It’s not a shim. It’s a steel-backed and babbit-plated.
Hi JB,
Yep and you'd remove material from the steel backing.
A cam shim is a an entirely different application and I wouldn't be altogether confident of being able to maintain parallelism in the home shop for such a small hardened item. Nevertheless, people do it and seemingly have little trouble. A cam shim is also subject to high point loads a thousand times every minute whereas a thrust washer bears a much lighter load and infrequently.
A motor engineer friend showed me how to make custom bronze thrust washers for a Lotus 912 engine where the thrust flange on the crank needed to be refaced (long story). The machining put the required thrust washer dimensions well out of range of any available stock items.
I asked him - what about the white metal facing? He said: If you like, put a series of divots on the face with a small drill for oil retention, but it'll be fine either way - and it was.
Ray was a well respected builder of drag engines among others and he showed me the Austin Healy 3000 he'd converted with an alloy OHC Ford cylinder head. This sort of engineering adventurism was his stock in trade. I just went along for the ride.
So, from my experience (and guidance from Ray) I reckon it's entirely viable to tackle a thrust washer thickness issue using common sense, a surface plate, a micrometer and a tube of engineer's blue.
But yeah, I like the idea of using the old “good" thrust washer if the clearance then fall within range.