Brightspark Magnetos

FAQ sections:

FAQs about the EasyCap
FAQs about magneto condensers
FAQs about magnetism and remagnetising
FAQs about ATDs and timing
FAQs specific to Lucas magnetos
FAQs about magnetos generally

In this section:

What do safety screws do?
Are suppressors and resistor sparking plugs OK to use with magnetos?
In an emergency, can the earth brush be used as an HT brush?
Why are some magnetos driven clockwise and others anti-clockwise?

FAQs

Is it true that in an emergency the earth brush of a rotating-coil magneto can be removed and used as an HT brush?

Yes, if the earth brush can be persuaded up the HT pick-up, but there are potential problems.

If you also have an auxiliary earth brush on the inner face of the cb backplate, everything should be fine. However, if not, removing the sole earth brush means that the HT current will need to find another way from the engine back to the magneto armature. If the drive pinion/sprocket is metal, then the HT current can flow through the drive gears or chain, which should be OK as a temporary measure. However, if you have a tufnol or plastic drive pinion on the magneto, the HT current will probably end up passing through your bearing races and balls and jumping the outer race insulators. The insulators can be damaged very quickly, and the bearings can also be damaged in the long term. 

If you do have an auxiliary earth brush, you might try using that instead as the makeshift HT brush. But you may find that it does not fit.