K2F brushes

[KeithA]

Hello members;
Has anyone the knowledge of the correct standard length of the HT pick up brushes, also the earth brush.
Mine have a fine spring, with about 3/16" carbon rod sticking out. I think they need replacing.
Also my HT slipring is nice and shiny about an inch long. (Obviously where the brush is making contact).
The rest of the surface around the full circumference, is dull. Can't tell if it is brass or Bakelite.
Tried to clean it up with some 2000 grit paper, but no luck.
I dry assembled everything and with a dial gauge in one of the spark plug lead holes, I have found  the shiny part of the slipring sitting 4 thou higher than the rest of the slipring.
Would this not cause up and down movement of the brushes especially on the sides of the circular brushes.
I'm thinking now to assemble everything as per (well final assembly) and then skimming the surface of the slipring dead true, relative to the components I have, using a suitably shaped HHS cutting tip.
Any advise would be very much appreciated.
Thanks Keith A

[groily]

Hi Keith,
Sounds as if the brushes are fairly worn. The carbon on a new one is 11mm or 7/16th excluding the little tit that goes into the spring. The earth brush is much shorter though, so worn HT ones can work well there. Should also be 5mm diameter on a K2F.
The slipring on a twin cyl piece has a brass segment on it, the rest is bakelite/plastic. This is so that only one brush at a time touches the brass - which is where the energy from the coil arrives. Wouldn't do to have the coil trying to fire both sidesd at once! Most single cyl parts have a 360° brass strip.
The slipring can be lightly skimmed to get it round and flush, if you're happy it's in a decent state otherwise.
If you put a meter across the brass bit to the mag spindle, you should see the resistance of the HT coil, which ought to be somewhere in the 4500 to maybe 6500 ohms range usually. If it is Open Line then either the slipring is badly connected to the coil or there is a break in the winding.
Cheers, Bill

[KeithA]

Hello Bill Thanks for all that. Answers perfectly. I am awaiting service manuals for my rebuild, and I cant help myself to post a question in the mean time.
I have restored a few of the M01 Magnetos before, but this is the first K2F.
Thanks for your help again
Keith

[KeithA]

Magneto assembled and working OK on the bench.
Measured the resistance of the HT coil, and it came up 5210 ohms.
Keith

[trevinoz]

Keith, have you had the armature rewound and a new condenser fitted?
If not, maybe you should have. Especially if it is still the original winding.