Okay, so you need to thin down your shimsit’s not too hard, but it’s a skoshy bit time consuming to do it correctly.
The first thing you’re going to need is a grinder to which you can attach a mildly abrasive disc. I had the best luck using the Walter Quick-Step polishing system, which is available from most welding supply houses.
Anyway, take the shim that is closest to the value you need, and take one of the shim holders. This means that you’ll either have to pull the cam box, or take the cam shaft outor you have a shim holder laying around.
Using a micrometer measure at least 7 points around the shim, focusing on the central portion which is actuated by the cam. You don’t have to write these down, per se, but note the general thickness and pattern.
Place the shim upside down in the holder and do the majority of your work on that sidethe top side will be moulded by the cam.
Using the blue disc provided with the Walter Quick-Step system, which is roughly equivalent to the 3M abrasive disc that is dark red (not too coarse, not too fine), begin to grind the shim at a very shallow angle, 10-15 degrees or so, using the edge of the grinder. By applying enough pressure at this angle, you will flatten the griner edge ever so slightly, and it will cut evenly across the shim. Also, continuously rotate the shim against the edge of the grinder, and move it back and forth–you do not want it to come to rest against the grinder.
Keep the shim holder in your bare hand, and continue to grind until you can’t take the temperature any more.
Rinse the shim under lukewarm water until it is cool to the touch, and take measurements again. This time, just take a bunch of them. You want to find out if you’ve been favoring a place to grind. If so, avoid that area once you start grinding again.
If you’re like me, you weren’t able to hold the shim holder until you’ve ground off about .03mm–so it can go pretty quickly. The reason to take a break every time it gets hot is to make sure you don’t grind too much off.
Repeat the cycle of grinding, getting burned, and measuring until you are within 1 or 2 cycles of completion. At this point, you need to be much more careful, and reduce the time of your cycle. Take more measurements, and try to keep everything very even.
That should be it. The Walter Quick Step kit is actually very useful aside from grinding shims, and I recommend it to anyone that is relatively anal about polishing stuff.