I've just got my hands on this little gem, I know the strap is too big and a correct sized one is on the way, I couldn't let her go, so I raided the piggy bank







I hope you like

Matt

 

Hi,
This is a very nice caliber 27.96 (3/0 size sometimes referenced as 27.9) created in 1918, with negative hour setting. This caliber is qualified as 'rare' by Marco Richon in AJTT and Omega Saga.

The reference (27.9 SIBN) is engraved on the mainplate of yours, but it is not always the case. However, this movement is easy to spot : it doen'st have any screw for setting lever it is the only one I know from this period and of this size range (i.e; not pocketwatch or clock) that has the Omega word written with a modern font.

I know two different plate designs for cal 27.96, here is a picture of both side by side :


I have no information on the evolution of the design. According to Marco Richon, 27.96 and 27.9 are the same caliber created in 1917. Yours is of the same style as the one on the left on my picturea and is marked 27.9 SIBN (S stands for SavonetteN stands for Negative). The one on the left of my picture is the one identified in the 1926 spare parts catalog as 27.96 Savonette NN (Nouvelle Negative - New Negative.

Were they the same or different models? Were they produced in parallel, or is it an evolution in time? If anyone has some details, I would be interested.

 

Would it be a trench watch (although without the guards)?

Might look nice on a distressed bund style strap.

 

Thanks Tire,

So I've got something regarded as "Rare" in AJTT, I just liked the face and I hadn't got an Omega this old and for a couple of hundred quid I don't think I was robbed, it keeps great time -1min per day so far. Just one other thing, what is Negative hour setting?

Matt

 

Hi Matt

This may answer your question, sourced from http://www.vintagewatchstraps.com/watchmovement.html
Positive and Negative (American) Set

The mechanism that allows a watch to be both wound and set ("set" in this context refers to setting the hands to the correct time) by turning the crown or button is called the "keyless work". Before this was invented watches had to be wound and set by a key. There are broadly two forms of this mechanism, positive and negative set. In both forms the normal position of the crown against the case is the winding position and the crown and stem are pulled out from the case to put the mechanism in the hand set mode.

• Positive set keyless work is the most common form, at least most common in Europe. Because it is so common, "positive set" is usually omitted and it is just called "the keyless work". In this type of keyless work a long stem extends from the crown into the movement and is held in place in the movement by the setting lever. When the crown is pulled away from the watch case to set the time, the setting lever is moved, putting the keyless work into the hand set mode. The pull on the stem is a direct, positive, action on the keyless work, hence the name. A detent holds the mechanism in the hand set position until the crown is pushed back to its normal position against the case.
• Negative set (American) keyless work is spring biased to put the mechanism into the hand set mode, and this is the mode of the mechanism when the movement is out of the case. A short "crown" stem or "American stem" is fitted in the pendant or stem tube of the watch case. This stem doesn't extend into the movement and is not attached to it. Once the movement is put into the case the crown stem is used to push the keyless work into the winding position, against the spring. A detent in the pendant holds the crown stem normally in this position. When the crown stem is pulled out into the hand setting position, the spring in the movement pushes the keyless work into the hand set position - so the stem doesn't "pull" the keyless work into the hand set position. The keyless work assumes the hand set mode when it is not blocked by the crown stem, so the action of putting the keyless work into the hand set mode is by removing something which is stopping it, a negative rather than positive action, hence the name.

Watches by Cyma sometimes have movements with the American negative set keyless work and are engraved "US Pat 24 May 1904", reference to patent US 760647 for a negative set stem winding and setting mechanism (keyless work) granted to Sandoz on that date, a US version of a Swiss patent granted to Sandoz in 1903. You can see details of a movement with this feature on my Movement Identification page.

 

Thanks Jim.

Matt

 

I know that this is an old thread but I hope that this might get some attention. I own the same calibre 27.9. My case is not original, forgive the crown, during the restoration we could only find an old pocket watch crown that would fit the negative set movement. Is there any way we can find out more about this 'rare' movement?

Best,
Adam

 

To add to the confusion (or not): what do you guys think of this one. I have it since at least 20-odd years. Haven't opened the back-case -yet: it is approx 8000 km's away from where I am now, but the serial does date it around 1910, according to ChronoMaddox.
Dail is cracked ofcourse, and what I can remember, it is in a decent state. It is small: I think only 3 cm's in diameter; always thought it was a nurse's watch or something like that.
Case is 0.900 silver, as you can tell, and it runs (never used it really).
It has had some service or repairs in the past, looking at the scriblings in the outer case-back. Who knows.

I have never openend it: wasn't interested in vintage Omega's then... And I still do not particularly like it: more of a nice 'gem' than something I would use (and no, it is not for sale )

Well, have your 2 cnts at it... Thanks!