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07 KX250f valves and engine problems

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I took my 07 kx250f out the other day and made it 2 laps around the track before it lost all power and it just quit running. After that it was hard to start and had a little milky oil coming out of the crank vent tube, so I thought it was the head gaskets. Took it all apart and apparently the intake valves had been hitting the piston also. I then checked the valves over and everything was in spec. Then put a new piston and gaskets in it and it is still hard to kick, hard to start, and I believe the valves are still barely hitting the top of the piston. I do not know what to do next, maybe timing or bad bottom end? Any help would be appreciated, thanks.

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My 07 KX250F was hard to start when kicking it....it got to the point were I had to push start it just to get it running.....Pulled the head off and pulled all the valves out....Well come to find out one of the exhaust valve was so worn out it would not seat up so it would never build enough compression to run. The valves were in spec but there was no way of knowing without taking them out. I replaced all of the valves with Kibblewhite valves......and it runs perfect....most of the time starts on the first or second kick. Valves do wear out.....this is something I would check out....good luck..

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I took my 07 kx250f out the other day and made it 2 laps around the track before it lost all power and it just quit running. After that it was hard to start and had a little milky oil coming out of the crank vent tube, so I thought it was the head gaskets. Took it all apart and apparently the intake valves had been hitting the piston also. I then checked the valves over and everything was in spec. Then put a new piston and gaskets in it and it is still hard to kick, hard to start, and I believe the valves are still barely hitting the top of the piston. I do not know what to do next, maybe timing or bad bottom end? Any help would be appreciated, thanks.

Check the cam chain timing.

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You might check out Dave at MXTime.com, he reworks heads and valves up near Chicago. I had a cam chain jump and the valves hit the piston. I had the head reworked with new valves, new cam chain, piston and rings. When you remove the cam chain tensioner, pay attention to how far it is extended. If it is most of the way out, then your cam chain should be replaced ($40), cheap investment. Good Luck.

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I will take a look at the cam chain and the timing first. If its not that then I will take a look at the valves but I don't think they should be in bad shape, the engine only has about 40 hours on it and I always keep my valves within spec. Thanks for the advice.

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Where abouts in illinois? If Chicago. You can make the ~hr drive to my house. I'll look at it.

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Im down in Urbana. I may be willing to make the drive and I am probably going to be going up to redbud here in about 3 weeks or so. U a mechanic? If so what would you charge to look at it, im a little on the broke side.

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I am not a certified mechanic nor am I shop.

I just am good with these bikes. I can help you do basic diagonosis. I don't have the time for a full engine dissasembly and rebuild. How ever if it's something minor I should be able to diagnois the issue. Plus I have an 07 for parts swaping to further test.

If you want some feed back about me just ask.

As far as charging I general just require a case of pepsi maybe 20 bucks.

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Thanks for the offer and I could definately afford a case of pepsi...haha, but I think I figured it out. I took it back apart and found that the timing was off. The cam chain tensioner didnt take all the slack out of the chain so it jumped a tooth. I fixed it for now to see if that was the problem and sure enough it started first kick. Next step is to replace the cam chain. Do you have to split the cases to do this? I am assuming you do but not for sure.

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perhaps your cam sprockets slipped and moved out of adjustment. since their only pressed on. i give my intake cam a little weld to make sure no slip. to replace the cam chain you might be able to put a new one on by removing the head and cylinder and then taking the ignition cover off as well as the flywheel and feeding the new chain upward from the bottom. i cant remember if i did it that way or did it as the cases were split. either way its possible. might need to wind the chain up pretty small but i have faith it will work out. i got a cam chain on ebay for like 20 bucks.

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do not need to slit the cases. you need to pull the flywheel off though.

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Alright I will try that out, thanks. I got it running for now and it runs really good but when the engine comes down to idle and starts idleing, it sounds like the chain is slapping the case or something. Im assuming its cause the chain has too much slack. Hopefully once that is back together and fixed all will be well. Thanks for all the advice.

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Don't waste any time getting that chain replaced, if it is loose and has jumped before it is more than likely going to happen again. The next time it could wreck your valves, head and piston. All you need to change the chain is to remove the valve cover, the left stator cover, remove the flywheel, install new chain and put it back together.

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The very LEAST to do is to change both the chain and the tensioner assembly.

It will save you lots of cash in the long run.

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i have a spare cam chain tensioner in the garage if that helps you out. its missing the 12mm hex bolt on the end where you slip the spring though. but you can use the one from yours! i have a cam chain ill give you too. mind that its the one that was on my bike before i took it apart but it never jumped timing and it looks to be in phenomenal shape. i just replaced the chain while i was doing the rebuild. let me know if you want them

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