Has anyone here ever shimmed a frame / seat post to make up a difference of less than 0.2 mm? I've got a bit of a weird case, which I suspect is a frame that was not reamed properly and the main seat tube is 26.8, but the upper 25 cm is about 26.9. When fully tightened, the seat clamp tabs touch each other but the post still slips. A coke can shim that goes abut 25 mm down, and a third of the way around the post circumference seems to have done the trick, but I wonder if it's safe to put a shim around only part of the seat post? Any ideas.
It's a Raleigh M Trax Duo Tech from 1995, with the bonded steel and Ti frame. What's a bit odd is these frames (I'm a bit of a collector of them) universally have 27.0 seat posts, and this is the first and only one I have ever heard about with a different diameter. I started to wonder whether it came from the factory incorrectly reamed out, but I'm doubtful Raleigh Special Products would have allowed that to slop through, and in any case the frame has had plenty of use judging by the marks to the finish, so it must have had a correctly fitting seat post at some point in its life.