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Omega Constellation 1304 DeCasing Question

D
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Hello. I’m hoping someone might be able to assist please? I have an omega constellation 1304 automatic which has sustained drop-damage. I need to decase the movement to investigate, repair if necessary and service

I’ve not disassembled one of these previously and from what I can see, this has no tooling interfaces to facilitate screwing the case back, and I’m certain it’s not a snap on case back (at least I’ve never before worked on an automatic with a snap on case back)

The case may be monocoque or, it’s possible that the calibre sits in the case back together with crystal and the whole shooting match is pressed into the case?

I’d be grateful for advice, or better still any photos for clarification please

Kind regards, Darren

IMG_8215.webp IMG_8214.webp
 
rendo
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Looks like a snap-on case back to my amateur eyes, but I would wait until an expert confirms that.
 
D
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rendo rendo
Looks like a snap-on case back to my amateur eyes, but I would wait until an expert confirms that.
Thanks Rendo. I may be wrong, but almost certain it’s not a snap on. As I say it’s an automatic - not personally ever seen an auto with snap on case back🙂
 
Archer
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D Deggsy1969
Thanks Rendo. I may be wrong, but almost certain it’s not a snap on. As I say it’s an automatic - not personally ever seen an auto with snap on case back🙂
Now you have. Omega made plenty of them.

The case back gasket you will need to replace the one there now is part number 198ZW5022. It's a hard plastic gasket that deforms when the case back is pressed in place - these are designed to be single use items, and will not hold as tightly once they have been compressed once, so should be replaced.

When I am servicing a watch that uses this type of seal, I use the old one while performing my final timing checks (it will hold the case back in place well enough for that), then only once I know the watch is performing the way I want it to, do I use the new seal.
 
Dan S
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Never seen an automatic with snap-on caseback? Why would there be a correlation between hand-winding/automatic and the type of caseback? Even some of the early full-rotor automatic Seamasters (e.g. 2846) had snap on backs.

IMG_1654.webp
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D
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Archer Archer
Now you have. Omega made plenty of them.

The case back gasket you will need to replace the one there now is part number 198ZW5022. It's a hard plastic gasket that deforms when the case back is pressed in place - these are designed to be single use items, and will not hold as tightly once they have been compressed once, so should be replaced.

When I am servicing a watch that uses this type of seal, I use the old one while performing my final timing checks (it will hold the case back in place well enough for that), then only once I know the watch is performing the way I want it to, do I use the new seal.
Thank you for your detailed reply, I’m very grateful. This will be the first automatic I’ve worked on that has a snap-on case back. To be honest I have always associate snap-on case backs with cheaper watches, and watches that carry a low water resistance rating, so I’m quite surprised.

I do not yet have the watch in my possession, but will there be facility for a case knife or is a specific omega tool required please?

Thanks again for your help. Darren
Edited:
 
Archer
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All you need is a case knife or similar style tool.
 
D
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Archer Archer
All you need is a case knife or similar style tool.
Thank you. I greatly appreciate your time answering. It’s just arrived and I can now clearly see that it’s a snap-on case back. May I ask if there is an easy way to visually recognise the difference between the omega 1120 and the 1120A? I understand they have different pallets forks and thus lift angles. Also, anre there any crossover (compatibility) of parts with the movement it’s based on, the ETA 2892? Kind regards Darren
 
Archer
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D Deggsy1969
Thank you. I greatly appreciate your time answering. It’s just arrived and I can now clearly see that it’s a snap-on case back. May I ask if there is an easy way to visually recognise the difference between the omega 1120 and the 1120A? I understand they have different pallets forks and thus lift angles. Also, anre there any crossover (compatibility) of parts with the movement it’s based on, the ETA 2892? Kind regards Darren
There's only one 1120 pallet fork - 722112040010. It replaces the previous version.

Most of the parts in the 2892 will be compatible with the 1120, so internal parts like wheels, setting parts. The bridges are different (thicker) on the 1120, and the automatic bridge is slightly different. Of course the rotor bearings are not the same so not compatible.
 
D
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Wow!! I definitely found the right place for solid knowledge. I cannot thank you enough for your time in replying - I owe you a beer sir 🍺 . Not wanting to be a burden, but I'm curious (and think if anyone has the answer you probably will) … so what makes the difference in lift angles between omega 1120 (53o) and the eta 2892 (51o)? I always thought it was a function of pallet fork and / or escape wheel geometry? As I said, I don’t want to be a burden so please only answer if you feel like it. 🙂. Kind regards, Darren.
 
Archer
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D Deggsy1969
Wow!! I definitely found the right place for solid knowledge. I cannot thank you enough for your time in replying - I owe you a beer sir 🍺 . Not wanting to be a burden, but I'm curious (and think if anyone has the answer you probably will) … so what makes the difference in lift angles between omega 1120 (53o) and the eta 2892 (51o)? I always thought it was a function of pallet fork and / or escape wheel geometry? As I said, I don’t want to be a burden so please only answer if you feel like it. 🙂. Kind regards, Darren.
Not sure I've ever seen the lift angle listed as 53 for the 1120 - Omega lists it as 51.
 
D
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Archer Archer
Not sure I've ever seen the lift angle listed as 53 for the 1120 - Omega lists it as 51.
image.webp
I found 51degrees on the front of omega tech guide for the 1120 calibre. But just seen the same for the omega 1120A, and it’s listed as 51degrees. 🤷‍♂️
image.webp
 
Archer
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Who knows how that came to be. Typo? In any case, it’s 51.
 
D
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Archer Archer
Who knows how that came to be. Typo? In any case, it’s 51.
Thank you 🙏. Have a great weekend, and thanks again for your valued help. Kind regards, Darren
 
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