Groily thanks, that's very useful info. I may be looking at converting a BTH from auto to manual. (It's for a single), I have a manual end casing, and I wondered if the auto camring would work, as long as the correct slots were ground in for the 'limiting peg', cable connector etc.
It should be OK Jools, by extending the one cut and making the other for the advance and retard (if one is not already there - it might be, can't recall off-hand and don't have any manual ones to look at at the moment).
BTH are a bit different from Lucas. You'll see what I mean when you look, but the AR 'notch' doesn't go right through the ring, it's a groove more like. As ever, arguably a fraction more elegant than the Lucas, with a nicer action on the plunger and associated parts and a much tougher end housing.
The fine tuning peg on the BTH (usually on the left hand side looking points end on) is a complete PITA to get out sometimes - there was a special tool with an offset pin to do it, but the plug is usually peened, is tight as a drum, and a tool I made wore out pretty darn fast for not being a proper hardened thingummy. Ouch!
The critical thing when modding is to be quite certain you elongate the main notch in the right direction! Sounds obvious, but it's a bit like patting your head and rubbing your belly at the same time and mistakes get made - don't ask how I know! The points need to open, in the fully advanced position, JUST after the flip point of the armature going in the right direction . . . . Delay causes weakening of the spark, opening before the flip will guarantee no spark. I always play with the camring position with the cb assy fitted before modding to establish the best position, then mark it indelibly where I want the notching to be.
