I've rebuilt 100+ generations and not seen this condition manifested before, or at least it's been so long ago I've forgotten it.
Follow me here:
It's motoring, that means the magnetic field generation is working, so both the armature and field windings are functioning to some degree.
With no 3rd brush that also means both of the other 2 brushes are working.
Dropping in the 3rd brush and having a change means it's also working.
The high current draw is a clue. It should draw a few of amps
max when motoring, not 8, and certainly not 11.5
Since the magnetic field can't be set in a neutral way, I'm going with there's a short somewhere in the field windings. That would cause an imbalance in the magnetic field and prevent a neutral setting AND cause high current draw.
Of those 100s of generators I've fixed, rarely did I find a set of field coils that didn't have some problem, shorts being VERY common. The lacquer coating on the winding wire only lasts so many years before it breaks down and allows it to touch the wires next to it causing shorts. Compressing those coils w/ the pole shoes and it goes from bad to worse. Soaking old field coils in certain degreasers is usually the kiss of death. Yup, done that...
Try this:
(Easy) You could test each of the 4 individual field packs resistance with a sensitive ohm meter. If the resistance on one tests lower than the others, you've found your problem and you can stop there and just replace your field coils.
(Harder) Or you can apply 6v to the whole field string and use a magnometer app on your smartphone to look at the eddy current generated by each of the 4 field coils. They alternate in polarity, but the readings should all be roughly the same at the same distance and position of the smartphone over each one. This requires you to remove all the field windings and getting those pole shoe screws out can be a bear. Also, you might eliminate the short on the bench only to have it return when the pole shoe is tightened down thereby compressing the wires together causing the short to reappear. Yes, this has happened to me more than once.
This is how I used to certify my rewrapped field coils before reuse, but I stopped doing this a few years ago. I *used* to rewrap field coils. Not any more. Now I only use new field coils in all of my rebuilds. The incidence of failure was so great that it just became more efficient to always use new field coils. My generator return rate dropped to almost 0 after I made this change.
I have oodles of field wrapping tape sitting in a box though if anyone needs some
AdminJeff
