Send questions or comments to [email protected]
.INITIAL INSPECTION AND INITIAL TESTS:
When I did my initial inspection of the Bosch ZEV I found the lock nut on the fixed point was loose and the gap was ~0.025", which is about 0.010" too large. A shim under part of the points assembly was in the wrong position resulting in the points being offset from each other by ~1/4 their diameter. I didn't photograph it that day, but the next day I reconstructed it roughly as it had looked, which is shown in the next photo.
Since the slip ring was new, and its condition indicated the magneto could not have run for more than an hour at most, it's possible the previous owner tried adjusting the points when the magneto failed and this is why they were loose. However, whether they were left this way by the restorer (which seems unlikely), or by the person who sold the motorcycle to my friend (more plausible), I don't know.
Another problem with the points that is not apparent from the above photograph is that the ID of one of the insulators was too small to fit over the OD of another, leaving a space between it and the brass housing. It's a little difficult to see, but from right to left at the bottom of the next photograph is the head of the screw that mounts the fixed point assembly to the rotating base, a brass washer, a flat insulator (with the gap mentioned above between it and the brass assembly), the assembly itself, and a cylindrical insulator that keeps the mounting screw from shorting the assembly to the rotating base. The OD of that cylindrical insulator is larger than the ID of the other insulator, resulting in the gap. Because this can be very easily fixed by slightly enlarging the ID of the flat insulator with a round file, the fact the restorer didn't notice it is the first of the direct evidence we have about the "quality" of his work.
The magnets didn't feel as strong as they should have felt, but this is hard to be sure of without an actual measurement. However, it wasn't worth the time it would have taken to measure the field strength with my magnetometer since I already knew I would be completely disassembling the magneto. Although the Alnico magnets in post-WWII magnetos retain enough of their magnetism for the magnetos to still function (although, at reduced capacity) after a restorer removes the armature and replaces it, that isn't the case for steel magnets. If it does have reduced magnetism in the present form it likely means the restorer did not understand this essential point about pre-Alnico magnets, or didn't have the facility to remagnetize them. Or both. But, taking it apart means I will have to remagnetize it no matter what.
The brass inside the points plate was not tarnished, indicating the magneto was restored sometime relatively recently (i.e. within the last decade or so). I assembled everything in the points cavity in their proper positions, set my test rig with the minimum gap (so it would spark even with weak magnets), and fired it up to see what things were like. The magneto exhibited classic bad condenser sparking at the points almost immediately (it probably had already failed before I even looked, but it took maybe 30 sec. to make sure everything was properly spinning before I looked at the points).
The next photograph shows the rig I use for extended tests. I built it around a 1/2-hp, 1725 rpm motor that operates either clockwise or counter-clockwise, and it has a board with adjustable gaps for magnetos of up to six-cylinders. Adjustable plates and brackets allow all types of platform- and flange-mounted magnetos to be easily attached.