Omega 551 MS?

[jdm]

I'm getting a new MS to service my Constellation Chronometer. For the 551, Cousins actually returns 550 parts: GR25331X 1.05 x .11 x 360 x 9.5. But the 550 should be different, 17 jewels to begin with.
I suspect 551 and 552 are the same so correct is: GR2628X 1.10 x .105 x 360 x 11 Automatic

Can someone confirm? I do not want to dismantle the mov.t as I will not be doing the work myself on this piece.

[StuartBaker104]

According to the GR catalogue, both the 550 and 551 use the same MS, see page 10 of this link.

https://www.cousinsuk.com/PDF/categories/7810_GR Pages 141 - 150.pdf

[JohnR725]

Looks like the Omega 551 mainspring interchanges with quite a few Omega watches list below.. Then what's interesting is this is the best fit list of cross references the mainspring catalog doesn't 100% agree with this.  Although looking at the catalog it looks like all of the spring is if there is a variation are so close it's not going to matter.

OME 550 (CD1)
OME 551
OME 552
OME 560 (CD1)
OME 561 (CD1)
OME 562 (CD1)
OME 563 (CD1)
OME 564 (CD1)
OME 565 (CD1)
OME 750 (CD1)
OME 751 (CD1)
OME 752 (CD1)

 

[Tiktok]

15 hours ago, jdm said:

I'm getting a new MS to service my Constellation Chronometer. For the 551, Cousins actually returns 550 parts: GR25331X 1.05 x .11 x 360 x 9.5. But the 550 should be different, 17 jewels to begin with.
I suspect 551 and 552 are the same so correct is: GR2628X 1.10 x .105 x 360 x 11 Automatic

Can someone confirm? I do not want to dismantle the mov.t as I will not be doing the work myself on this piece.

Pm sent

 

[Tiktok]

The 550 and the 551 are listed as the same reference

[rodabod]

The 550 through to 752 listed above are all the same base caliber, therefore the same mainspring.

[jdm]

4 hours ago, rodabod said:

The 550 through to 752 listed above are all the same base caliber, therefore the same mainspring.

They could be the same base, but as mentioned above Generale Ressorts and Cousins UK list different mainsprings for e.g. 551 and 552.

Once again the link to GR catalog (with numerous hand corrections):
https://www.cousinsuk.com/PDF/categories/7810_GR Pages 141 - 150.pdf

[rodabod]

The additional jewels for the 24 jewels movements is for the auto winder, so shouldn't effect the loading of the gear train. The balances I believe are all the same, with some receiving additional adjustment for chronometer grading. I wonder if the GR reference is made from measurements of original springs fitted, and perhaps Omega updates them over time? Perhaps the metallurgy of the springs changed through the years, although all would be white alloy. The GR catalogue also quotes various springs for the Cal 26X range, but I believe these should probably all be the same. There's an argument that running a centre-seconds hand adds to the load (it will typically reduce amplitude by something like 5-10 degrees when adjusted) but that's not enough to significantly affect performance.

I see that on the Cousins website they list three different springs if you search for a Cal 565...

On my Cal 552 I have a 1.10 x .105 x 360 (11) spring which reaches 300 degrees amplitude, if that helps.

[JohnR725]

There's another thought here which is it doesn't really matter what you perceive the spring is supposed to be. Your unfortunately stuck with the problem of what spring can you get today. This is a common problem with American pocket watches there might have been three or four different sizes of a spring for a specific watch that came in various jewel counts. Then the early steel springs have a different strength then the modern white Springs and today you just get one spring..

Then If you look at the current Omega technical documents for the 551 in the parts list it refers to the mainspring as this 550/1208 So the number 550 is the base caliber Omega's telling you to use the 550 mainspring. The same thing with the mainspring barrel the complete barrel for the 550 is identical to the 551.