Has anyone tried to boost the magneto's output by adding rare earth magnets as additional "field coil" on the exterior of the tube? Does anyone have any data or information whether doing so will greatly/slightly improve the output?
A waste of time. The magnets you would be adding would be separated from the factory one by the aluminum of the magneto body. So any benefit would be marginal at best. Just get the magneto you have re-magnatized and it will work as good as when new.
Now I am assuming you are talking about a Lucas magdyno on a M20? By the 1930's they were using ALCINO magnets which are pretty good if re-magnatized. Even if in good shape, dissembling the magneto you will loose about 20% in magnetic strength but it will still work OK when put back together. But re-magnatizing will make it better.
Have you tried it or know of someone who did? The aluminum case is not magnetic so it should not be an impediment (other than the fact that the new magnet will be farther away from the rotor by the thickness of the case). Also, rare earths have much stronger field than Alnico. PS: I am not looking for good as new but better than new.
I'm a little puzzled by the reason for doing it on what is predominantly a side-valve motorcycle forum..If the engine will start first kick and rev-out without misfiring, what is the value of a bigger spark ?
An improved magnet would provide a stronger spark at kickstarting speeds and perhaps elevate the mag spark to the level of a coil ignition system...
On a V Twin where the two sparks occur close together and the magneto struggles to provide a good spark the second time I think it definitely would be worthwhile...
However, a magneto that is in good condition doesn't really have any difficulty when fitted to a single and the starting is good in that case...
It seems therefore that this is a solution looking for a problem in that application...If someone had difficulty kicking a single over (strongly) due to some physical problem then perhaps the improved spark would then become an advantage...Ian
Right on the head, Ian. The problem is this 70 year old guy (me) who just got out of the hospital after being hit by an SUV at highway speed on his (modern) Triumph. The knees are not working right and it seems like it's going to be a while before they get strong enough to kick over anything with force, even something with a 4.5 compression. Also, it seems like it would require less work to simply add magnets rather than take apart the 80-year old mag and remagnetize.
A magneto should always be magnetized with it fully assembled. It can be done with it apart but you will loose about 20% in magnetic remanence (field strength)once assembled. But it will still work fine, especially on a low compression side valve.
Some more information regarding the theory and practice of remagnetisation would be useful if anyone here is fully conversant with the subject..I always thought the mags were done when they were apart...Ian