still to be verified
In one line
The calibre 861 renamed in 1996, when the gold plating became rhodium. That is the whole of it. It drove the Speedmaster Moonwatch until January 2021, and it has a plastic part inside that Omega is happy to defend.
First things first: if you can see the movement through the back, it isn't an 1861
Omega sold four versions of the same thing side by side, and buyers mix them up constantly. The quick way to tell which one you are looking at is not the reference number. It is the caseback.
Sapphire caseback → calibre 1863 (3573.50, the “sapphire sandwich”)
Moon phase on the dial → calibre 1866, an 1861 with a module on top
From 2021 → calibre 3861, Master Chronometer
The 1863 is not the better movement. It is the same movement dressed up to be looked at: perlage on the mainplate, Côtes de Genève on the bridges, and the chronograph brake returned to steel. Omega did not want a customer staring at plastic through sapphire.
This is worth saying plainly, because it runs against instinct: the plastic part in the 1861 wears the chronograph wheel less than the steel one did. It was never a cost saving. It is the reason they fitted it.
1861 versus 1863: the same engine in a suit
The two get muddled because internally they are identical bar two details, and one of those is purely cosmetic.
| Calibre 1861 | Calibre 1863 | |
|---|---|---|
| Caseback | Solid | Clear sapphire |
| Front crystal | Hesalite | Sapphire |
| Finish | Functional, undecorated | Perlage and Côtes de Genève |
| Chronograph brake | Delrin, one piece | Steel, two pieces |
| Typical reference | 3570.50 | 3573.50 “sapphire sandwich” |
| Frequency and power reserve | 21,600 vph · 48 hours | Identical |
If the Moonwatch's argument is that it is the watch NASA certified, then the Hesalite and the solid back are part of that argument. The sapphire version is a different watch, and there is nothing wrong with that.
And the steel brake in the 1863 is no technical improvement. It is simply that Delrin, seen through a crystal, looks exactly like what it is.
What actually happened in 1996
By 1996 the 861 was twenty-eight years old. Omega did not redesign it. The gold plating gave way to rhodium and the calibre was given a new number. The eighteenth jewel had already arrived in 1993. All of this coincided with the move to reference 3570.50, which brought a new bracelet and Luminova in place of tritium, and that is where the belief that the movement was overhauled in 1996 comes from. It wasn't.
There it stayed for twenty-five years. The rest of the Omega catalogue moved across to the co-axial escapement from 1999 onwards; the Moonwatch carried on with a hand-wound, cam-operated chronograph drawn up in the 1960s, a solid caseback and a Hesalite crystal. That was deliberate. This is the watch NASA qualified, and touching it would have demolished the whole argument.
The 3861 arrived in January 2021: co-axial escapement, silicon hairspring, METAS Master Chronometer certification, resistance to 15,000 gauss. It is not a new movement, though. It is this one, rebuilt. The 21,600 vph beat is the same figure it ran at in 1968.
Why it matters
This is the Speedmaster people mean when they say Speedmaster: mechanically dependable, easy to find parts for, and a great deal cheaper than an original 321. It is the natural way in for anyone who wants a proper Moonwatch.
Three things almost nobody knows
- There is a plastic part inside, and it is there on purpose The chronograph brake — the part that grips the wheel when you stop the timer — has been made of Delrin, a DuPont polymer, since the early 1970s. Omega fitted it because it is kinder to the fine teeth of that wheel than the steel part it replaced. It has been in there for more than half a century.
- The Moonphase does not use a different calibre The 1866 is an 1861 with a moon-phase module built on top. It appears in reference 3576.50 on a bracelet and 3876.50 on a strap. Under the module sits the same cam-operated chronograph as always.
- The 3861 that replaced it isn't new either It is this movement with a co-axial escapement and a silicon hairspring: 26 jewels, around 50 hours of power reserve, magnetic resistance to 15,000 gauss. And the same 21,600 vph it ran at in 1968. Omega did not change the watch; it changed the escapement.
Technical data
| Type | Hand-wound chronograph |
|---|---|
| Base | Lemania 1873 ébauche, via calibre 861 |
| Chronograph control | Cam, with horizontal clutch |
| Frequency | 21,600 vph (3 Hz) |
| Jewels | 18 |
| Power reserve | 48 hours |
| Diameter | 27.00 mm |
| Thickness | 6.87 mm |
| Rate stated by Omega | -1 to +11 seconds a day |
| Chronograph brake | Delrin |
| Production | 1996 – January 2021 |
What a watchmaker checks before buying one
The test takes thirty seconds and nothing has to be opened. Start the chronograph, stop it, and watch the centre hand. If it jumps or drifts as it stops, the Delrin brake is worn. It is a consumable: it gets replaced at a service and costs next to nothing.
The pusher on an 1861 is stiffer than on a 321 and has more travel. That is the cam doing its job, not a fault. Anyone who sells you one on the grounds that it “needs adjusting because it's stiff” does not know what he is holding.
And the best thing about this calibre is not inside the watch at all. It is in the parts store. Omega built this architecture from 1968 to 2021. Parts exist, watchmakers know it by heart, and the documentation is out there. It is probably the easiest hand-wound luxury chronograph in the world to keep running.
Watches that used it
- Speedmaster Professional Moonwatch 3570.50 — from 1996
- Speedmaster Professional Moonwatch 311.30.42.30.01.005 — 2014 to 2021
- Speedmaster Professional 3573.50 “sapphire sandwich” — with calibre 1863
- Speedmaster Professional Moonphase 3576.50 and 3876.50 — with calibre 1866
Its predecessor is the same movement in gold plating: the calibre 861.