G12 magneto points problem.

[SCOTT TURKINGTON]

Evening all.
As a recent member to the ranks of "Jampot", I have spent the last six months reading all I could find in the forum archives.
I think I have got information overload.
However, the time has come to ask advice regarding my 1962 Matchless G12 csr.
I had a great run out on Tuesday, my bike starts easily and pulls strongly, easily maintaining 70mph up hill on a stretch of motorway.
Never missing a beat, I visited my parents about 40 miles away. had a spot of lunch and proceded home.
All went smoothly until about three miles from home the engine developed a miss, then cleared, backfired, spluttered etc. This continued the rest of the way home.
So I pulled the plugs and all looked reasonable. Checked the carb over, nothing appeared amiss.
trying to start up again there was no sign of life!
Magneto cap removed and there was a little roundish fibre "NUB" laying inside the magneto cap. I figured out this was the insulator that sits between the points and the tension arm,
How that managed to escape I have not a clue.
It does look like it has been round with the points for a mile or two.
On refitting said nub, she fired up immediately and idled great.
What is the correct term / name of this insulator? should it be dome headed or shaped similar to the one I have? where can I get one? or are they Unobtanium.
My apologies for my questions, and best regards to the group.
Scotty in sunny Northern Ireland.

https://ibb.co/NjD73yz
https://ibb.co/smCdJGK
https://ibb.co/RzyZpqM
https://ibb.co/VBnZ7R2

[Groily]

The 'nub' isn't actually an insulator because the opening point, spring blade and pivot etc are all 'earth' already - but if the 'nub' falls out (they do that!) then things can sometimes start misbehaving, especially if the spring blade moves and is able to touch the brass block in the middle with the other cb point on it, which is live. Or if the nub gets into the contact breaker or something.
The 'nub' can't be had as a new item but can easily be made with a bit of something and a gasket punch. A bit of fibre cut from a broad fibre washer, with a little dimple added for luck using a pointy punch after cutting the circle, can be good. Plastic, rubber, etc can 'do' too.
If the spring blade is loose on its pin - it's just pushed into the brass tower, it may need some help too. That 'help' can go as far as using a tiny screw to hold it on instead of a pin that's become loose, if a tiny tap can be had. 6BA sort of size is good.

[SCOTT TURKINGTON]

Thanks Groily, I have just fitted the nub back in place and all seems good. the spring blade appears fine, not loose by any description.
I will hopefully get out today to give it a real test.
On these older machines I find that confidence in reliability is hard come by. I need to get a lot more miles clocked up while this spell of good weather is here.
Scotty

[g5wqian]

hi scotty ;
there are 2 types of contact breaker points used in the k2f mag , theres the early brass bodied type which i think you have , and the later steel backplate type .
you can use either in the magneto if you swap the contact breaker mounting base over , i have swapped mine over to the later type so i can obtain spare points sets from the club spares as it seems the early sets are usually out of stock whenever i check the spares pages etc ..
youll need to find a later style points carrier to swap over to from the brass one but they are about .
https://www.amoc-parts.com//store/comer ... tegory=151
regards
ian

[SCOTT TURKINGTON]

Hi Ian, thanks for the info, you are correct my 62 has the brass assembly points. They are in relatively good condition.
I believe my problem was brought on by the fibre nub coming adrift between points and tension spring and going round with the points, it did get chewed up a bit.
I went out yesterday and covered about 20 miles without a miss.
Your advice is certainly sensible and I will look out for a steel type points carrier.
best regards Scotty