CRF 450 Valve Job Notes

Had an intake valve going bad on an '02. Upon removal the valve itself was clearly wearing and the seat was not worn. Replaced both intakes and of note was that the intakes clearly have less spring tension than the exhaust valves. Maybe the new springs (on the intakes) were more resilient but I've seen references to the installed spring length being suspect in the valve wear issue.

In any event, all I did was drop in new valves and springs and the clearance came out a perfect .006" each side.

isnt the clearance supposed to be .016?


isnt the clearance supposed to be .016?

You are correct if you are using metric measurements.


Actually it's 0.006-/+0.001 in.

Actually it's 0.006-/+0.001 in.

Right on man, I was ready to help that cat out as well.

.005"~.007" on intake

.010"~.012" on exhaust

I think the soft spring would hurt the valve , if you ride it on the rev limiter. The softer spring would float sooner and beat the valve up more.

I think the soft spring would hurt the valve , if you ride it on the rev limiter. The softer spring would float sooner and beat the valve up more.

The intake springs do have less tension. They are designed that way from the factory. Not an issue. Now he may have removed carbon deposits when he had the head off and that would equate to the recovered valve clearance.

My 02 crf 450 was losing compression, so I filled the cylinder with air and could hear it leaking out of the intake and exhaust and into the block so I just cut my valves and head. Will I have to shim it different or buy new springs? It alos has a hot cam in it so does it need stiffer sprigns for that cam? The thicker shims are for the intake side right? I just wanna double check b4 I put this all back together. How do I know the valves are adjusted right? Thanks

The springs are so weak to start with that even brand new OEM springs are just barely stiff enough.

Its my suggestion that you always change the springs. In an ideal world, Id change the springs every 10-15 hours if I was saddled with the OEM springs and valves. You'll get more life out of the valves with a proper valve job, good after market springs like the ones RHC has made and a good quality valve and closing the lash up to .004 on the intakes an .006" on the exhausts.

And so everybody understands, even the slightest bit of carbon left some how hanging onto the intake or exhaust seat would allow the valve to burn in almost no time at all.

Clearing carbon out of the CC wouldnt change the valve lash at all, or could it have any affect or effect regarding the valve lash. The lash closing up is a function of valve face wear caused by an excessively hard seat and a sub-standard coating on the OEM valves failing and exposing the Ti to the hard seat. The Ti uncoated wont stand up to the seats, the valve face cups out, the lash goes away and its time for a valve job. Its that simple.

I just finished putting in new steel valves and springs(not oem) and now all of my valve clearances are way out of wack. I just re shimmed because I installed a hot cam stage 1 a month ago and i have only about 3 hrs on the engine since. Why are the clearances so out? Any knowledge would be awesome!

Hey I dont mean to get off topic but I dont know how to post and was wondering if any one had a tip for removing the cam sprocket bolts?

I just got done doing my valves on both my bikes so I had the cam off and on about 10 times to get the shims right. Anyway, this may not be the correct method but it worked for me. Just brace your allen up againt the engine mount and loosen making sure to keep hard flat pressure against the bolt. Loosen it only a little bit and then advance the piston with the kick lever and do the other bolt, take that one all the way out, sping the sprocket again, connect a wire to the sprocket and chain to keep the teeth lined up, remove the second bolt and proceed taking off the cam. Make sure you use some thread lock when putting them back on. Have someone help you and use the kick start as leverage agaisnt the cam to tighten.

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