Auto winding issue with Cal 1120 (after Omega service)

I would suggest possibly a slipping bridle. The bridle on an auto-wind watch is a calibrated clutch that is designed to begin to slip within the mainspring barrel once the mainspring is fully wound. On occasion, when the bridle begins to slip, instead of slipping a bit at a time as the watch continues to wind, it slips a LOT, and can cost you half a day of reserve before it stops slipping. But you have been too nice for too long, and your warranty may well be no longer in effect. I don’t know what to tell you to do. But it looks like you’ll have to trust someone other than Omega. You are in Ontario. Why not send a PM to @Archer who is also in Ontario, and see what he suggests. But be prepared to pay to have the problem solved.

I have included a picture of a badly broken mainspring that I replaced on a similar model to yours. The “wishbone” shape at the top of the image is the bridle on the outer end of the mainspring which I suspect is slipping. I have also included a picture of the mainspring barrel after the spring was replaced.

If you can manually wind it and it runs for the right reserve, then it's nothing to do with the mainspring.

In the parts returned 2 things stick out - one is the barrel complete. They don't just change the mainspring in these, they replace the entire barrel with one that is already prepared - it wastes parts, but saves them time. These barrels are prepared using automated machinery, and this eliminates the variation that can come from individual watchmakers applying braking grease inside the barrel - so in other words makes it more unlikely that this is related to the mainspring.

The second one is what's not there - a new rotor bearing. Give the extent of the other parts that were replaced in the movement, I would have expected to see the bearing in the rotor replaced as well. In my experience, these are the single biggest issue in the automatic winding of these calibers, aside from the reversing wheel being worn (that has been replaced as I see the old one there).

There is a test that must be performed on the bearing to ensure that it is in good condition and properly cleaned. This is called the damping test...this is for a different caliber, but illustrates what the test is like.

I mount the rotor on peg wood, and support it using a couple of movement holders:



The rotor is turned to a position that is 90 degrees from the hanging position, and then you let it swing:



You time how long it takes to come to a complete stop:



This one a around 57 seconds is short of the requirement. Note that this time varies based on the caliber, so they are not all the same. So the first thing I do is clean the rotor again and try it again. There was no improvement, so the bearing is replaced:



Test is done again:



This time the bearing swings for 1 minute and 58 seconds, so well past what is required:



Once this is done, the bearing is very lightly oiled, and the test is run again. There is an acceptable drop in time allowed due to the drag that the oil creates, and if it's more than that, the rotor must be cleaned and oiled again. So my guess personally is that either the bearing is worn, or it was overlubricated during service.

How do you resolve this with Omega? Not sure what the answer is to that, but I would tell them again that it is not performing as expected, and ask why the rotor bearing wasn't changed.

Cheers, Al

I noticed it looks like they replaced the bridge with the serial number on it, I was wondering when Omega replace a part on the watch which has the serial number engraved, do they specially engrave a new part with the same number?

The earlier 1120's had the serial number on the barrel bridge, but since that is a part that wears out, they eventually smartened up and started putting it on the balance cock instead (which virtually never need replacing). So the result is that there are barrel bridges available with no serial number on them.

So I have replaced both types, and when the bridge is engraved, I send the old bridge back to Omega, who then sends it to Bienne. They engrave a new bridge with the old serial number, and keep the old bridge - there is no extra cost for this (other than cost for me to ship Omega the old bridge), just extra time as it takes several weeks. This is required because they clearly don't want two bridges out there with the same serial number on them. Here is an example of a newly engraved bridge that I received to replace a worn one:



You can see the smaller package inside has been cut open:



So seeing that the bridge they returned has the serial number on it, that puzzles me a bit...

There are two possibilities here:

1 - Omega replaced the bridge with one that has had the serial number engraved on it, and violated their own rules by sending back the old bridge.

2 - Omega replaced the bridge with one that doesn't have the serial number on it, which is really not good.

Good eye, as I didn't see that originally, but it raises some questions for sure...