while tinkering/fettling after all these years of owning the bike I've finally noticed this, just shows I've never used cam chain adjuster! probably seized anyway! it would appear previous owner/owners has carried out some sort of "mod" it uses an Allen bolt for the adjuster bolt and would appear to have a sort of pin drilled though - perhaps to lock it. I work on the principle of if it ain't broke don't fix it but any ideas? Bike runs fine as is by the way.