Post-adjustment valve issues?

RonKZ650 wrote: Shims don't wear, it makes no difference if the number is up or down on the under bucket shims. Of course on the over bucket keep the number side down, as the cams directly rub on the shim. Still makes no difference, just so the numbers don't wear. There are really only few possibles, either error in the original checks, error in subsequent checks or the rare possibility of a shim marked wrong. Unheard of back when all shims were factory, now that that the ever popular Chinese shims are the norm, a possibility.

Shims DO wear and on shim over applications become dished and thinner towards the middle within the arc of the camshaft contact area.
When shims are badly worn and still have the size marked on them even replacing a shim with the same sized unworn will close up the valve clearances.
Maybe this is the case if the correct procedure is being followed.
Unless i'm using new shims I always use a micrometer to double check the actual size of used ones. ( if they are significantly dished they get binned )
The micrometer check sometimes shows up slight fractional variations in thickness of like for like new shims of the same size.

We are talking about a 650 engine right? If so, the shims are under the buckets so doubt there is any shim wear in play here

Regarding the shims, there is thickness variation between similarly marked parts, and sometimes changing shims doesn't result in changing the valve clearance as much as one would think. For example, the original shim may be on the thin side of the tolerance range, and the replacement on the thick side, thus the net change may not be as much as you would think. As mentioned, measuring the shims, current shim and new shim, with a micrometer is a good method to make sure you are moving the adjustment as much as you think is necessary.

One wild card factor regarding valve adjustments relates to how you are checking the valves. IF the adjacent valve to the one you are checking is compressed, the valve spring will push up on the camshaft and skew it to one side of the journal clearance. On Suzuki GS engines you adjust adjacent valves in pairs for this reason. This is a fine detail of course, and it doesn't make all that much difference how you do it, just be sure to remain consistent each time you check because the checking method will result in different measurements.

Also, if the valve has very marginal clearance to begin with, there may be carbon build up on both the seat and valve so all bets are off as to how the clearance will change after that situation is corrected. In many cases you need to move the shim two sizes smaller that what's installed.

zed1015 wrote: . . . Shims DO wear and on shim over applications become dished and thinner towards the middle within the arc of the camshaft contact area. . . .

The original poster is dealing with a KZ650 (shim under bucket design).

Am wondering what causes an under-bucket shim to wear?

And whether the under-bucket shims have the special "hardened surface" as do the over-bucket shims?

Good Fortune!

zed1015 wrote: .......Shims DO wear and on shim over applications become dished and thinner towards the middle within the arc of the camshaft contact area.........

This may very well be true for shim over bucket engines, but please explain what would cause wear on a shim that sits under the bucket. I believe RonKZ650 is correct, and he has more KZ650 miles than anyone I know - probably more than anyone on Earth, to back up his assertion. The cams never contact the shims in question, and I find it hard to envision that a hardened shim would be hammered out of spec by riding between the valve and bucket because there's no air gap on either side of the shim to permit hammering. Ed.

I have always used shim under bucket in all my KZ1000 motors. I have plenty of 13mm shims with noticeable wear on the shim where the tip of the valve rides on the shim. My motors were used for high speed backroad riding and road racing. Break motor in on the street, then road race it next weekend. I shifted at 10,500 to 11,000 RPM on a Factory Kawasaki road race tach. I don't know if they will show any wear just putting around town, but run them hard and they will show some wear. I ALWAYS used nothing but real Kawasaki shims too, except for my half size shims.

Patton wrote:

zed1015 wrote: . . . Shims DO wear and on shim over applications become dished and thinner towards the middle within the arc of the camshaft contact area. . . .

The original poster is dealing with a KZ650 (shim under bucket design).

Am wondering what causes an under-bucket shim to wear?

On old jaguar's, the head of the valve stem would wear a hole into the shim over time. You could flip the shim over and run it for a while before throwing away. The steel they used was not as hard as modern shims.

That's because it was British. On my old Austin Healey 3000 I had holes wear in the rocker panels, gas tank, frame ...oh wait, that was just rust. :laugh: :laugh: :laugh: Ed

WABBMW wrote: I am wondering how you determined what the shim thickness is for those shims that needed replacing. Did you use markings on the shims? Or did you measure the thickness with a micrometer? I have seen shims with the numbers so faint that the numbers were hard to read. Possibly mistaken a 3 for an 8, or some such thing? I have also seen shims with no numbers at all, so manual measurement was necessary.

One final thought, although unlikely... Is it possible that a previous owner ground some shims down thinner, on the opposite side from the numbers, so that the actual thickness is less than what is marked? This is a bad practice since the hard coating might have been ground through, but it would explain why the clearance was reduced after those shims were replaced with ones that were truly the thickness that is marked. You might measure a few of them to see if they are the thickness that is marked. Just a wild thought.

Use Micrometers....every shim...every time. Always favor the loose spec for lash adjustment.

I run into all sorts of strange things with these old heads. When one comes in for work, I measure every bucket's thickness when setting up a valve job. Here's why. The thickness of the buckets is written on the top. Look at the variance....They got scrapped and new APE buckets installed. 7 of them were aftermarket and one was OEM....




If, for some reason, you have buckets that vary in thickness like that and if you have stock cams with OEM valve springs I'll give you a set of OEM buckets...if you need them. Just holler if you do.

Using micrometers is the safest way for sure, but look at the wear thing logically. The shim contacts the valve stem and also the bucket which the contact area is a smallish round nub, so both contact area are not that much different, so whether the shim is number side up, or down has little if any consequences. Over time it is possible the number wears off the shim, then using a micrometer to measure is the only way to get the size, but what I am trying to say is if the number is still legible, the shim can't be possibly worn because the number will always wear off first, it has to.

Dang -- I didn't expect this thread to get this much attention! I appreciate all your responses and suggestions.

The only reason I brought up wear in the first place is because I noticed the area in the center of each shim was discolored from where it contacts the valve stem. This made some of the numbers hard to read, and/or parts of the number were unreadable. Thankfully the numbers weren't generally printed straight across the center, so I was able to figure them out (I think) without too much trouble. So, I figured if the shim is concave on one side, flipping that around might cause the thickness to increase a little since a flat side would be seated on the valve stem rather than a slight indentation. Just a wild-ass guess, anyway.

Unfortunately I don't see much of a way around pulling the camshafts out again and digging back in at this point. Even more unfortunate is that I won't have time to take a look at it again very soon, as I'm headed out of town (cutting into my project time, arg!). Sounds like I should also invest in a micrometer. Any suggestions as to an affordable-yet-decent one out there?

steell wrote:

sbc1320 wrote:

serfrock wrote: Thanks again, guys. Unfortunately, regardless of any math I did, adjusting my shims seems to have had the opposite effect of what they should have.

It occurs to me that I re-used many of my shims, and I may not have been careful about what side was up -- is it possible that the shims were so worn that putting them back in upside-down caused my valve clearance to decrease overall?

Numbered side always goes down. If it's worn very much I chunk them in the trash.

If the shim is worn enough to trash it, then you probably ought to look for new cams also, I think they are both about the same hardness, so the cam is probably worn also.

Way back when, Chevy let a bunch of non hardened cams get installed in their 350's, cams didn't last very long as the lobes were worn off the cams.

Agreed. I can't see a cupped OEM shim happening with the lobe untouched. It just doesn't work like that. OEM shims are hard, hard hard. So hard they they can and do fracture into pieces in Shim Under Bucket setups sometimes.

serfrock wrote: Dang -- I didn't expect this thread to get this much attention! I appreciate all your responses and suggestions.

The only reason I brought up wear in the first place is because I noticed the area in the center of each shim was discolored from where it contacts the valve stem. This made some of the numbers hard to read, and/or parts of the number were unreadable. Thankfully the numbers weren't generally printed straight across the center, so I was able to figure them out (I think) without too much trouble. So, I figured if the shim is concave on one side, flipping that around might cause the thickness to increase a little since a flat side would be seated on the valve stem rather than a slight indentation. Just a wild-ass guess, anyway.

Unfortunately I don't see much of a way around pulling the camshafts out again and digging back in at this point. Even more unfortunate is that I won't have time to take a look at it again very soon, as I'm headed out of town (cutting into my project time, arg!). Sounds like I should also invest in a micrometer. Any suggestions as to an affordable-yet-decent one out there?

Sears, Harbor Freight, Grainger.....might even have them at the local auto parts store.