Why Left Intake Valve on 05 KX250F?

I have a 2005 KX250F, that I put all new valves, springs, guides etc... in about 10 hours ago due to the left intake being zero'd out. The mechanic insisted that I didn't need to cut the seats. I think that may have been a big mistake, as my left intake is zero'd out again.

In searching forums to see if there is any way to get more run life out of these valves, I've noticed that almost every post on the 04-05 KX/RM 250f's valves, it's the left intake that tightens up. Is there some reason for this one valve taking all the abuse? If that's the problem, can I get away with only changing that one valve?

As mentioned above, I didn't have the seats cut with the first valve job. Is this a must do when replacing the valves?


Yes it is a must do when a valve has already zeroed. It amazes me about some guy's that work on these bikes.If this is the first time you had do do the valves on an 05 they lasted long enough.You can use steel valves for a little longer life but you still must have the seats cut no matter what.The stock Kawi valves seem to last a long time though.As to why the left one goes first there could be a few options.I have not researched this on the Kawi's so I'm just throwing some Ideas out there based of CRF's experience.One could be that the left valve gets hotter as it may be closer to the exhaust port,Honda's is the right one on the 250's and the left one on the 450's the other reason some guy's suggest is the degree of the cam load on such specific valve.

The L/H valve area of the head runs alot hotter oil temp than the R/H side this affects the valve life and the spring too.

This is why PC bikes have oil coolers....

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