Perplexing Issue on UG 215-2 Movement

[HorologicalHobby]

So I purchased a new mainspring for a UG 215-2 as part of an overhaul, and it was working perfectly and I let it run in overnight. This morning I came to find it without power. I thought that's odd, it has a 48 hour reserve. Give it a bunch of winds and all seems fine. I'm adding the microrotor assembly and suddenly the mainspring unwinds completely. Crap I think, broken mainspring. I give it a few winds, *ping* it unwinds. A few more and it seems fine, I wind it full and it's just fine.... *ping*. That's strange, I open up the barrel and the mainspring is fine. Weird... So I think it's some kind of issue with a part called #1520 Coupling Clutch. It sits right on top of the square arbor above the barrel, and connects the handwind and autowind components. Any one have experience with an issue like this? The whole part is riveted together so I can't open it to examine it. I gave it a light oiling like a reversing wheel, maybe I'll try running it dry...

Attached are photos and the UG215 parts sheet.

 

Thanks for all your help, you are by far the best community I have ever had the pleasure of being a part of!

3793_Universal 215SC - 215.9SC.pdf

[Marc]

I'm not familiar with the UG movement specifically but would imaging that it follows the general design of most other auto winders (full and micro rotor) in that the power is constrained within the barrel on the input side via a click on the ratchet wheel and not through the auto wind coupling. In which case I doubt that the coupling clutch is the culprit.

My first suspicion would be the arbor hook not hooking securely into the hole on the inner end of the mainspring, or the bridle slipping way too soon against the barrel wall.

Make sure that the arbor hook locates properly in the inner coil. Did you lubricate the barrel walls, and if so what did you use? You should be using a braking grease which actually prevents the bridle slipping too soon, but then lubricates the bridle/wall interface when it does slip. If you use the wrong grease then it may well slip too soon.

Also, have you used the correct replacement spring? If the new spring is too short then when you get to a state of partial wind the inwards pull on the outer coils as you wind further can pull the bridle away from the barrel wall releasing all the power in one go.

[HorologicalHobby]

I actually just fixed it! Turns out that the barrel transfer/hour wheel was upside down and would slip when too much torque was applied. The whole barrel was turning, not the arbor. I did in fact check the arbor before, and the mainspring is a bestfit for UG 215. Also moebius automatic barrel wall grease was used. All is well, I feel like an idiot....