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Movement ring for sapphire case back on Speedmaster...do i need this thing?

john_coburg
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Good afternoon all,
Pardon a potentially numpty question here, but please humour me. I have purchased an aftermarket sapphire caseback for my 105.003 (which i think looks really pretty good for £100), but it comes with a chunky movement/O-ring... and i can't work out what it's for? If i put it in, nothing seems more solid/rigid, and the caseback itself doesn't screw on tightly to the mid case (annoying 1mm gap left). If i skip the step and leave it out, all seems fine (nothing seems to rattle)...yet it must surely be needed for something.
I'm bemused. Can anyone help?

The instructions were as follows:
"For fitment, you will need to remove your old caseback and dust cover. Then, place the bumper O-ring on the movement holder step as shown. Finally, screw on the new exhibition caseback and enjoy the view! Note: A previous version of the caseback required the movement screws to be removed. This is no longer the case."

20210328_160347 (1).jpg
 
Dan S
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We can't really tell without better photos, but normally an o-ring provides water resistance.
 
john_coburg
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Dan S Dan S
We can't really tell without better photos, but normally an o-ring provides water resistance.
Thanks Dan. I'll have a go at taking some shots, but i can't quite work out what the O-ring is replacing, as nothing had been removed, except the dust cover...which surely doesn't provide water resistance? if it's just a 'free' added feature, i guess i can do without it, particularly since it's bulk means i can't quite tighten the case back properly.
 
X350 XJR
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I think the o-ring is intended to make up for the thickness of the dust cover.
 
Dan S
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X350 XJR X350 XJR
I think the o-ring is intended to make up for the thickness of the dust cover.

I didn't think about that, but it makes sense. Without the caseback pushing down on the dust cover nipple, there is really nothing to keep the movement from flopping around except a reasonably snug fit in the case.
Edited:
 
Rado63
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Perhaps send an email to the supplier and ask why the O ring was included. Then you will know why they put it there and what issues if any if you leave it out.
 
Darlinboy
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Dan S Dan S
I didn't think about that, but it makes sense. Without the caseback pushing down on the dust cover nipple, there is really nothing to keep the movement from flopping around except a reasonably snug fit in the case.

The what is keeping the which from flopping around? 😲
 
Unfamiliar_Moon
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There’s an extensive thread or two on here about this, I can’t locate my bookmarks at the moment but do some searching on Preik
 
SkunkPrince
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That "dust cover" has squat to do with dust. It's for diverting magnetic fields. As stated, the o-ring is taking up the space of the magnetic shield.
 
Dan S
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SkunkPrince SkunkPrince
That "dust cover" has squat to do with dust. It's for diverting magnetic fields. As stated, the o-ring is taking up the space of the magnetic shield.

No, if the purpose were anti-magnetic, they would have used a different material. It's a dust cover. I'm sure this is really well-established. Just search.
 
SkunkPrince
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Dan S Dan S
No, if the purpose were anti-magnetic, they would have used a different material. It's a dust cover. This is really well-established. Just search.
It's a damned magnetic shield.

As for searching, I did a little, and this tells me that the "dust cover" theory is full of crap. Note this:

CALOTTE ANTI MAGNE 1450012/22. OME-096FE0037

Sure as shit ain't French for "dust cover".

https://www.watchuseek.com/threads/...of-the-omega-speedmaster-professional.339769/
 
SkunkPrince
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Just a general comment, just because people on a forum appear to have a consensus, doesn't mean they're right. I encourage everyone to do as much research as they can, and validate information with original sources as much as they can... and even then, question! I believed Omega when they said my CK 2627 was really a KO 2627 and spent a lot of money turning "silver" into "gold", when my eyes said, this whole thing is stainless, what are you talking about?
 
Dan S
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SkunkPrince SkunkPrince
It's a damned magnetic shield.

As for searching, I did a little, and this tells me that the "dust cover" theory is full of crap.

🤦
 
SkunkPrince
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Dan S Dan S
🤨
WTF does THAT mean?!

If Omega calls it an anti-magnetic cap, that's what it is.
 
Socks
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I've always wondered why you have a dust cap when the caseback is sealed and water resistant to 50m, but I never wanted to ask the question.. "Better to remain silent and be thought a fool than to speak and to remove all doubt".

But the anti-magnetic argument doesn't really add up either. How would it protect/deflect a magnetic field? Or is it a bit like the principle of cathodic protection?

I look forward to being enlightened!
 
JimInOz
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Socks Socks
......................................

But the anti-magnetic argument doesn't really add up either. How would it protect/deflect a magnetic field? Or is it a bit like cathodic protection?

I look forward to being enlightened!

So.....NOW you're telling me that THIS doesn't work?

1024px-Manwithtinfoilhat.jpg
 
JimInOz
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Early watches (including many Omegas) were given "anti-magnetic" or "non-magnetic" properties by using thick "soft iron" dials.

"Soft iron is iron that is easily magnetized and demagnetized with a small change of magnetic field. Soft iron is also referred to as soft magnetic materials. Soft iron does not retain their magnetism even after the removal of the applied magnetic field."

Magnetic shielding isn't new, or unique to Speedmasters with "dust covers".
 
S.H.
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Like in other watches (some UG compax, my DH Zenith, a lot of old Mido using Taubert cases, etc etc) , the cover is also used to securely fit the movement into the case. The center nipple pushes against the caseback like a spring when it is screwed fully and secures vertically the movement into the case. Only the stem prevents it to rattle vertically in the case if you don't use the cover, that is not good. So I assume the oring is used as a damper between movement ring and exhibition back, replacing the cover in this role.

In other watches, you can find some "ears" on the movement ring that have to be bent up, pushing against the caseback=> same role.

I hope I make sense, it is a bit hard to translate.
 
Socks
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So is it a dust cover, anti magnetic cover or a movement retaining plate? Re: anti-mag the Omega website doesn't differentiate anti-mag properties between the solid & display caseback models (both 15,000 gauss). Either way the cap is not fitted on the display caseback models so it can't be that important in dust or mag prevention.
 
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