Is this armature fixable?

So sick of failing generators. I rebuilt my original one maybe 400 mile ago with a rebuilt armature. This morning I started it and it had a no charge condition. I did the first test in the Lucas diagnostic booklet, removing the wires and testing voltage from the D terminal to ground with no bridge between D an F terminals. It was 2V at idle but ran up to 27v at 3k so it has a short.

I pulled it apart and found this.

I gather this happened because they didn’t undercut the insulators between the segments and it rubbed slightly as the bushing wore. Assuming I do so now to keep it from getting worse, what’r the chances it will function again if I fill in the missing insulation with epoxy or something else?

Not sure how that is (easily, affordably) fixable: time to alternatorize!

The picture is a little hard to tell if the wire is shorted to the armature, but I have had good luck with pulling the wires apart, painting them with a high temperature enamel, and pushing them back down into place. A drop of glue to hold them down wouldn’t hurt. I would think you have nothing to loose by trying.

Do many people have switched to alternators, there must be a ton of generators hanging around.

I can’t tell either David. I’m not sure where to touch for continuity to test it. Anyone know? I’m not even 100% sure this is what the culprit is. It just seems like the most obvious flaw.

Bill, They come up from time to time. I bought one on Ebay a few months ago but that commutator is half worn away. It’s really hit or miss. I’d just like to try and resolve this one since it’s a fresh rebuild with no commutator wear.

Now you tell me? I only just installed a new expensive SS regulator :frowning:

I have a good Rover generator, which I believe is the same as the Jag: a fresh up and you’d be on your way again. Ping me if you are interested.

I’ll letcha know thanks!

The armature should be insulated from the windings, which are then brought out and rectified by the commutator. So if you were to measure with an Ohm meter from any connection on the commutator to the armature (doesn’t matter which part, could be the shaft or the laminations) it should be open (open is a relative term, more than a few thousands Ohms in this case). This of course is provided the remainder of the circuit is not hooked up, having the part out for inspection makes this easy.

After reading over the test (I know perhaps to much about electricity, not so much Lucas test procedures) the result you are getting would suggest that the issue is leakage from the commutator output (D) into the field (F). This doesn’t seem like an armature problem. I would look for a short between the field coil (the stationary one) and the commutator output. The insulation that is missing in your picture is really just there to keep dirt out of the windings, the actual insulation on the wires is the enamel paint.

Thanks David,

I’m headed out of town now but I’ll give this a shot next week when I get back.

The reason for the scraping is the root cause. Have you checked if the magnets are sitting where they’re supposed to ? I had the one original fan motor on my S3 loosing a magnet, making a scraping noise when the commutator mad contact…
Whether you can fix this as suggested, is an other question.

Cheers … Ole

The root cause of the electrical fault? I’m sure it’s the cause of the broken out insulation. As I mentioned, the rebuilder failed to undercut those strips and they’re standing slightly proud of the armature. I don’t believe the armature itself was contacting a magnet though. That would have been a pretty noticeable sound. I’ll double check the magnet screws. Maybe the rubbing caused enough vibration to make them loosen a bit.

That’s a different root cause then and not a lose magnet causing the scrape marks but the insulation.
I hope you manage a permanent fix, if there is such a thing with a car half a century under its belt :wink:

Hi Erica, my car is a little older than yours and it doesn’t have those inserts between the magnetic poles. As suggested they are there to keep the windings clean of graphite and copper filings. Maybe you could remove them? Paul

Erica, keep in mind what David has said. Obviously you want to address the physical problem while it is apart. However, your initial problem was no charge. When you did the Lucas check, it charged even when it was not supposed to, inconsistent with your problem. Per the test, you have a short between the D and the F post, causing it to charge too much. Not your original problem. But while it is apart, I would make sure there is no short between D and F. This short would not be the one you possibly see in the armature. The short in the armature would typically show low charging. Personally, due to residual magnetism in the fields, I doubt the validity of the Luca test- but it is a test by Lucas and I would check it out. So, if the area you see on the armature is shorted, it could be causing your low output. I am just reminding you to not ignore your test result.

You could do a simple test on the generator. With the generator out of the car or in the car with the fan belt and wires to the generator removed: Connect the two generator terminals together with a short jumper wire, using a battery connect the positive to either generator terminal and the negative to the generator case. If the generator now spins like a low powered motor then the generator is most probably OK.
Hugh Pite

Oh interesting. I didn’t know that was possible. I’ll try this because the last thing touched was when I replaced my regulator with a SS one a couple months back. Prior to that the dynamo had been working great.

I just checked that rebuilt armature against the armature from an NOS unit that’s never been run that I had sitting on the shelf. The rebuilt one shows fully open between the armature and anywhere on the commutator. The NOS one however shows 10 MOhm, and then slowly builds up to about 22 MOhm (not sure what that’s about).

It certainly isn’t shorting I guess so I’m not sure what to think about that first Lucas test procedure. There are no obvious shorts anywhere outside the armature either.

Both sound good, those kind of resistance levels are just a low level leakage (for fun measure between your hands), probably means there is a little oil (or similar) on the one.