2009 KX250F Intake Valves Hitting Piston

anthonynoah57
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anthonynoah57
I bought a 2009 KX250F that needed a top end rebuild so I put in a Vertex stock bore 13.9:1 compression piston and a Cylinder Works stock bore cylinder. After assembling everything I discovered that the intake valves are hitting the top of the piston and wont allow the motor to turn.. I've triple checked the timing and it is dead on.

Any help would be much appreciated. Thanks.
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Paul_Pitzonka
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Paul_Pitzonka 5/10/2020 5:54pm
5/10/2020 5:54pm
If the timing marks are on I would suggest a Possible spun Cam Gear... Stock cam and valves? also is the piston in the correct direction (not doubting your abilities just eliminating possibilities)...
walent215
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walent215 5/10/2020 7:08pm
5/10/2020 7:08pm
Paul_Pitzonka wrote:
If the timing marks are on I would suggest a Possible spun Cam Gear... Stock cam and valves? also is the piston in the correct direction...
If the timing marks are on I would suggest a Possible spun Cam Gear... Stock cam and valves? also is the piston in the correct direction (not doubting your abilities just eliminating possibilities)...
This^^^ piston in backwards is most likely the culprit
kb228
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kb228 5/11/2020 3:13am
5/11/2020 3:13am
Id double check the timing mark you used. Theres 3 marks on the flywheel that you can possibly use. It caused confusion for me in the past on that bike.

Backwards piston is also a good suggestion.
ginjahhh125
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ginjahhh125 5/11/2020 10:01am
5/11/2020 10:01am
Check the clearance on your gaskets, had this same problem with a 350 warrior. Must’ve sent me the wrong ones or something but I ordered a new set and fixed my problem. Also make sure your valves are seated good

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anthonynoah57
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anthonynoah57 5/18/2020 6:06pm
5/18/2020 6:06pm
kb228 wrote:
Id double check the timing mark you used. Theres 3 marks on the flywheel that you can possibly use. It caused confusion for me in the...
Id double check the timing mark you used. Theres 3 marks on the flywheel that you can possibly use. It caused confusion for me in the past on that bike.

Backwards piston is also a good suggestion.
Ding ding ding we have a winner.. I had the timing all wrong. Thanks! Now onto my next problem.. everything’s back together and the motors spinning around just fine but I can’t get it to start. I’ve tried bumping starting it real good a few times and it wants to run but falls on its face and dies out. I’m thinking valve clearance. Any input? Thanks again
Paw Paw
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Paw Paw 5/18/2020 7:28pm
5/18/2020 7:28pm
Have you checked the valve clearances?
If so, what were they?
Have you cleaned the carb?
Do you have fresh gas in he bike?

Paw Paw
weland28
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weland28 5/18/2020 7:32pm
5/18/2020 7:32pm
Bike run good before? And yea valve clearance would be first thing I’d check, as if you set it with it out of time, it could be way off. Also when the piston was hitting the valves you were being gentle right? If you hit it hard it could have easily bent a valve and one could not be seating right.

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