Broken points

[Angus]

Not strictly BSA so mods move if you want but a K2f Mag is a Mag.
I am guessing this is why the AJS model 20 stopped about a mile from home.

[Triton Thrasher]

Had they done many miles?

[groily]

Hmmm  . . . yup. The opening cb point is primary circuit 'live' on that sort of breaker, so a broken (or poorly adjusted) spring brushes the camring, and End of Sparks.
Those replica sets are in my opinion pretty horrible and can die very young - no intention of causing any offence, but I truly think they are and I don't think I'm alone in this.
The Lucas ones were better and also had a second fixed point not a rivet on the 'other' arm so the unit was truly reversible (so you could put it on your Vincent  )
But still - again, just me - far inferior to the original brass sort for more than one reason. Lucas said the steel ones were "low inertia" and that is probably true, but  . . . I think they were a cheapo bit of nastiness and more likely a way of not having to manufacture 'handed' versions according to direction of rotation.

First reason: on the brass backplate the opening point is to earth so a spring kissing the camring won't stop it (although it will wear it through if left unattended). Secondly: the points adjustment stays good for far longer and is often a much better 'mate' face to face; and thirdly, the ones with an auxiliary earth brush (not all of them have this though) help with avoiding the commonly-seen 'dimple(s)' on the drive end of the armature where the main earth brush sits, caused by the return HT current nibbling away at it.

If you could find a half-decent brass cb unit I think you'd be happier. They have their weaknesses too, like everything else, but they are almost always fixable. And because camring and backplate dimensions were standardised way back when, subject only to checking the position of the integral keyway on the male taper is in relatively the same place, a cb set from a BTH or a Bosch with their alloy arms and larger diameter pivot post for the opening point is a good option too. They wear better than even the brass Lucas items, have the auxiliary brush provision because many of their mags had no big earth brush like on a K2F or other post-war Lucas, and I happily use them for choice on some of mine. Anything apart from the steel backplate unit as far as i am concerned for my own bikes.

[Angus]

In my ownership she has done about 4000, I dont think she did many before I bought her with only 6000 on the clock since a rebuild.

I have a spare of a similar type, but with the 2nd fixed points (I dont own a vincent  ). I think I may buy the points set and repair this one so I still have a spare. Next Autojumble added brass points to my shopping list

[Triton Thrasher]

Those replica sets are in my opinion pretty horrible and can die very young - no intention of causing any offence, but I truly think they are and I don't think I'm alone in this.

You are not alone in this.  It’s one reason I went to electronic ignition.

[JulianS]

I too had one fail - pattern with black plastic heal to moving point, single contact on fixed point, rivet at the other end. The rivet was thin and failed.

The genuine Lucas ones are somewhat better, part 54440888 for anticlock and 54440887 for clock, the difference being the position of the fixed contact.  The genuine old stock also come with a retaining ring and fibre washer for the moving point, 2 shims for aligning the moving point plus the short backing spring which goes under the main spring to prevent a stress point between the main spring and the fixing bracket. This little spring causes earthing problems if misaligned and touching the base plate.

Some photos

First old stock genuine Lucas 54440888 for anticlock. Complete with all the little bits.

Second old stock genuine Lucas 54440887 for clock with some of the little bits missing.

Last showing the position of the short spring.