Valve Adjustment 450 XC RFS

610 Views 7 Replies 4 Participants Last post by YenkoS/C, 1 mo ago

YenkoS/C

Discussion Starter · 2 mo ago

So I just did a valve adjustment on my bike. First time the valves have been touched and the motor has 50 hours on it. KTM spec for clearance is .039" to .059" and everyone seems to recommend adjusting the valves at .050". My exhaust valves were right at .050". But my intake valves were tight and I could not get my smallest feeler gauge of .020" between the rocker and valve spring. So I had to adjust the intake valves to .050". I thought these valves wear loose? As in they get more play in them as they wear and dont get tighter as they wear. Am I wrong?

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steveo525

· #2 · 2 mo ago

Intakes were always tight when I did mine. Can’t tell you why, but that is the case. I attribute it to Austrian/German engineering on the KTM’s.

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quad97

· #3 · 2 mo ago

The RFS engines are notorious for having soft intake valves even in the dirt bike variations. The surface that seats against the seat in the head wears and the valves pull up deeper into the head. Just something that has to be adjusted for over time.

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YenkoS/C

Discussion Starter · #4 · 2 mo ago

If I had to estimate the amount of adjustment needed I would say .040" to get it within spec. Anyone know how much adjustment can be done over time before a head rebuild is needed? Like a max amount of adjustment over time?

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quad97

· #5 · 2 mo ago

I think you're missing a zero in your clearances. 0.040" is a lot, and the clearances you're looking for are 0.0039" and 0.0059". If you really had to go 0.040" to get clearance then I would say there is a major problem about to come apart.

Frequency of clearance adjustments will tell you if it's going downhill. Like if you have to adjust by a few thousandths, then again in less than 10 hrs it's getting bad and needs a rebuild with new valves. If it's only every 50hrs by a couple thousandths keep going.