Magneto Magnet strength ?

[cmfalco]

This idea has been around since shortly after rare earth magnets became available at reasonable price. However, there are several issues:

If the magnetic strength is too large it will induce currents large enough to damage the coil. Magnets come in different sizes so, like Goldilocks, they must not be too large nor too small.

Both sides (N and S) of the magnets will attach to the housing without problem, but they are strong enough to partially demagnetize the Alnico if the correct polarity isn't observed. This would make things worse rather than better. Because of hysteresis, swapping polarities once this mistake is made will not return the Alnico to its full strength.

[ralfpenkert]

However interesting details.
I suspected that it would mess things up.
Thanks - Ralf

[SEDoan]

I'm posting this up here as it pertains to the original question of magnetic strength.
I have been running a rebuilt MO1 mag in my '39 for 15 years, but it always seemed weak compared to the mag in my '47. The '39 was always more reluctant to start. (I don't know who rebuilt the mag, but it had the same large red capacitor in red epoxy and the same covering on the rewound coil that Falco shows in page 1 of his BritBike postings: https://www.britbike.com/forums/ubbthre ... ics/454088) Turning the mag by hand the magnetic resistance was barely noticeable yet it would spark and the bike ran well. Before remagnetizing a spark would jump a 5mm gap every revolution at 130rpm fully advanced, but would miss about 1/2 the time fully retarded.
Remagnetizing improved it so that it would spark about 90% of the time fully retarded at 130 rpm, but the magnetic resistance still felt weak.
I inserted an original (not rewound) armature and found that the original Lucas armature had much greater magnetic resistance so I started looking for clues why the rewound armature was weaker. The rebuilder or re-winder had turned the armature undersize by about 1/32" making the distance between the magnet and the armature greater. This seems like an obvious screw-up to beautify a part nobody can see.
Also, there were 2 holes or pits drilled in the laminations of the armature poles. Later Lucas armatures have similar holes in the same places, probably to aid in winding the coils, but these holes were larger diameter than the originals. Additionally, the letter A was stamped into the laminations above and below one of these holes. It seems likely that the stamping and drilling and perhaps the turning have shorted the armature laminations. I don't know how shorting the laminations would affect magnetic resistance, but guessing it doesn't improve it.

Given that my other armature had 80 year old windings, I decided to install new capacitors and remagnetize. The mag now sparks every time at 130 rpm advanced or retarded and advanced it sparks about 95% of the time at 80rpm. The bike now has about 250 miles on it and is starting and running well.