Just done valve clearances on bike I'm about to start building 1 shim is missing(not in engine I nicked it for my bike) heats best way to sort the clearance on the 1 valve do I just put any old shim in it? And calculate from there what I need?

Yes.

Put any shim in there you have and measure it up

The only problem will be if the shim is too big you will need to use a smaller one so you have a gap to measure., should be easy to calculate what size you need from there

Thanks for fast reply will get it done