Saving a chorus generator

[muckelroy]

Yesterday, I paid a visit to a church that had a Hammond BC, which had a non-functioning chorus generator. I was very disappointed to discover it was not a simple motor problem, but a drive shaft problem. I had hoped it was a "relatively" straight forward issue of a broken or missing brass paddle linkage. However, upon removing the chorus generator and inspecting it on the bench, I found the problem was not at all the paddle. All paddles were accounted for. The problem was that the brass gear was loose on its shaft, and not engaging the shaft. These gears are pressed on to the shaft at the factory, so you might call this a "bad pressing", but I'm not a machinist, so don't quote me on the diagnosis. All I know is that the gear was spinning freely on its shaft.

It looked like a blob of solder was stuck near the gear on the shaft, which was evidence that in the past, someone had repaired this thing with solder. As to whether their repair was a success or not, I can't say. This chorus generator has never worked in the time the organ was owned by this person, and no one had heard any difference.

Any sane person would have found a donor chorus generator, but I skirt the boundaries of sane sometimes, and the reason I did it was, I thought about the ways to fix this.
1. Replace the entire chorus generator.
2. Find a donor shaft segment (each segment has 4 gears on it), do major surgery to replace that shaft segment. (Does not make sense unless somebody happened to have disassembled (partly or completely) a donor chorus generator. The gear ratios are unique to this type of generator.)
3. Remove the faulty shaft, and have it welded, or braised. My knowledge of this topic is non-existent, but someone suggested braising, and I thought, forget it, because I can't do anything involving great amounts of heat so close to the phenolic clutch. It would melt or warp the phenolic. I'd have to remove the shaft first.
4. My father suggested cold solder. I don't know what he is referring to. (Anyone want to chime in?) I know what a cold solder joint is, and it's not a good thing.
5. Some other type of glue (epoxy).

After discussing the options at length with the owner, we agreed to give epoxy a shot. I used JB Weld 4400 strength 5 minute set 1 hour cure time epoxy. I cleaned the area repeatedly with CRC QD cleaner, and denatured alcohol. I then rubbed the shaft and gear with some 220 grit sandpaper (not easy to do, had to use forceps to reach in and do this.) Once I was satisfied everything was burnished and clean, then I mixed the epoxy and applied it with a thick syringe on the area. I had to be careful to watch for drips, because any epoxy that got on the gear teeth would ruin the gear. I did this on both sides of the gear. I waited about 30 minutes, gently rotated the shaft and did the same thing to the other "half" of the gear. I gave it more than a full hour to cure. I slowly turned the shaft by hand and it engaged. Finally, I applied power to the start motor, and it started up successfully. To stress test the repair, I hit start on the bench several times in succession just to see if it would compromise the joint in any way, and it did not.

I reinstalled the generator, and it is running beautifully. Because this was a repair I have never done before, and because the longevity of the fix is not known, I am being very generous with warrantying my work here for a long period of time, should this fail in the future.

This is only the second chorus generator I have ever heard working in person, and it happens to be only because I repaired it. That is very satisfying, to say the least.

I'll post photos later, just wanted to share the experience with you all while it was fresh on my mind.

[muckelroy]

This is a photo set of the slipping gear. You can see a “blob” of solder on the right side on the shaft from a past repair. I didn't want to do anything that would heat up things while in contact with the phenolic clutch. The epoxy dried clear and you can see it (just barely) applies in these photos. The third photo is the work space overall. It was a marathon of a job to do on site.

[tpappano]

Wow, nice job! From the perspective of having pulled both generators out of my 'new' BC, that is dedication to do that on site!

edit: Just thinking out loud if in the future it needed repair again, the gear could probably be silver-brazed in place if the wheels, gear, phenolic gear and bearings, etc. were all swaddled with wet cloth and a *very* fine tip is used on an oxy-acetylene torch.

[Drawbar Dave]

You had to pull the generators after all?! It'll be worth the effort.

[tpappano]

Hi Dave, getting solvent where it needed to go with enough force to flush 81 year old goo was turning into a "thing", plus the fact there were some uneven tone levels pushed me over the edge Friday 8) Going to replace capacitors, flush the clutches, naphtha flush the lube system and check/set all the levels on both generators.

[David Anderson]

My grandfather was a professor of machine design in a textile school, and he often relied on epoxy to fix things like this. I think he would have approved. It's what I would have done, exactly as you did it. With something like this, it will likely last indefinitely.

[Tonewheel]

You are a very good problem-solver. I love epoxy. It sometimes makes me appear to be a hero, with my wife, my kids, and others. I have filled threaded holes in 1/4 inch metal with epoxy, then re-tapped. worked.

Just don't tell anybody. It's a trick of the trade. ;-)

[Drawbar Dave]

That was a very courageous repair to pull of in the field. I wouldn't have been able to diagnose that let alone fix it. It's also nice that they wanted to have the organ fixed in this day and age. I hope this never happens on my BC 🤞

[muckelroy]

Thank you all for the kind words.

I was very surprised when the owner agreed to have the chorus generator either repaired, or replaced. He was eager to do it, and I was eager to make it happen.

I've never done anything so extensive in the field before. What brought this on was my first visit about a month ago. I was able to tilt the generator up a couple inches and see the drive shaft using my phone as a video camera. I took a crappy video (too close range to see clearly). In that video, though it is very, very blurry, you can see that one gear moves, and another does not. I could not see a brass paddle in that footage. So, I though "oh. paddle is missing." No, wrong. I was looking at two gears on the SAME segment of the drive shaft. Hindsight is the best foresight. As much of a pain in the rear as a broken/missing paddle would have been to fix, it is fixable. I have a generator from a spinet which I completely disassembled a few years ago, and I had hoped to use one of those paddles as a replacement. I came prepared to do a partial generator teardown on my table, but for better or worse, I did not have to tear down the generator at all.

The chorus generator is surprisingly easy to remove, as compared to the main generator. There are much fewer wires to desolder. Once I unlinked the chorus drawbar, got the preamp tray, expression pedal rod, and line panel tucked out of the way, it was not hard to come out.

While I had the generator out, I did take the liberty of replacing the start motor wiring. It was extremely brittle and cracked in places, and whenever I tried to strip a little bit away and splice a new fresh wire segment on, it would not strip, but just broke off. I replaced the entire start motor wiring run, which was fine as I had time to kill waiting for the epoxy to cure.

[muckelroy]

Just don't tell anybody. It's a trick of the trade. ;-)

That did cross my mind but I am more interested in sharing this than keeping it secret. The more chorus generators can be saved from the scrap pile, the better. And if someone wants to do this instead of calling me to do it, I'd let them. This took an entire day to do. My time is valuable.

[Sweet Pete]

Congrats,well done! Chorus genny sounds amazing!
I had an easier time replacing a shaft coupling spring a few years back.
Used a hemostat and pinched it back into the R100 genny that only had Bb....and F.
This old L100 genny have provided a motor and a spring so far! Never know what you'll need. I keep fast and slow epoxy in stock!
Had a D natural key survive an emergency for a year once! Got back to replace it,still working....changed it finally.
Anyone else encountered an A where a D should be?

[JoeyB3]

Damn....I'm glad I have a spare Chorus Genny in my basement! Ya never know....

[Drawbar Dave]

I shudder to think how many chorus gennys were discarded by people trying to make a B3 out of their BC. Can't beat that chorus. I use mine all the time.