Originally Posted by Magnetoman
Another problem the strobe helped me spot, that I had not noticed earlier, is the spring comes within only a few thou. of touching the cam twice per revolution. Although I could slip a piece of paper between the spring and the cam at the distance of closest approach, which means they weren't actually touching (which would have shorted the armature), they were too close. I looked at the assembly in my ZE1 and saw the short "helper spring" that is on the inside of the main spring and attached at the 5:00 end in the above photograph instead is at the 11:00 end in my ZE1. Although I had no way of knowing if its location in the ZE1 is the correct one, after I moved it in the ZEV the clearance improved significantly. This seems to be yet another mistake to add to the long list of mistakes the restorer made when rebuilding this magneto.

Sorry to interrupt, but in the interests of correcting misinformation, I think you'll find that, in that Bosch set up, the cam ring is at housing earth, and the contact-breaker back-plate, spring and moving point are all at armature earth. So if they touched, the only thing which they would short out would be the earth brush. They would not short the armature.

But of course the spring touching the cam would be a bad thing because of the resultant wear.

The Lucas 'low-inertia' CB assembly in the other photo is a different kettle of fish. There, the spring touching the cam would indeed short the armature.