Just curious, have you tried using an expandable reamer on a BSA timing side bush? have you watched someone else try it? or are you speculating that it won't work?
nah im just speculating based on 40 years as a fitter and turner .........but way back in the dim distant past i did take one to an engine rebuilder ...he totally stuffed it up using an adjustable reamer ...exactly as Ray Elliott ha described above
he then proceeded to go round the open end of the bush and bash in some center punch marks to make it seem like an ok fit ......then when i inquired regarding the appropriateness of this "remedy " he said "oh well its only a motorbike" ....the id was chattered and oversize . What an expert , then he wondered why i wasnt so keen on paying him.......gee i dont know perhaps i was just being churlish
funny thing is this guy had a good reputation so he must (or his 1st year apprentice must have) been having a bad day
or 
