing the piston, cylinder, and rings?
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Paw Paw
Profile picture for user Paw Paw
Posts
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Joined
12/24/2011
Location
Benton, LA US
Paw Paw 10/17/2016 6:28am
10/17/2016 6:28am
You need to find out why you lost so much oil. The most likely leak point on that bike is the oil filter o ring not sealing.
The engine being starved for oil will generate excess heat and can cause it to stall. I would find the leak, fix it, check the other moving parts for damage including the cam journals. The cam journals are almost always the first part to show oil deliver issues and will score very easy. If they score, then you will also loose oil pressure and cause other issues.

Paw Paw
MicMcDude375 10/17/2016 7:18am
10/17/2016 7:18am
I did not think of the oil filter as being the leak point, but I will make sure to check that. My dad did see some black smoke coming out of the exhaust when I first started the bike at the track, so my suspicion is that it was burning oil off. Thanks for the tip Paw Paw.

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