Hammond Model A Run Motor Problem

[ccw3432]

I'm looking for some advice on a Model A run motor problem. I picked up a Model A in unknown mechanical condition a while back and have begun digging into the restoration. The tone generator has been oiled and spun freely upon acquiring the organ. The start motor gets the generator up to speed, however the run motor only engages sometimes. Sometimes it runs but it often quickly cuts in and out multiple times after I release the start switch and then loses momentum. I measured the coils and I'm getting a reading of just over 180 ohms on one and no reading on the other.

I have the motor pulled and began taking it apart. I'm hoping the connector wire may have come loose so I'd like to get inside and take a look. I'm unable to get the motor opened up since the gear is attached to the spindle and I'm not sure how to remove it without damaging it. It seemed like a good time to stop and ask for some advice. Has anyone ventured down this road or perhaps successfully put the tremulant style gear onto a newer style motor? I'm not seeing any used tremulant geared run motors out there that I could just drop in.

[ccw3432]

[tiredoldgeezer]

While I'd never interrupt someone in the disassembly and rebuild of a motor, you might check the resistor, first.

The big brown resistor having problems can present very similar symptoms of "runs but doesn't run" sort of frustration. Alternately, a mis-wired start/run setup - this is often the result of a switch replacement. These are both FAR more likely to fail, or be hacked, than the motor proper.

Personally, I run two discreet, unconnected switches - a pushbutton for start and a toggle for run - with no resistor at all. I've done this for many years. And for that matter, the Model A might be that way, as memory is failing me at the moment.

Love the Model A. Simple. Elegant. Just right, I think.

TOG

[ccw3432]

Thanks for the reply and suggestions. I've never rebuilt a motor and don't really want to start now unless absolutely necessary! I just checked the resistor in the start/run switch circuit and it's measuring 254 ohms.

When I got the organ the run switch was wired incorrectly. It was only operating the start motor. I put in a new switch which I think is wired correctly but I could take another look if that may be the issue. I was suspecting the run motor because when I check the resistance from one of the black wires to one the brown wires I get about 180 ohms, but I don't get a reading when checking the other black and brown wire. When I check them how they were wired up together I'm getting 180 ohms. I'm new to working on organs and appreciate any insight.

[Tim_at_Jonas]

The first things I would suspect are a loose wire on the run switch, or a faulty run switch.

[JoeyB3]

I agree with Tim....Likely what he mentions. Run motors either work or they don't. It's that simple.

[geoelectro]

Clearly only reading 180 ohms on one coil and an open on the other indicates a bad motor winding. Each winding should be 180 ohms making 90 ohms in parallel. Either a motor rebuild or replacement is in order. There is another thread going where a run motor was rewound with clear pictures. Replacements are somewhat more rare for this older model.

Geo

[geoelectro]

Clearly only reading 180 ohms on one coil and an open on the other indicates a bad motor winding. Each winding should be 180 ohms making 90 ohms in parallel. Either a motor rebuild or replacement is in order. There is another thread going where a run motor was rewound with clear pictures. Replacements are somewhat more rare for this older model.

Geo

[Organ Monkey]

There should be many posts on this subject if you do a search, several of mine among them. I have a BC. The run motors on both generators were bad, having incorrect resistance. If I have to go by my foggy memory, I was told this is a common issue in early Hammonds. I found a local technician with some spare motors from later models. I think he had a puller tool and did a gear swap. Another problem was the mounting holes in the magnet stack were different. I didn't want to drill that out and have metal shavings in there, so some how I combined parts from the new and old motors to make it work. Then I think I had an interference issue with the new motor faceplate and the preamp mounting bar. I cut down the faceplate, put it all back together, and it has been working flawlessly ever since.

[Drawbar Dave]

In an earlier discussion we established that you can take a later motor and use the rotor from the earlier motor so that you have the correct gear for the tremulant. I have a spare M100 motor in my spares box in case one of my BC run motors ever crap out.

[ccw3432]

Thanks for the replies. I reached out to a forum member that has done this before and he kindly gave me some info on how he went about transplanting the stator and coil assembly from a newer style donor motor. I now have the original motor disassembled and I'm waiting on the donor motor to get here. I hope to get it all put together next week.

[Drawbar Dave]

That's great news.

[freiburg]

see my album. link below. i have disassembled and reassembled these motors quite often.

For reassembling you need a press ( do you call it like that in English?) and some additional tools to prevent the flywheel pressed in further.....

[Bobmann]

I just came across a bad run motor. The pictures you provided were a great help in helping me understand how these came apart.
This was in a Model M that dates around 1952.
However, the coils are enclosed in a sheet metal cover that is welded together.
How did you get this apart?

Thanks

Bob

[geoffbrown]

Great information thankyou for sharing of paticular value for people on a 240v 50hz supply

[Bobmann]

see my album. link below. i have disassembled and reassembled these motors quite often.

For reassembling you need a press ( do you call it like that in English?) and some additional tools to prevent the flywheel pressed in further.....

I do not understand this new and "improved" site format.
The comment did not appear as an update to the thread, so I will try this.

I just came across a bad run motor, and the pictures you posted were a great help in my figuring out how this works in regards to the connections to the coils.
The organ was a Modal M dated about 1952.

I tried to disassemble the bad motor, mostly because I wanted to see it for myself first hand and see if I could repair the bad coil.
I took the cover plates off, and the coils are encased in a sheet metal cover that is welded or perhaps soldered together that prevents me from getting to the coils.
How did you get this apart?

Thanks

Bob

[freiburg]

dear bob

it is regular solder. take a chisel and scrape the solder away. if you have almost everything mechanically removed you can cut through the rest and gently crack it open.

christian