Lucas called the later steel backplate assembly "low inertia". Low cost more like. Don't know about the inertia either, as the force required to open the steel ones can be considerable even if the weight of the rotating mass is less than the earlier type. The advantage is they work for anti-clock and clockwise mags by fitting the moving point one way round or t'other - provided the fixed contact point is on the correct side. Original ones, some of, had a fixed point on BOTH sides of the butterfly, but most sets are anti-clockwise rotation only, with just a rivet (one of the bits that broke on Wilko's) where there could be a second contact for a clockwise mag like on a Vincent, Douglas, loads of cars etc. And that's a fiddly mod too - swapping a rivet for a decent tungsten point in a very confined space. Been there, done that and didn't like.
The worst of the later sets, in my view, is that the opening point is low tension 'live'. So if the spring blade, or the 6BA screw that retains it, kisses the camring on the way round, bye-bye sparks. The brass sets were arranged the other way, so there couldn't be a low tension short circuit (for that reason at any rate).
If the adjustable plate is bent, it might be because the insulator - a small figure of eight-like bit of nylon, usually white-ish, wasn't seated properly. Easy enough to get askew, what with the little register sleeves that go up and down and around. When the plate was tightened up by the two screws, being so flimsy, it could have buckled. It should straighten out with a bit of force.
You'll really curse, Marqs, when you take off the moving point and the spring washer that holds the plot together busts one of its little tangs . . . .
It would be really GOOD if new cb backplates were available. TT refers to the loose pivot syndrome - which happens to brass sets too and is never good. But there are only e-bay solutions it appears, and who knows what you'll get from there. Last year, I started making a few new backplates for my own purposes, but (like for ATD parts, see other posts) it's a labour of love . . . and is more complicated than it looks when it comes to broaching keyways and so on. The dimensions are mission-critical for the maintenance of correct internal timing on any mag, and the pain of getting it wrong after spending ages on the tools is hard to describe but I know it well . . . What we need is a small production turning operation - or better still a small foundry operation with accompanying finishing skills - to get into production with new units of a quality comparable to the brass type. They are a hell of a time-consuming thing to make as a one-off on a lathe and milling machine, although it can be done and I proudly possess one or two (which actually work fine).
It's the old thing: - who is willing to pay what it costs to make these things in pitifully small quantities? For 'cooking' everyday bikes like mine, not me, and I doubt if most classic owners would either. It requires scale Scale SCALE, which we just don't have as far as I can see, or folk like Wassell would have got there it already.
Cheers, Bill
