Speedmaster “Moonwatch” Movements:
Background information
Written by Chuck Maddox USA! on 29 June 2001,
Last Revised: 21 November, 2006, 21:05 GMT
Certain Rights Reserved...

Recently in the Omega Forum we had a request for some background information on the movement Omega uses with the Speedmaster Professional “Moonwatch”... As we do get this type of request from time to time, I decided to expand and elaborate my initial response and preserve it for future reference/referral.

The Initial Query
The c.321 (a.k.a Lemania 2310/2320)
The c.861 (Lemania 1873) family
Distinguishing between 321/861's
Calibre Listing:
c.863, c.864, c.866, c.867
18th_Jewel / Yellow Gilt, Rhodium, New Nomenclature
Acknowledgments, Fair Use Provisions

The Initial Query:

The movement in the moonwatch... has it another background (has it any roots in a Lemania or another brand)... thanks in advance!
Yes, it does... But which one depends on which movement specific moonwatch movement you are talking about.
Over the years two main movements have been used in the watch that Omega calls "the Moonwatch"... The Omega c.321 and the Omega c.861 family...

The c.321 (a.k.a. Lemania 2310/2320):

The c.321 is based on a design development project titled "27 CHRO C12" (27 mm diameter, chronograph, with extra 12-hour register) took place in the 1940's by Albert Piguet and Jaques Reymond as a joint developement project between Omega and Lemania.  Launched in 1942, the 27 CHRO C12 later became known as the Lemania 2310, or Omega c.321).

It was used not only in the Omega Speedmaster from 1957 through middle 1965 but also the renamed and re-cased Omega Speedmaster Professional from middle 1965 through middle October 1968, but also in DeVille, Seamaster and non-model marked chronographs during this era. It also was used in Omega non-model marked Chronographs earlier in the 1950's under the 27 CHRO C12 calibre name...

The c.861 family (a.k.a. Lemania 187x family)...

The c.861 was developed by Lemania starting in 1965. As nothing is created in a vacuum, the Lemania 2310 was likely used as a starting point for the development of the new calibre...
Changes from the Lemania 2310/Omega c.321 to the c.861 included:
  1. The chronograph function was simplified from column wheel to a Shuttle/Cam system.
  2. The balance wheel was changed from a screwed balance to a smooth balance
  3. This allowed an increase in the frequency from 18,000 bph (2.5 HZ) to 21,600 bph (3 HZ)
  4. A flat balance spring was utilized...
  5. Another change was made to the shape of the bridge from it's previous "Arched", "Wishbone" or "Y" shape to a Trapezoidal shape... 
The revised movement was accepted for use by Omega, who started equipping Speedmasters in the October/November 1968 timeframe. The revised movement is known as the Lemania 1873 or Omega 861.

Here is a couple of pictures that I have modified to illustrate the main ways to distinguish between these two movements:

Distinguishing between c.321 and a c.86x based movements...

Omega c.321 (Lemania c.2310) movement
Omega c.1863 (Lemania c.1873) movement

Note: This movement is actually a c.1863 (see below)
Since the introduction of the c.861 there have been a few changes to the basic movement. However, there is a reason why I call this movement the "c.861 family"...

Listing of c.861 related calibre's produced through the years...




Starting with a comemorative edition in 1980 marking the 10th anniversary of the Apollo 11 lunar landing Omega used a highly decorated version of the c.863 movement with Côtes de Genéve on the bridge in conjunction with a special crystal display back to show off the movement. In 1987 the Display back model became part of the product line. Current Display Back models use the Rhodium plated c.1863 movement (see below)...


A special chronometre grade version of the base c.861 movement has been made available for limited production runs for commemorative models off and on from 1992 through 1994 (at least).


For some unknown reason (perhaps wishing to create an association) Omega named the Chronostop movement the c.865. The Chronostop has no real relation to the other models in the c.86x line other than Omega made and sold them.


A moonphase calendar complication version of the base c.861 has been produced for a special production run of 2,000 in 1985. Omega recently sold a white gold/white dial version of the moonphase and currently has a stainless steel/white dial version, both of which use the new Rhodium (c.1866) version of the c.866 movement.


A specially prepared hand made version of the c.861 made in 1994, that is a full-skeleton version of the c.861 created to commemorate the 50th anniversary of the hand-wound chronograph movement. Production was limited to 50 units...

The 18th Jewel / Switch from a "Copper" colored Gilt to Yellow:

In November 2006 there was a thread over at the Watch-U-Seek Omega forum where member GBonanno queried: "Where and Why" did Omega/Lemania add this additional jewel. Members rbt, jmsrolls (Fr. John even emailed me asking me if I knew the answer: I only knew the what and when, not the where and why), were among those who participated in the discussion, but forum moderator Eptaz sleuthed out the difference and posted a picture:

[Photo credit Eptaz]

Now, if you compare the part indicated inside the purple circle within the scan above, and compare with the picture provided by Eric's (Eptaz) fellow WUS moderator Strela below:

[click on picture above to open full sized version in a new window for side-by-side comparision, photo credit Strela]

You'll see that it certainly appears that this is where the 18th Jewel is located...

It appears from looking at Serial Numbers on various watches it appears that the 18th Jewel was added several years prior to the switch to Rhodium plating (discussed below). We also know that Omega switched from a Coppery colored Gilt Plating sometime in the 1992/1993 epoch. One would think that Omega probably did this switch around the same time.

However, there seems to be little rhyme or reason around the transition... I own for example, a display back model with an Apollo XI caseback (which points towards an earlier example) marked 17 Jewels, but it has the 18th Jewel, and is plated in a Gilt that looks more yellow than coppery to me. Which could mean several things: One, perhaps mine is a put-together, Two, perhaps Omega wasn't especially discriminate about assembly of parts and put some 18 jewel movements in watches with plates marked 17 Jewels. Interestingly enough, Eric (Eptaz) in an IM to me said that the person who first asked the question over at Watch-U-Seek had a displayback Speedmaster with the same configuration as my watch, so it might well be that Omega made some this way. I don't know, but it's very interesting.

OUTSTANDING detective work, Eric and my thanks go to all the folks who participated in that discussion over at WUS. I only wish I had known about it while it was goin' on!

From Gilt to Rhodium...

Starting in 1997 Omega changed the content of the movements it has put into the Speedmaster Professionals in two immediately noticeable and significant ways...

The movement was plated in Pink gold to begin with, then yellow-gold from 1992, then rhodium-plated in 1996. In 1996 the movement was renamed and re-launched as the c.1861 and is still manufactured today. A single part was changed from a metal component to a nylon-like synthetic part which wears better and is self-lubricating in all calibres except the display back model, with it the original metal part is retained because Omega didn't want display-back owners seeing the synthetic part. Additionally, a single additional jewel has been added bringing up the jewel count up to 18 from the 17 in previous calibres.

Nomenclature Change:

To differentiate earlier gilt movements from Rhodium ones, Omega calls the Rhodium versions c.186x... So the Rhodium version of the c.861 is called the c.1861, the c.863 is called the c.1863, the c.866 is called the c.1866, and so on...
To see the difference between these two different generations of movement examine this side by side pictoral: 
c.863 Display Back


c.1863 Display Back
Speedmaster Professional Display Back c.863

Speedmasters Professional Display Back c.1863:
Photo from an Omega catalog provided by Adam Gonzales
(click to enlarge)

Photo by Keith Downing
(click to enlarge)


I hope this helps you to understand some of the differences between these two base "Moonwatch" movements...
Having said all this, Omega has used several other movements (Omega c.1040, and several LCD Quartz) that it has marketed with the "Speedmaster Professional" moniker, and has sold at least one other model (the Speedmaster Day-Date Automatic c.1045 Case Ref. 376.0822) with a case nearly indistinguishable from the moonwatch case by the casual observer, but that's a tangent to the basic topic...

-- Chuck


I would like to thank the following people for their interest, efforts and contributions to this article:
  • Keith Downing for his contribution of a photo for an earlier article I wrote on Speedmaster Casebacks, which I have recycled here.
  • Adam Gonzales who sent me a 1996 Omega Catalog that I was able to scan a picture of a c.863 movement for the aforementioned article on Speedmaster Casebacks...
  • Dov from the Omega Forum for taking the time to email me some suggestions.
  • The participants over at Watch-U-Seek.com's Omega forum for the query, detective work and answer of the 18th Jewel riddle.
    • Especially Eptaz and Strela.
  • The folks in the TimeZone.com Omega Forum to numerious to mention here who posted suggestions to me in the forum...


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Permission is granted for Eric Katoso, Damon, Derek Ziglar, Frank N., Ross or Robert Jan to include portions within the FAQ's they are writing as long as credit (and a link to this article) is given. Permission for personal, educational or noncommercial use is granted. The author retains all other rights not specifically mentioned here... For all other use please contact the author.

Disclaimer: Opinions expressed are my own and knowing me should be taken with a grain or two of salt...