In addition to the electric watches on this site, I also work on manuals and autos...and normally I would not include such watches on this site. But I was recently given an Omega Seamaster Cosmic 2000 to service and it was such an interesting exercise to open the case, I thought I'd write it up here as a photo essay. It seems I'm not alone in struggling to open these cases --- there are lots of horror stories if you search Goggle; with most people suggesting not to even attempt it without the correct Omega tools --- although no-one seems to know what these tools are or look like...

I should point out that my experiences below are based on the watch shown, which has a case number 166.129. I'm not sure if all Cosmic 2000 use this case.

Omega Cosmic 2000 Case: Before photo showing one-piece construction with crown removed.

Omega Cosmic 2000 Case: Before photo showing flush mineral crystal.

Omega Cosmic 2000 Case: Before photo showing flush back.

The flat mineral crystal sits in a nylon seal and is flush with the s/steel case rim; the back also sits in a nylon seal and is flush with the rest of the back...so the only way into this case is by separating the two piece crown and applying air pressure through the pendant tube to blow off the back and the tool you use to do this is usually the Bergeon 5011:

I have one of these pumps, and no way was it ever going to shift either the front glass or the back...probably because the nylon seals have moulded and hardened over the last thirty years. So I resorted to very carefully using one of these:

This worked --- after a short blast of air at 100psi! It blew the crystal off. But I was no better off, because the seal and chamfered steel ring were still firmly in the case and any attempt to dig these out would have ruined both as well as the dial. And at this stage, it still wasn't clear if the movement came out through the front or back.

I decided I had to get the back off, so pushed the crystal back on and tried the compressor again, but each time it would blow off the crystal despite me trying my hardest to keep this part on. After some carefully rigging up of the watch in a vice (!), in such a way that the crystal could not come off, I covered the watch with a cloth and gave it a quick shot of 120psi through the pendant tube. Success! The back popped off.

Once the back was off, it was clear that the movement came out through the front. So I removed the rotor and the balance from the Cal. 1011 movement and, using the appropriately sized nylon dies, pushed the movement (+ chamfered ring, nylon seal and crystal) out of the front of the case.

Big sigh of relief; got there in the end with no damage to movement, case or seals. Having serviced the Cal. 1011 movement, I took sometime in deciding how to re-assemble since I didn't want to have to open it again! In the end, I followed this sequence:

1. Fitted the large grey plastic movement holder to the movement and pushed the assembly into the case from the back. There is a flange in the case that the holder needs to butt up against
2. Pushed* in front crystal seal, followed by chamfered ring and then new mineral crystal
3. Re-fit balance and rotor
4. Pushed* on crown/stem and did finally time keeping regulation in all positions
5. Ran the watch on the auto watch winder for 5 days for final checking
6. Pushed* in rear seal and case back

Job done! *pushed in with a press

Showing all parts after cleaning. Top row: crystal, chamfered ring, seal and case. Bottom row: grey plastic movement holder, movement, rear seal, case back.	Case with movement and movement holder, seal, chamfered ring and crystal	Case, rear seal and case back.	Movement and movement ring now in the case.	Movement and movement ring now in the case.
Omega Seamaster Cosmic 2000: Finished watch.	Omega Seamaster Cosmic 2000: Finished watch.	Omega Seamaster Cosmic 2000: Finished watch.	Omega Seamaster Cosmic 2000: Finished watch.	Omega Seamaster Cosmic 2000: Finished watch; the cat didn't help much.
Omega Seamaster Cosmic 2000: Finished watch; the cat didn't help much.

I have no idea if this is the correct sequence for dismantling and reassembly, but it worked for me and didn't result in any damage to any parts. The two nylon seals were not re-newed.