A mate of mine wondered why his headstock bearings kept failing on his BMW R45. It was because there was no earth wire from the headlamp to the frame so the earth tracked through the headstock bearings. Same applies to magneto armatures. If there is no other earth route the bearings will be shot in no time. Regarding flux and points opening... ideally the points should open just as the polarity switches in the armature. The moment of switching sets up an electrical flux which conducts (I should say inducts actually) into the coil and ramps up through the thousands of turns - that's the only way I can explain it - electrophysicists please don't get picky! If the points open too early there is no flux so no spark. The strongest flux is at the moment of switching, from that point onwards the flux is steadily collapsing but, for a while, still doing enough to conduct into the coil, so if the points open late you still get a spark, but a weaker one. So, timing the points to the internal structure of the magneto is a good thing to do, which is why Lucas provided an eccentric stud under the press fit button on the cam ring housing. By turning the stud with a screwdriver you can rotate the cam ring relative to the points. If you're very brave or a bit cavalier you can play about with this. From the earlier explanation you will deduce that the earlier the points open the better, so you can twiddle with the eccentric screw to make the points open as early as possible and if this hasn't killed the mag it will have made it better! You should only do this on a manual magneto in the full advance position and you will have to reset your engine/magneto timing afterwards as well. The problem with the internal timing is that the flux collapses very quickly so you need to catch it whilst it's falling but before it has fallen very far. How good your mag is in terms of its consistency i.e. the points open at exactly the same time every revolution, will affect how close to the point of maximum flux you dare set your eccentric screw. If your mag is absolutely top notch you can set the eccentric screw very finely adjusted to point of max flux but if your mag has some wobbly bits like a loose cam ring or worn heel to the points or dirty points etc. your points will open, electrically, at a slightly different time each revolution. In this situation you should not gamble with the eccentric screw because there will be some occasions when the points open earlier than usual and the mag won't spark - hello misfire! I thought I'd throw my two penn'orth in as Groily needs time off for good behaviour! As a p.s. I note somebody mentioned V twins. An interesting case. Normally, one cylinder fires at optimum flux, let's say 0 / 360 degrees on the cam ring, the other cylinder fires 60 degrees later (or 420 degrees later depending on how you look at it but the maths and geometry are the same), but only 30 degrees late on the cam ring because the mag rotates at half engine speed. Typically a V twin will fire at kickstart speed on the cylinder which fires on max flux then generates sufficient engine speed to fire on the cylinder relying on the low flux side of the mag. More mag speed equals more flux (sort of - electrophysicists back off!). This illustrates that having the eccentric screw on a conventional mag set to not quite maximum flux isn't a deal breaker because there's no way you are going to be 30 degrees out! Furthermore it explains why a manual mag, whilst stopping the bike kick back, will be difficult to start if retard the lever/cam ring too much. The closer to max flux on points opening, the easier the bike starts. Of course the strength of flux is directly proportional to magnet strength but don't get me started on that one! Good night!
