I was thinking about your vibration issue with the 2 stroke. I have tried, with some success, to tailor fit the bolt/hole relationship. Having the bolt fit perfectly snug in the hole has helped stop the bolt from loosening.
If you have the right sized reamer can you find a bolt slightly larger, then fit it with the reamer. Anyway, it worked on my old Triumph (not Henkley). The particular frequency of the vibration will have its own type of problem. That is to say; what works at one frequency may not work for another.
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