Now the armature of the K2Fmagneto is insulated by the paper bearing packing washers, And if these washers have deteriorated the bearings become pitted and burnt by carbon particles from the carbon brushes, as the armature shorts out through the bearings.
The reason for the insulator washers is to ensure that the return HT current passes by the earth brush, or brushes in cases where there is an auxiliary one on the cb unit, rather than partly or wholly via the bearings. Not really a carbon particle thing - just a case of avoiding using the bearings as a return path. You'll see on many a mag that the return current has worn a dimple, or 2 dimples, on the brass endpiece against which the earth brush bears . . . Having said that, there are many mags without insulated bearings, including some Bosch units. I have always regarded them as the Gold Standard among early magnetos at least - so I guess they thought a decent earth brush was 'good enough' back then.
So if you fit a aluminium magneto drive gear, doesn't this also short out the armature, and in turn reduces the magnetos output. And can burn out the secondary coil ?.
Nope. The armature's HT side is quite unaffected, so makes no odds to the most important bit - the HT coil. No short there, no reduction in performance of the coil. Many machines use steel or alloy drive arrangements anyway - AMC, Norton, some Beesas and Triumphs etc etc. If there were no earth brush, then the return current might work its way through the drive train as well as the bearings to get back to base, but as there always is or should be a brush, not a problem.
The Lucas service sheet for the k2f magneto can be found on this forum. And as far as I can make out the primary coil should be 5 ohms WITH 20SWG wire and 200 turns. And the secondary coil should read 5K ohms with 40 SWG wire and 11,000 turns. The condenser should have a value of 0.2 uf 400volts. The magnetos built in magnet dose not have a specific magnitization value, meaning it can be remagnitized with either N or S direction. But the K1F needs to be magnetized in the correct polarity.
Sort of. The wire gauges in different mags vary, and I think rather in thousandths than SWG. Primary resistance on K2Fs will be about
0.55 ohms; secondaries on K2Fs typically about 5000, but some were higher back in the day, and depending on the relative number of turns and the wire used you'll get some variations between winders.
Typical condensers will be between about 130 and 200nF. Good ones will be leakproof tested with 500v insulation testers to at least a Gigaohm. There are also important considerations with ref to their ability to handle current without fusing. Spikes in primary voltage can be surprisingly high 'at the break' and rolled paper capacitors rated in the 200-300v range would be at risk of damaging their self-healing properties. Bear in mind that voltage ratings are usually given in DC volts, but mag primary circuits are AC generators so you need to reduce the stated rating by about 0.7 (the inverse of I.41, the square root of 2) to get the equivalent AC rating.
On any multi cyl mag with a two-lobe cam, polarity isn't important, true. You get one neg and one pos spark whether you like it or not. Some people said in the old days you should swap your plugs over now and again to even the wear between them, as erosion patterns are different if the spark jumps from centre to earth electrode or vice-versa; I don't know anyone who does that! On singles, it's best to set things with a negative spark, either by magnetising in the sense that provides that, or by arranging the camring and contact breaker to get there.
