If you were using a hardened cups under the springs and installing your shims under the cup, does the shim have to be hardened? I am having to shim over .200 so I was curious if I could sandwich a 1/2" flat washer under the cup and maybe sandwiched between two hardened shims so spring_cup_hardened shim_flat washer_hardened shim_head.

I would hand this job off to your local engine machine shop.

Do you need .200" or .500"? If it were me and I needed .200" shim under the springs, I'd be looking for another spring.

my OCD would not let me do that, I would be looking for a better spring choice. Birdtracker

Are you feeling really lucky
Anything rubbing against anything made of spring steel better be a s hard as the rubbing part is
I use a lot of valve spring shims when setting up heads for solid roller lifter motors, some are spring steel and some aren't I try and make sure the spring bottoms are sitting on a spring steel shim
Most of the .015 valve spring shims are black and made of spring steel

My old 906's were about 1.88 ish valve height, the RPM's I'm setting up are right at 2.0 valve height. In checking all my springs (Isky 8005a), they are averaging about 380 lbs/in instead of 400 so I need a little bump there. The cups are .060 so I am having to shim anywhere from .140 to .170 to get 150 lbs on the seat and get them to within .100 of coil bind. I did learn on my first valve spring set up, not to the put a thin shim under the spring, hardened or not, as it beat them to death. I now put my shims under the cups and let the springs sit in the cup. I was able to find grade 8 washers at TSC, which I think are hardened for less than $5. I took my caliper with me, and was able to get 16 that all measured .100. I will sit the washer on the head, then my shim, then my cup.

ake sure the springs are centering at either the top or bottoms so they can't walk around very much when revved up

Might want to consider the Flatness of those washers....

What kind of variation would be acceptable? I did catch myself rubbing them on some sandpaper on my granite top just to knock down any high spots on on the coating. I noticed when I was comparing the grade 3 stuff to the grade 8, there was a lot less variation in thickness and appearance. It wouldn't take long to check the run-out on them. Worse case scenario is I hit with a surface grinder.

I think the issue is that the valves want to rotate as they go up and down. Most valve spring shims have a up and a down side. The down side has small ridges to keep the shim from turning. I have taken a lot of cheaper shims off that were just hard steel, and you can see the wear marks where they spun on the head. A lot of stock engines especially truck engines have valve rotators so the valve spins freely, it helps keep carbon off the seats and promotes cooling of the valve. Got to remember valves have to cool with heat transfer to the seat and guide.

Are you saying .200" plus the locator? Sounds like the wrong spring/retainer/ lock for the aplication. Definately wouldn't use flat washers. -.100 retainers and -.050" locks would get you close.
Doug

The valve heights range from 1.965 to 1.9375, and I need an install height around 1.800 to get 150 on the seat, so I need around .190 to .220 of shim including the locator. I measure every spring to know exactly what height I need for each spring to hit 150, then I match my spring height to the valve height to limit the amount of shim for each valve. The grade 8 washers are hardened, and actually pretty flat, I measured several and got less than .0005 run out. I have cups with the ridges on the bottom and I have some that do not. I noticed the ones on the heads (aluminum) do not have the ridges and are smooth. I did search for a different spring one day, and I wasn't able to readily find a spring with 150 on the seat at 1.900 or so and still get within .100 of coil bind at around .560-.580 lift. Most of the ones I found where .150 or better on coil bind.