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Jump hour movement, hour disc not advancing


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So I got this swiss jump hour watch. Serviced and everything looked nice. When worn, I noticed that the motion of the hour and minute discs stops when hour should change. The problem seems to be that there's not enough power transmitting to the gears that should advance the hour disc. 

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The dial side of the movement draws power from the mainspring barrel. Here there's this brass wheel under the barrel. The wheel consists of two identical wheels. In the picture you can see that there's this brass wheel on top and a chrome on the bottom. The chromed bottom wheel draws power from the barrel and when the watch is running the two wheels should rotate simultaneously held by friction (I think). When time is set, the bottom wheel doesn't move but the top brass moves and changes the time and that's how it should be. Is the problem in too little friction between those two wheels as I suspect? When minute count is 55 the wheel starts slipping and there's not enough power to change hour. Can I increase the friction somehow? I don't have experience in these movements or this kind of wheels. Any info or guesses appreciated.

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My guess was right. Slipping in that part was the cause. I could see a small gap between the wheels under a microscope so I figured out I might be able to push in a retaining ring you can see on top. I didn't dare use enough force in the jeweling tool so I eventually tapped it down in staking tool. Now the hour jumps and watch keeps somewhat decent time considering it's a pin lever escapement (Amida model something). At least the wheel train is pretty nice quality with small tolerances. 17 jewels.

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  • 4 months later...

I just cleaned/oiled a BFG 866 (single jewel) movement and replaced the mainspring barrel with a NOS part. The two wheels that are rivited to the mainspring barrel cover were slipping (serve as a canon pinion) and power was not being transmitted to the wheels that power the date, hour and minute dials.

The new mainspring barrel fixed the problem BUT now the movement runs, rotates the minute dial but stops at 55 minutes because there doesn't seem to be enough energy to push past the hour dial jump.

Everything is clean/oiled, all pivots are good. Just looking at the balance wheel it appears that there is not enough amplitude to keep the movement running when the extra resistance from the hour dial jump is encountered.

Is it possible that the beat error is great enough to cause this type of problem? I don't have a timegrapher but am thing of getting one???

 

mainspring barrel and wheels.jpg

Baumgartner_866.jpg

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