There are no oversize M20 guides that I'm aware of...They've made them for years for alloy head Triumph twins which are known for rattling them loose over time...I think they do them for A10s these days as well....
The first question is were your guides NOS or after market?...The original guides are actually tapered (theoretically)...When new they should measure .624"- .626" at one end and .625"-.627" at the other end ....
However if you look at those tolerances they could be .625" or .626" at both ends!!...Anyway, ideally they should measure up within that range somewhere...Ian
I tried to fit a new guide to a customers bike he supplied it hepolite stamped on it always measure first it was a standard guide but was 8 thou oversize he got it from a well respected bike shop i sent him to another who specialise in BSA on the phone yes correct gave him a measure turned out the same so if you want an oversize guide go and measure
