I Had my Lucas K2F magneto armature rewounded a year ago . Checked the bearing shim to bee ok and put an modern thinwalled busching into the old contactbreaker . Put the magneto back in bike , an A10 -56 , adjusted ignition the old way trugh sparkplughole at left cylinder, started it and put the bike aside for a year.
Now this winter I decided to fix the clutch and then I also put an degree disc on the engine to check with stroboscope if I had got the ignition setting ok. The left cylinder was ok 34° but the right was 38°. Contact gap left was 0,25mm and right 0,30mm .
So I decided to messure up the camring to see if it was unsymetric. Made an simpel fixture in aluminium with an protusion perfect fitting in the camring house bearing race . Put the complete camring house on it and made an line along one of the housing sides. This way I can twist the house 360° degree´s with a marking each 180° and with a dial test indicator messure the difference each 180° with accuracy 0,01mm . Messured differances that could bee in rating explaining this uneven ignition points. BUT it was all in wrong direction.
Put camringhouse back with a new contactbreaker set and now the timing was 34° and 36° / 0,25mm and 0,30mm. Also tried to twist the camringhouse 180° on the magneto to check what hapens. It was much worse but it confirmed that the camring shuld bee more unsymetric to get the same ignition points. Now I also found out that there is a tiny disk segment shim behind the outer race and camringhouse in axial direction that forces the bearing race to tilt a little bit and maby force the armature axle to bend a little bit during its rotation .
Is that shim a common way to fix this uneven igition point or is grinding on cam nock the right way ?
I wouldn't say that you use the shim to fix the problem but rather if the shim is not right or is loose, replacing it with one that is should fix the problem. It appears that in your case, the armature is not running Concentric with the mag housing. The insulating shim is often the cause of this. The original ones do wear out since they were made of something like waxed paper. I have made my own out of mylar shim stock and so far they have worked well. Nice thing is, mylar shim stock comes in a large range of thicknesses so you can get a nice snug fit.
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Re: Adjusting Lucas K2F cam ring
#246143 04/01/0910:12 pm04/01/0910:12 pm
I would also be more suspect of the bearing insulators than the cam ring. they are certainly a more affordable thing to replace than to permanently change your cam ring, even if they don't fix the problem right off, you can always work on the cam at a later time!
================= /1957 BSA A10 Spitfire Scrambler (in a friend's shed) /1960 BSA Super Rocket Basket Case (in the attic!) /1987 BMW K100LT nekkid
I have been spending some time with these things lately and a few things I notice .
1. I hate these things
2. if you havent changed the capacitor it would be a great idea to do so .
3. if the armature is not spinning true the baeraings , as you mention could be the culprit but you might check that the assembled armature is spinning true . the drive end/windings/points end pieces could easily be assmbled ever so slightly crooked and cause this whole mess .two screws holding the whole spinny mess together....just one of the reasons for observation 1.
4.As Alex mentioned on a post I made a while back , if you are looking for fresh insulators , Bob Kizer at Podtronics has them in all 3 bearing sizes
5. When it is all said and doneI have the same trouble withon of my mags and after checking everything I am certain the cam ring is worn more on one side thanthe other ,see observation 1.
You are all right . I shall first check insulation shim back the bearing befor grinding camring.
But I cant figure out why the ignition point / contact point breaker distance goes in the opposit direction that they should according to camring differences. I messure twisting it around bearing race surfaces and armature rotate in the same bearing surfaces. Could not be wrong unless the armature axle is bent during the rotation.
I am modifying my fixture so I also can mount the contact breaker assy in center of it .
Replaced the insulation schim by an home made one made of some strong 0,25 mm material we use for welding equipments at work . Bearing came into center . Had to put 0,05mm material on 1/3 of circumference to get bearing of center so contact gap became equal . Now I have 34° at left and 32° at right and I will let it bee there for the moment.