Several days ago my starter was working fine, but leaking a lot of oil due to worn bushings. I knew this was an issue I was going to have to eventually face, so months ago, I ordered the two-piece bushing set that comes with a seal. I took the starter apart and noticed that it had been serviced before because of two thin washers fore and aft of the armature. Last night, a friend, who has a set of adjustable reamers, came over and we fitted and installed the new bushings. The generator didn't want to spin and we thought that perhaps the worn fabric surrounding one of the leads was the issue. I put electrical tape around it and reassembled it. Now, all I get is an arc when put to a battery. Any suggestions as to what to look for that would be grounding out? Thanks.
Time for a rebuild. Oil soaked windings are invariably rotted, as you found on the leads. Something has moved, and one of your leads is grounding to the frame or brush plate. As you've found, things are pretty close in there...inspect very carefully after pulling the brushes out...use an ohmmeter to check for isolation as you disconnect each lead and you'll eventually discover where your short is.
As an aside, reaming the new bushing is not as innocuous as it may seem. The armature needs to be straight (usually are bent), and all 3 bushings, both in housing and one for bendix must all be in a line, and simply reaming the new bronze bushing by itself will not necessarily place it in the correct location. If the 3 are not in a line, the bendix will run in it's bushing very tightly. Excessive drag will increase current draw. Higher than normal current combined with degraded insulation resistance will lead to eventual breakdown and short to ground.
The only solution is to remove the windings, clean, rewrap, varnish them and reinstall. Not an inconsequential job. Alternative is to install new windings, but they are, in my opinion, not nearly as good as rewrapped original coils.
Best of luck, but honestly, I think you're going to have continued problems even if you initially succeed in fixing the existing short. Once the insulation is gone on the pigtails, the rest of the system is pretty well gone, too.
A starter is a controlled short circuit. So it will arc if you hook up power to it live. If you were installing it in the car, there shouldn't have been power to it. If you're bench testing it with a 6 V battery and cheap jumper cables, all you might get is an arc.
Does the armature turn freely? What did the insulation look like on the field windings and the armature? The field windings are just part of the circuit. There are a lot of other possibilities on shorts.
You might want to go with a rebuilt starter if you want to go the more trouble free route for your repair. If you were near Indy I'd look at it for you.
You mention both Starter and Generator. Which is it?
Does the armature turn by hand?
If not check the end play. The shoulder on the new bushing may need to be trimmed.
If you don't already have it, the MTFCA Electrical System book would be good investment.
I did mention both the starter and generator. Sorry - it was late when I typed this. It's the starter that is the issue.
The generator didn't want to spin at first because the bushings were too tight. Incidentally, it still has the original babbit bushing at the rear and someone in the past pressed in a thin brass bushing that is a better fit than the new one that I bought to replace it - so, we kept that one in place. My friend stuck the armature in the drill press to sand down any rough spots with 800 grit sand paper on the shaft and discovered that it was slightly bent, which I believe is the cause as to why it wasn't spinning in the first place.
After the sanding, it spun rather slowly and we thought that perhaps the worn fabric surrounding one of the leads was causing an intermittent ground. The fabric was oil soaked and what was left fell off. The coils look like they have been replaced at one time as they look farily new. I put electrical tape around it and went to bed.
Yesterday, I put it back together and nothing spun, only arcing when put to a battery with new, heavy duty jumper cables. I've checked and double-checked the connections and all are clean with no stray wires.
Maybe a rebuild is the easiest and best answer, but if I can save some dollars and fix this one, I'd rather go that route. I appreciate the suggestions that have been made and look forward to any others.
I would check that the post on the starter (where the battery cable attaches) for shorts. That's always a classic problem.