GMT A simple but complex complication issue

[ricardoch]

Hello,
I hope you all are fine.
10 or 12 years ago I bought a "rare" cheap movement, it had a big plate and hour ring, but no dial, hands or crown, as "longines" was printed in the auto rotor, it was a cheap toy to play with, but it slept in the drawer since then.

Recently I got back to watches and after long search, I find the movement looks like the Longines GMT model, and was lucky to find a "longines" cheap dial that fit 2824 and a chinese case that can hold the big plate, the movement seems to have married so many times that it will not mind new alien parts.

The problem I found is that the hour ring is driven by a big wheel that seem quite loose from his tiny pinion, and goes and stops depending on the relative position and hence friction of wheel and pinion.
You can see the pinion shaft is around half a millimeter diameter, not too much torque strength allowed in my oppinion.

It seems to be a common problem, almost all photos of that model I've seen on internet have the ring hour and hands poorly synchronised, but that's another history.

As wheel and pinion seems to be riveted together, I dont want to force unmounting risking to destroy it, so thought that "gluing" could be a reasonable solution, but I don't want to use a permanet glue, that can't be easily dissolved if I need to adjust, glue it again or whatever other reason.

I tried blue thread locker with a deceiving outcome, it ran fine for a couple days, and then they unglued, maybe because of smal adhesion surface for such big wheel.

Have you experience with this movement or know good adhesives that could bear such load, having into account that surfaces can't be easily cleaned or sanded?

Any help will be highly apreciated.
Best regards to all and take care.

(PS: Don't know how to comment each photo, sorry)
 

[Tudor]

So, you need to rivet the wheel to the pinion I think? I wouldn't use glue on that, if that's what you mean. Close the wheel around the pivot so it's secure.

I would say you should stake it and then get it as close to "24" as possible, as the date is flipping over. That may require adjusting the date driver wheel a tooth or two to get it all happy again. (you may get lucky and adjust one tooth on the 24-hour wheel) Fiddly disassembly and re-assembly, but necessary if you want it all to be right. Finally, the hands, as usual.

Make sure the pinion of the big 24-hour wheel is properly lubricated. Probably D5 (possibly heavier) if you can't find a chart on it.

That's actually a cool complication. And the buried magnifier for the date is also cool. I have the same type date magnifier on my old Tag Heuer with a Depraz module on top.  

[ricardoch]

Hi Tudor,
Thanks a lot for your advise.

I considered it as the best solution. Later I discovered that manufacturer did it with an hexagonal 0,5 mm stake, but seems it does not work as expected,  as could be seen in the photos of same watch I could find on Internet, almost all are out of "synchrony", so I have my doubts and, any case, I don't have any stake to try it.

The pinion diameter is around 0,5 mm diameter at the junction, trying to drive a 10 mm wheel, so the relative torque is so huge that it overcome the manufacturers expectations (I wonder who calculated it, maybe a floating comma fooled him).

(Tried to attach a better photo but the page do not allow me to do. I'll do later if possible)

As I suppose there may be some shoulder just below the wheel to support it, I though a fluid adhesive may penetrate it enough to increase the adhered surfaces and hence increase it's torque performance.
As I have no experience with such kind of junction I'm trying to test different adhesives that can be eliminated to check different makes if not successful. 

After much thinking and searching I think shellac may deserve a try, diluted it may penetrate everywhere and it could be easily cleaned. I'll post the outcome when I could do it.

 Again thanks for your help

[Tudor]

Shellac is a good idea to try. I'm just not sure if you can get it viscous enough to flow into the gaps. Perhaps try setting it from the flange side, so you can apply it to the gap of the heated pieces, and hopefully it is drawn in (like solder).

Which would be my next suggestion: Pure lead solder and a decent flux should flow in easily enough and be plenty strong (you may start breaking other parts).

[ricardoch]

Hi Tudor,
Again thanks for your help.
I'm thinking in alcohol diluted shellac, you could do it as much fluid as required and it evaporates reasonably fast in thin layers, hot shellac is too viscous to penetrate the junction walls, I tested other piece and it seem to stay in the surface.
I'm testing different densities and ways for it's application, as well as trying to discover if alcohol damages it's adherence, .by the moment it delays a lot evaporating thick layers, so must try different application procedures

I panic only thinking in soldering that piece, may be a good solution, but so far I only have soldered some dial feet, and is not that easy when coming to so tiny areas and could get really messy sometimes (My shaky hands do not help too much either)

Thanks again
Ricardo

 

[Tudor]

If I was to solder it, I would use an oven to do it, with the assembly jigged up to keep it exactly aligned. 
 

After it is cooled, just a bit of clean up. Worst case on the lathe (or in a dremel) to make it look nice again.