Strange Doings in an EZM2 Hydro

[namor]

Here is a picture I took off an ebay listing.

eznm2.jpg

Its a Japanese dealer selling an EZM2 (403) Hydro. The pic shows the caseback open with a new battery, and the other pics show it buttoned back up with an oil fill. The the battery compartment is DRY, but the dial side is oil filled. If that is true, then its a great watch but clearly not immune to pressures much below a regular watch, if that.

What is strange about this to me is I've never seen anything written about this anywhere. Its no secret that I have replaced the battery on several EZM2s, and found how much fun it is to try and successfully get the flouro to fill the watch case without bubbles... It was easy only once, when I opened an EZM2 and found this exact same set=up: the battery was bone dry and there was a rubber dam separating the oil filled dial side from it within the case.

Not to be a conspiracy nut, but WTF was Sinn doing faking some of these oil filled watches?

[Chocodove]

Very interesting, though I don’t know enough about the technology to comment intelligently - should the entire case be filled oil?

[dnslater]

I'm assuming they removed the oil and clean the watch with the battery change prior to refilling? Maybe this photo was taken during that process?

[Wario406]

I had mine serviced by Sinn last year so I never got to see inside, but what I understand is that if the diaphragm seal leaks, then you get a bubble on the face side of the watch - meaning that the small amount of oil would be filling a lager space and hence would no longer be completely full.

I had wondered what that meant and assumed that the interior of the watch was completely filled with oil but never understood why a leaking diaphragm would cause the bubble.

If your premise is true - then it does not seem that the watch would be impervious to infinite water pressure as it would have a big air bubble inside the case - that would be a great big WTF!

[hoppyjr]

My guess is the owner tried to do their own battery change, managed to fill the dial side, then took photos. Once it’s all together, I doubt it would hold as it should.

[Ryeguy]

It was always my understanding that there should be no air present within the watch case at all.

Given the air is the compressible material, a watch case filled with air would have to be stout enough to resist compression.

When the case is filled with oil, which is not compressible, then the case can be slimmer as there is no compression to worry about.

When the case is partially filled with oil and partially filled with air, with a rubber diaphragm separating the two materials, you've kind of made a shock absorber.

[namor]

It was always my understanding that there should be no air present within the watch case at all.

Given the air is the compressible material, a watch case filled with air would have to be stout enough to resist compression.

When the case is filled with oil, which is not compressible, then the case can be slimmer as there is no compression to worry about.

When the case is partially filled with oil and partially filled with air, with a rubber diaphragm separating the two materials, you've kind of made a shock absorber.

This is my belief as well. Of the half dozen or so that I’ve opened, only one had a diaphragm keeping the battery compartment dry. There is, separately, a diaphragm of sorts built into the case back to allow for expansion and contraction of the oil due to temperature changes. But you can’t have a dry battery area and still be water resistant to great depths.

[hoppyjr]

It was always my understanding that there should be no air present within the watch case at all.

Given the air is the compressible material, a watch case filled with air would have to be stout enough to resist compression.

When the case is filled with oil, which is not compressible, then the case can be slimmer as there is no compression to worry about.

When the case is partially filled with oil and partially filled with air, with a rubber diaphragm separating the two materials, you've kind of made a shock absorber.

This is my belief as well. Of the half dozen or so that I’ve opened, only one had a diaphragm keeping the battery compartment dry. There is, separately, a diaphragm of sorts built into the case back to allow for expansion and contraction of the oil due to temperature changes. But you can’t have a dry battery area and still be water resistant to great depths.

Likely other people tried their own battery changes as you’ve done, but many don’t disclose or eventually send it back to Germany to be done correctly.

[Ryeguy]

It was always my understanding that there should be no air present within the watch case at all.

Given the air is the compressible material, a watch case filled with air would have to be stout enough to resist compression.

When the case is filled with oil, which is not compressible, then the case can be slimmer as there is no compression to worry about.

When the case is partially filled with oil and partially filled with air, with a rubber diaphragm separating the two materials, you've kind of made a shock absorber.

This is my belief as well. Of the half dozen or so that I’ve opened, only one had a diaphragm keeping the battery compartment dry. There is, separately, a diaphragm of sorts built into the case back to allow for expansion and contraction of the oil due to temperature changes. But you can’t have a dry battery area and still be water resistant to great depths.

How much oil is actually in one watch case? Doing my gorilla math suggests there is about an ounce worth of volume in the watch case, but the movement, dial, etc. must eat up at least half of that space.

Given silicone oils expand and contract about 10% over a 100 degree C temperature range (so, say -50F to +125F). My guess is the expansion would be a super small volume.

If I were to engineer an oil filled case, I think a very tiny piece of closed cell foam would be perfect for dealing with that kind of temp expansion or contraction.

If I were to get real nerdy, I would work out the thermal expansion of the watch case material itself to see if it naturally allowed for the silicone oil's thermal expansion. For example, 316 stainless will expand .064mm over that same 100 degree C temp range. Silver expands about twice as much as stainless steel, so using that material would require an even smaller buffer.

[namor]

Funny you should mention that - I did use a small piece of closed cell foam the first time I tried this, but then realized the caseback does a better job anyway. This is why many EZM2s will have a small bubble when unworn, but which disappears as soon as the watch is warmed by wearing it on a wrist.

The biggest difficulty is getting a full fill - my solution has been to submerge the entire watch in a bath of the oil, gently move it around to dislodge any stray bubbles, then screw on the caseback while still submerged. It works fine, but is wasteful of the not-inexpensive flouro oil. I've retired from this effort since most of the time, when the battery needs to be replaced the lume has also suffered degradation, and a trip to the spa is worth it.

[deepcdvr]

Wow - wonder if you can tell the build date, but could this be an early model?