There should be little notches on the casebook that would allow you to use a simple tool such as this. Watch Opener Waterproof Watch Case Wrench - Watch Battery Tools | Esslinger & Co

Also as they said, the best way to know for sure what gasket you need is to find the case number on the inside.

Good luck.

 

Huh.....interesting, I hadn't really considered that type of opener. Below is a pic of the caseback and I was hoping to use one that hit all five holes like the last pic. Thoughts? Thanks!

 

Make a ball of quality (really sticky) duct tape with the sticky side out and use it to open the caseback. The only thing it usually won't open is a back/case that is corroded.

 

You don't need the Omega specific tool to open the case. And it will be more than $50 if bought from Omega (I have no idea what generic tools work).

The case back gasket is #088NS5140, SEAL O-RING D34.5 D36.5 Ø1

I recommend you let a watchmaker do this by the way...

Cheers, Al

 

Trust me, before I bothered you all, I tried a duct tape ball and a sticky rubber ball but no go. And the sticky ball opens all my other screwdown casebacks but not the Omega. I guess it is tighter and the deep ridges in the caseback keep the tape or ball from getting as sound of a grip as it does on a watch with a smoother caseback. If it is corrosion, I will probably CROAK, LOL!

As far as letting a pro open it, I can appreciate that point of view. But I live in Hawaii (and not on Oahu) and this Omega is a good three years away from needing a service but it runs 9 seconds slow per day consistently (still has its 44 hour power reserve, I tested it). That bugs me and I have the proper screwdriver to regulate it so I plan to give it a go IF I can get the darn caseback open using this page as my guide: http://seamasterreferencepage.com/srp/featured/regulating-my-omega-seamaster-gmt/

Keep the info coming!! Thanks!

 

Trust me, before I bothered you all, I tried a duct tape ball and a sticky rubber ball but no go. And the sticky ball opens all my other screwdown casebacks but not the Omega. I guess it is tighter and the deep ridges in the caseback keep the tape or ball from getting as sound of a grip as it does on a watch with a smoother caseback. If it is corrosion, I will probably CROAK, LOL!

As far as letting a pro open it, I can appreciate that point of view. But I live in Hawaii (and not on Oahu) and this Omega is a good three years away from needing a service but it runs 9 seconds slow per day consistently (still has its 44 hour power reserve, I tested it). That bugs me and I have the proper screwdriver to regulate it so I plan to give it a go IF I can get the darn caseback open using this page as my guide: Regulating My Omega Seamaster GMT | THE SEAMASTER REFERENCE PAGE

Keep the info coming!! Thanks!

Have you regulated a watch before? Look I don't know you or what your skill level is - you may be perfectly capable of doing this, but honestly most people are not.

Just trying to avoid you posting a thread like this recent one in the watchmaking forum:

https://www.watchuseek.com/f6/help-accidental-touched-hairspring-1398738.html

Yes he "touched" the balance spring, and completely mangled it. For his Seiko not a big deal to get it fixed. For your Omega, much bigger deal.

I am assuming you don't have a watchmaker on the island you reside on, and if so I understand where you are coming from. Just be careful if you decide to do this.

And if you get a Jaxa style opener as others have suggested, you should also get a case holder. Then place that case holder in a bench vise (most are designed for this) and then put the watch in the holder, and make sure it's tight. This will keep both hands free to operate the Jaxa remover, so you can adjust it to fit the holes, then use one hand on the back of the opener to steady it while you turn the handle and open the case back. Also note that using a Jaxa style 3 prong opener in a case with 5 holes on the case back is certainly not ideal from a geometry standpoint if you think about it. It will work as long as the 3rd prong is independently adjustable, but again not ideal. The 2 prong is even worse - again think about the geometry.

And please make sure you clean around the case back before removing it, to prevent dirt from entering the case. Also when you install that new gasket, apply some silicone grease to it before you put it in the groove of the case. If you don't the gasket could stretch/rip and then you won't have a seal. If you don't have a timing machine you will probably be chasing this adjustment for quite a while, so just put the case back on and give it a quick snug with your case removing ball until you get the rate right.

Good luck.

Cheers, Al

 

A standard 2 or 3 prong adjustable case wrench should give you enough leverage to open the tightest case, except in cases of extreme corrosion as ilitig8 pointed out.

 

So it appears the consensus is the three pronger is the way to go. It also might help me open a non-Omega case in the future I suppose. The 5 point "die" just seemed like such a natural solution but after having to return two at my own expense (separately) for not QUITE fitting, you guys are starting to make sense...

 

Admittedly, I have only regulated one watch in my lifetime and it was a success. Plus, that watch I regulated had the lever right over the hairspring where it is very vulnerable. My Omega seems way easier than that to regulate because it is a tiny screw (not a stubborn lever) NOT above any spring as far as I can tell from these photos (please take the minute to view):

Regulating My Omega Seamaster GMT | THE SEAMASTER REFERENCE PAGE

Also, I plan to hack (stop) the watch before I adjust the screw. Am I wrong here? I already own a vice and case holder, jewelers screwdrivers and silicone grease so I am thinking all I need is a case opener and a new gasket. Again, am I missing something here? Thanks again, all!

Edit: Don't worry about offending me by doubting my abilities, sometimes that is just what I need to keep it real...b-)

 

This is pretty well the exact tool I use to open omega casebacks. It usually comes with a multiple arrangement of bits to fit the different caseback holes accordingly.

I've never had a problem with it as long as you apply good pressure from both sides as you twist (that's standard for any tool being used.)

Good luck!

 

Given you failed with a rubber and sticky ball I would suggest getting what Vlance posted. It is usually called a Jaxa wrench (more accurately Jaxa style if it isn't a true Jaxa but the name is like Kleenex or Q-tip) solid ones can be found fairly cheap and actually the cheapest way to go is get a "watch tool kit" off Amazon that includes one. I think the one I got was in a roughly $13-15 dollar kit and had a few other tools that were decent enough to serve as backups like the screwdrivers. While the "Jaxa" included certainly isn't as good as a $100 version if you take your time and be careful they work just as well.

View attachment 2568346

 

OK, I hate when OP's don't follow up so here it is. I got everything I needed to regulate my Omega which was running consistently 10 seconds slow per day and had full power reserve when tested...

This model and procedure: Regulating My Omega Seamaster GMT | THE SEAMASTER REFERENCE PAGE

The recommended case wrench worked nicely. I removed the caseback and anti magnetic cover and was shocked to see how small that regulator "slot" was! Those huge macro shots of the movement were really misleading. So I buttoned her up loosely and had to go get a smaller set of jewelers screwdrivers so I did. Then I moved the regulator "slot" (calling it a "screw" doesn't seem correct because it is really an eccentric cam, is it not?) about three notches and buttoned her up loosely again. After 12 hours, basically no change in the timing, it was still about 10 seconds slow per day. I went back in and moved the "slot" all the way to the + sign (about three more notches) and this time it seemed to be about 12 or 13 seconds slow per day so it has gotten slightly worse for my expense and efforts. I know I could go back in and put the slot back where it started and get back to 10 seconds a day slow but I think a better solution might be a full movement service and pressure test since I want to swim with it and I have been scared to... THOUGHTS?

Is this place a good place for service on my Omega, anyone? SERVICE - ABC WATCHWERKS, INC.

I live in Hawaii so I will be shipping it somewhere I guess... 8-(

 

On the positive side. You live in Hawaii!

 

a suggestion would be Al Jenksy of Archer Watches, who has provided helpful advice on this thread:
ArcherWatches.ca