Thinnest allowable valve shim?

[KicknAsphlt]

Hey guys, finally getting some more work done on the car, and the current task is valve lash. Did my initial clearance checks yesterday, calculated the new shims from the spreadsheet and got the proper sizes installed today. On my post-swap clearance check today, most numbers are right in the middle (or close), with only a few that are on the edge one way or another. My only real issue is I have one lobe that is more or less zero-clearance. My thinnest feeler gauge is .04mm, and that won't go through; I think I saw the slightest amount of daylight, but I'm considering it zero-clearance.

According to the spreadsheet, that one needs to go from the 2.58mm shim that's in there, down to a 2.33mm shim. I know you can order them that thin from other places, but since the TSRM says 2.50mm is the thinnest you can order (from toyota), I was wondering what is the thinnest shim allowable in the bucket?

Here are my current numbers from front to rear of the motor (in mm):

Exh. -- .20 | .23 | .20 | .23 | .28 | .25 | .28 | .30 | .23 | .25 | .00 | .18
Shim Thickness
Old -- 2.93|2.68|2.74|2.75|2.74|2.84|2.88|2.85|2.59|2.88|2.58|2.70
New -- 2.88|2.66|2.69|2.73|2.77|2.84|2.91|2.90|2.57|2.88|2.33|2.63

Int. -- .20 | .20 | .18 | .25 | .08 | .20 | .25 | .20 | .20 | .20 | .15 | .20
Shim Thickness
Old -- 2.61|2.69|2.80|2.77|2.62|2.78|2.85|2.80|2.85|2.84|2.82|2.60
New -- 2.61|2.69|2.78|2.82|2.50|2.78|2.90|2.80|2.85|2.84|2.77|2.60


And here's what I started with:

Exh: -- .20 | .15 | .18 | .23 | .25 | .15 | .28 | .23 | .00 | .23 | .00 | .00
Shim Thickness
Old -- 2.98|2.78|2.81|2.77|2.74|2.94|2.85|2.87|2.84|2.90|2.83|2.95
New -- 2.93|2.68|2.74|2.75|2.74|2.84|2.88|2.85|2.59|2.88|2.58|2.70

Int. -- .00 | .10 | .18 | .35 | .00 | .18 | .30 | .00 | .20 | .23 | .18 | .00
Shim Thickness
Old -- 2.81|2.79|2.82|2.62|2.82|2.80|2.75|3.00|2.85|2.81|2.84|2.80
New -- 2.61|2.69|2.80|2.77|2.62|2.78|2.85|2.80|2.85|2.84|2.82|2.60


Two things about this... First, I'm measuring the shims with a digital caliper from Harbor Freight...not sure how accurate it is, even with zeroing the caliper between measurements, sometimes it'll read (for example) 2.79 one reading, then I'll come back later and it'll measure 2.77 or 2.81. Also, the readout will fluctuate, even on a fresh zero-out...sometimes it'll read -0 or -1, and sometimes it's just plain 0 or 1.

Second, I read in some other posts that valve jobs can affect lash clearances. With that in mind, the head I got was from a member on here who grenaded the #6 and the head was scarred. I had a local guy repair the head, but I think that included some bowl and valve work to do the repair.

With all that in mind, I'm open to hearing suggestions about this situation, as well as a possible definitive answer to my original question in the title - how thin can we go with the shims? Do we have to stick with the TSRM-given 2.50mm, or can we go thinner? If not, what do I do about the clearance on the #6A exhaust valve? Thanks in advance guys!

 

[GrimJack]

I've known many folks to have shims cut down to much thinner than the 2.5mm - never heard about any problems, whether that's because the engines popped due to other reasons tho, well, who knows. I don't think I'd be too concerned with shaving one by enough to work there.

Also, has this head been run since the valve job? If it's new, chances are the clearances will tighten up a bit more as the valves seat.

 

[KicknAsphlt]

No, head hasn't been on a running motor since the repair/rebuild. I was planning on getting the lash set to about middle of the road, then checking it again sometime within the break-in period, probably after about 500mi. I did get the shims today at a local bike performance place, and the guy told me to come back if I needed anymore...basically said he doesn't use 'em anymore and I could more or less help myself, so I think I'll stop by tomorrow and see if he's got something that thin. My only concern is if the shim is too thin, then it might sit below the lip of the bucket, which is what I'm trying to determine - at what point does that happen.

 

[Enraged]

2.30: http://www.cylinderheadsupply.com/kl9514-1.html
2.35: http://www.cylinderheadsupply.com/kl9514-2.html

 

[GrimJack]

That's pretty simple to check, too - measure the lip on your bucket. It's a fair bit less than 2.5mm, that's for sure.