Valve shim/pad stuck.

Hello, I attempted to adjust my valves on my 2000 YZ426F, after installing the pads that the service manual recommends they are still tight. I should also mention that the previous owner installed a Zip Ty 12oz. flywheel weight which covers the timing marks, so I called Zip Ty and they told me to look through the spark plug hole to find TDC. I did that and also lined up the dimples on the cam gears with the top of the head, is that accurate enough to check valve clearances? Clearances per manual should be .15-.20mm intake and .25-.30mm exhaust.



.05mm 186 changed to 176 (shop did not have 175)

.05mm 182 changed to 170

.05mm 182 changed to 170


.09mm 182 changed to 160

.09mm 184 changed to 165

After installing new shims and putting motor back together they now read:








Is it normal for the service manual recommended shims to not fix the problem? When checking the clearances should you have to push the gauge hard to get it under the cam or should it go under easy? So I took the top end apart again to check to see if the shims were seated properly and now one of my exhaust shims is stuck in it's hole, how do I remove it? I've tried strong magnets, a razor blade, screwdriver and it won't budge. Sorry for the long post, any help would be greatly appreciated.


First of all, welcome to TT. This is exactly the sort of thing TT is good for.

I would suspect you may not have the piston at TDC. This could have happed either when you took your "before" measurements or when you took your "after" measurements. Especially since you have to use an alternate method of finding TDC. Judging by your "before" measurements, it looks like you picked the right shims and your valves should be in spec with the new shims in. Another possibility is you did finde TDC, but the new shims have not seated completely in which case your measurements would still be on the tight side. Maybe try turning over the bike by hand a few times to see if that helps the shims seat.

With the feeler gauge, it is difficult to "tell" someone how it should feel. There should be some reistance to pulling the guage out, but not so much that you have to tug on it and not so little that it takes not effort. I think it's about like pulling a piece of paper out from under a big phone book or dictionary. Maybe someone has a better way to describe it, but that's about how I think it should feel.

As far as getting a stuck shim out, I had the same problem a couple times. I finally got them out by tapping on the exposed edge of the shim with a screwdriver and hammer. Try to get as much of an upward angle on the screw driver as possible and just keep tapping. Also try to get at the edge of the shim from multiple sides so you can "rock" it back and forth to loosen it if that makes sense. Both of mine eventually came loose doing this. Just be carefull not to hit the wrong thing with your screwdriver.

Good luck.

I think I might need to remove the flywheel weight to expose the timing marks, that way I am sure that I'm at TDC. I will give the stuck shim trick a try and see how it goes. If anyone is wondering why the "NevadaCR500" name it's because I used to be "Nevada426" but forgot my password, I also own an 2001 CR500 so I decided to use that name.


Thanks for the tip I managed to remove the stuck shim, I have the drill down now. I Had my wife stick a screwdriver down through the sparkplug hole and help me find TDC, and I marked my flywheel weight with a sharpie marker. I then took new measurements and got new smaller shims, installed everything this morning and my intake clearances are a little better but my exhaust is still WAY out of spec. I can't figure out how this is possible, I'm following motoman393's directions as well as I have a service manual. It seems so simple but I just can't seem to get within spec. I was wondering if valves can only be adjusted so many times then they have to be replaced because you cannot achieve proper clearance anymore, I have no idea how many times they have been adjusted because I baught the bike used. Do you need special feeler guages? Mine are Snap-On metric (I think) about 3" long blades. I found this on DirtRider.Net "anytime your shims start dipping below 170 on the stock valves you are heading for trouble." All of my shims are below 170 does that mean my bike needs new valves?


another way to get a stuck shim out is compress the valve spring a little with the shim bucket off.

Nevada, I'm sure you know this, but a 4 stroke can be @TDC with a set of valves open. This means no clearence. You have to be on the compression stroke. Make sure the cam lobes are opposite one another.

I feel really stupid, I discovered what has been causing all of my heart ache. My feeler guages are not metric they are STANDARD:cry: . I bought a used set of gauges at the pawn shop that had numbers 1 2 3...all the way to 25 I thought that that was .01mm .02mm.... .25mm but it was not, last night I decided to measure with my dial caliper and noticed that those numbers are thousandths of an inch not metric. I purchased a set of metric from sears and walla, now my clearances are like .40mm on intake (I guess my valves were perfect or pretty close from the get go). Now I have to start all over but at least it should work this time, I've had this motor apart 4 times in the past 3 days for nothing all because of not using the correct guages.


I remove the shims by cleaning them first and sticking a piece of tape to them. They then lift right out.

Make sure you put the buckets back in their original locations. They can be different thicknesses and are color coded with a dot of paint underneath. If you had a tight valve and ordered the proper shim but installed a thicker bucket you'd still be tight.

I have it all worked out, I purchased a set of metric feeler gauges and adjusted my valves to the correct spec (turns out only one exhaust valve was tight by .02mm). I only change one shim at a time that way I do not mix up the buckets. So basically I spent a week of afternoons and about $100 getting a good education. By the way what do the colors mean?


I'm guessing that the shims are mass produced to certain tolerances and then measured and colored according to their actual thickness. I had green and orange. I checked them with a micrometer and the oranges were a couple of thou thicker than the greens. Connecting rods on 4 cyl street bikes are also color coded but it is for weight. Each color has a weight range of a couple of grams or something, I forget the exact weights. It doesn't matter what color rods are in your engine as long as they are all the same color for balance. Again, it's probably easier to produce a bunch and then group them than it is to get every one to an exact weight.

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