The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: trevinoz on 04.03. 2013 21:07

Title: Magneto Pick-up Brushes.
Post by: trevinoz on 04.03. 2013 21:07
I just finished building a "new" magneto.
Rewound armature with new capacitor and new slip ring, new bearings. Even a new manual advance end plate.
And new pattern pick-ups.
With it nicely shimmed and rotating as smoothly as you could wish, I set it up on the bench to test, one plug lead to a spark plug and the other to a spark gap.
The plug fired only just OK but there was no spark at the gap.
Checked the pick-ups and slip ring and found that with only a few minutes running the brushes had appreciable wear.
The slip ring looked like a black crayon had been rubbed over it.
I dismantled the magneto and found a burn in the surface about 180 degrees from the contact segment.
Obviously the spark had been tracking around the slip ring and arcing under the brush.
I put another new slip ring onto the armature and changed the brushes to a set of original Lucas.
Back together and worked perfectly!
The damaged slip ring is under repair, I gouged out the burnt area and filled with epoxy. A bit of dressing when it cures and should be almost as good as new.
I have bought a few sets of pattern pick-ups lately and the brushes have been good but this set, from a different dealer than previously, caused a bit of grief.
In future I will closely inspect all pattern brushes.
This subject has been discussed before and I am just adding my two bob's worth.

Trev.
Title: Re: Magneto Pick-up Brushes.
Post by: metalflake11 on 04.03. 2013 21:42
Well done Trev, I don't think any of us have escaped the brush problem at one time or another. I'm very carefull where I get mag and dynamo partsfrom these days!