YZ450FV 2006 Valve Adjustment - What Size?

The center intake valve is WAY tight. It has a 191 shim. To keep from wasting money and drive/order time, what would be a good guess on a replacement? I'm willing to get two at a time. Would a 175 and a 165 be a good start? Read on for more detail:

I got through the Cam Chain replacement. Unfortunately, I did not read the last section of Greyracer's post about checking the Valve clearances BEFORE taking the caps off. I assumed since it was running great when I took it apart, that no valve adjustments would be needed. Anyhoo, the middle intake valve is tighter than a bull-dog bite. The other two and the two exhaust valves are all within specs. I can't even get an .002 (.05mm) in the middle intake valve. So I took the whole darn thing apart again and removed the valve cap/cover. Turns out to be a 191 shim in there form the factory (assuming I'm not reading it upside down). With the number centered at the bottom half of the shim, it's 191. Any help is appreciated. Bronco.

The center intake lobe is accessible through a fairly narrow gap in the head, and more than once I have seen people make this same claim and have it turn out that they weren't actually getting the feeler gauge down to where it could go between the cam and lifter at all. Take a closer look with a flashlight to see if the feeler is going to the right place.

Also, be certain the gauges are narrow enough to access the valve. Most are, but some need to be trimmed.

If the clearance you're measuring turns out to be accurate, and the bike still has good compression when cold, you might get by with a 180. But that still would mean trouble.

I'm definitely getting the feeler gauge in there. The valve moves up and down. Besides, it was running like a champ before I started this process (of changing the cam chain). I pretty sure that a 180 shim will not get it within spec, but I'd buy one and try it, depending on what you mean by "this still means trouble". Can you elaborate? Let's assume the 180 shim gets me to

.004. Am I good to go? If not or if the 180 won't do it, what will need to be done?

What I mean is that there is no way for the valve to have worn enough to need a shim 2 or more sizes (0.10mm or more) smaller than it was originally built with and not need to be replaced.

The one thing that might be going on here is if you had the buckets and shims off and didn't get the center one seated in the spring retainer completely. If it's turned up and cocked, it could account for the lack of clearance.

The lack of clearance was discovered before I took the bucket off. Would it have been running good had it been that far out of spec? I carefully torqued the intake and exhaust. All valves are within range except that one. Should I put in the 180 and if it is within specs am I good for re-assembly? If the 180 shim won't do it, do I have a bent valvue?

It could have run just fine if the clearance was greater than 0, yes. However, as I said, that's at least 0.09mm of clearance lost, which equates to .065mm of wear at the interface of the seat and valve face, and far more likely the valve than the seat. Since the coating on the valve face is not more than .01 thick in most cases, you can pretty much be certain it's gone.

You can reshim to clearance if you like, but you should recheck the clearance after your next ride to see if it stayed put, then again each ride after that for a while to be sure it's stable. If the coating is worn through, it will quickly loose clearance due to accelerated wear. If this condition exists, it can lead to the valve scrubbing and twisting as it seats, and that can lead to a valve braking off.

Bent valves increase clearances, wear the the valve face/seat reduces them.

I'll go with a 185 and see if it's within specs. If not, I'll replace the valve and go with the stock 191 for starters. Are the aftermarket "hotcams" shims OK to use?

Their shims are fine. So are the 9.48mm diameter shims from a 450 Honda, Kawasaki, or Suzuki.

Since you have it opened up, why not try a shim from another valve? All shims are interchangeable between valves, so find one (or more) that are smaller and go from there.

Just went from the stock 191 shim on the middle intake valve to a 185. It will take the .003 gauge, but the .004 just won't slide under. Really don't want to replace the one valve, but don't want a catasrophe either. Do you think I can go a while with it being tight by .001 in?

Run it that way for one ride and recheck the clearance. If it holds, take it for another ride and check it again. If it still holds check it after the next ride, too, and if it's still good, put a 180 under it and ride it for a while, checking it fairly often.

If, OTOH, it closes up right away in one or two rides, the hard coating on the valve is shot, and it needs replacement.

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