Valve adjustment 2010 kx250f

Hondas4Life3
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4/7/2017 9:16am
So I think I know the answer... New valves. But I wanted second opinions on what could have caused this. Im working on a 2010 KX250f. The exhaust valves were .001 tighter than spec. One intake was dead on. The other intake however was completely stuck open. The bike had almost zero compression and it went from a 2.95mm shim to a 2.70mm shim to get it back to spec. It has a complete procircuit head with their cams, springs, etc.

Why would only one be .010 tight and the other stay perfectly in spec? That seems like a lot of adjustment to get back to spec.. The intakes are supposed to be at .004 -.006

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Acidreamer
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4/7/2017 9:45am
So it was in spec with the 2.95 shim and after one ride it went to 2.7? Was it in spec when the head was built? I think the history will give the answer on this one.


One valve out of 4 is wearing .01" then it leads me to believe something is faulty. Whether its the seat or whatever. Based on your post i would take it apart and break out the calipers.
nage0139
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Fantasy
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4/7/2017 10:50am
The valve seats are the things that wear, and as they wear the valve rides higher in the head thus closing up the gap spec. 0.001" out of spec isn't so bad, and a new shim would take care of it. 0.010" out of spec is not good and I would think you need a seat recut and possibly a new valve. Makes sense that it was stuck open and no compression if the seat and valve do not match.
Hondas4Life3
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4/7/2017 11:00am Edited Date/Time 4/7/2017 11:01am
Acidreamer wrote:
So it was in spec with the 2.95 shim and after one ride it went to 2.7? Was it in spec when the head was built...
So it was in spec with the 2.95 shim and after one ride it went to 2.7? Was it in spec when the head was built? I think the history will give the answer on this one.


One valve out of 4 is wearing .01" then it leads me to believe something is faulty. Whether its the seat or whatever. Based on your post i would take it apart and break out the calipers.
No it was 2.95mm and it took a 2.70mm shim to get to spec haven't ridden it since just fired it up on the stand .25mm is roughly .010
Paw Paw 271
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4/7/2017 12:20pm
Try cleaning the carb jets. It sounds like the pilot jet is clogged.
Which intake valve was the tightest?

Paw Paw

The Shop

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4/7/2017 1:54pm
It the valve Stuck it's a good possibility it's bent and could be giving you a false reading as the valve is tight in the guide.
Hondas4Life3
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4/7/2017 9:07pm Edited Date/Time 4/7/2017 11:19pm
Update Cleaned the pilot and main out and it runs good. It is kinda hard to start but that is expected from a bike with a worn out intake valve. Sometimes it starts in a few kicks sometimes it wont start after 30. The left intake (stator side) was the tight one. As stated the right intake was at middle of spec at .005 clearance. I will be checking the clearance again after this weekend if the intake closes the gap more than .002 over the race weekend we will probably take it apart. It has 80ish (according to hour meter) hours on it since the head was built.

If its not a result of common wear im thinking it may have dropped a guide slightly.
Paw Paw 271
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4/8/2017 5:23am
I would suggest that you try to run the valves at the widest part of the spec.

Paw Paw

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