I don't have a source Russ, but I think it would be a worthy cause to see it working again. I have seen them occasionally offered on eBay etc, but have otherwise not paid much attention.
It could be that some oxidation has formed on the gear surfaces causing it to stick and there is not enough torque to get it going. Perhaps, a gentle back and forth rotation of the spur gear might free it up.
John, this evening I made an encouraging discovery. The synchronous motor is not dead, but just has a gummed up gear train as you suggested. I plugged it in, and heard a faint hum. So I gave the output chain sprocket some help and it began to turn, albeit in a labored manner. So I gave it squirt of spray silicone lubricant and will let it sit overnight. Perhaps that will un-gum that old gear train.
I brought the motor-gearbox assembly indoors to warm up. It runs much smoother now, particularly after sitting the the sun at a window shelf. It sounds like its old self, with kind of a rapid clicking sound. A few years ago when I plugged it in, that sound was missing. So I assumed the motor was dead. I'm pleased it was not. I'm letting it run in that warm environment to get it all un-gummed and turning at its designed rate.
Here are a couple of photos of the motor drive assembly:
While the chain looks quite robust in this photo, it is actually about 1/8 inch in width, with corresponding small pitch. I'll give it a lube with some bicycle chain spray. This view shows the high quality machining done with scraps left over from that old aluminum log truck bumper.
This Hurst motor has clockwise or ccw rotation depending on how it is wired. It provides 1/2 RPM at the output shaft. The capacitor shown in the diagram is external, supplied by the user. The 6-inch Mathis worm gear set came with this motor and appropriate spur gear pair. But due to space considerations, I opted for a chain drive.
This shows where the synchronous motor assembly would attach to drive the worm. Also seen is the babbit declination bearing housing, attachment fitting for the water-pipe counterweight shaft and the flange where the OTA attaches. This flange is just held onto the solid declination shaft by three tiny set screws. This works quite well, if these sets are occasionally snugged up. Friction for the declination movement is provided by small plugs of leather inserted under the two Allen head cap screws that are visible. These are tightened to get the desired amount of resistance.
Now I just need to acquire the right chain sprockets for the correct drive speed, and this mount will be good to go. No doubt these can be acquired online. I'll likely just go to a local machinist I know. He would know the correct chain gauge for the sprockets to match the chain I already have. He really does heavy duty machine work. But I'm sure he wouldn't mind a bit of light-duty business. Also it will be fun to converse with him again, since he is an amateur astronomer as well. No doubt a chain drive adds another component to the periodic error of the worm gear set. But since it is only used visually (not photographically), that is really of little consequence.
Needless to say this heavy duty GEM has a considerable weight capacity, at least for visual use. While it would no doubt easily carry the OTA of my 10-inch Dob, I'll just continue using it with my home made 8-inch reflector. I have decided to bring all of this information about my home made equatorial mount over into the Equipment > Mounts forum. The 8-inch telescope seems at home here. But much discussion of the mount best resides elsewhere.
Edited by Rustler46, 27 October 2020 - 06:26 PM.