Omega Caliber 3861: From the Lemania 1873 to the Modern Co-Axial Moonwatch

There are mechanisms that were designed, used for a few years, and then replaced. And there are others that evolved so gradually that, when looking at their modern versions, one can still recognize the architecture and philosophy of their predecessors.

The Omega Calibre 3861 undoubtedly belongs to the second category.

The recent servicing of an Omega Speedmaster with Caliber 3861 at our workshop provided a good opportunity to examine this movement not only as a modern Co-Axial Master Chronometer caliber, but also as the current culmination of an evolutionary lineage that takes us back more than half a century.

A lineage that traces back through the Lemania, the 861, the 1861, and the 1863, culminating in a movement that, despite its modern technology, still clearly bears the DNA of its predecessors.

And perhaps that is the most interesting feature of the 3861.

This isn't a brand-new movement that was simply installed inside the Speedmaster.

This is Omega's effort to adapt a tried-and-true 20th-century design to the demands of modern watchmaking.

The Beginning: The Lemania Family, 1873

To understand the 3861, we must first go back to Lemania.

Lemania was one of the most important manufacturers of chronograph movements of the 20th century, and its relationship with Omega was particularly close.

The Lemania 1873 family features the basic architecture associated with the Omega 861: manual winding, a diameter of approximately 27.5 mm, a frequency of 21,600 vibrations per hour, and an integrated chronograph that uses a cam-switching system instead of a column wheel.

It is a structure that, even today, impresses more for its functional logic than for any attempt at a display of engineering prowess.

That's important.

This mechanism was designed to be durable, reliable, relatively simple to manufacture, and highly functional.

Features that would prove ideal for the Speedmaster.

1968: The Omega Calibre 861 replaces the Speedmaster

The year 1968 marks a turning point in the history of the Speedmaster.

Until then, the model had been powered by the renowned Calibre 321, an exceptional chronograph with a column wheel and a frequency of 18,000 A/h.

With the Calibre 861, Omega adopted a different philosophy.

The column wheel was replaced by a shuttle/cam system, and the frequency increased from 18,000 to 21,600 A/h — 3 Hz.

The 861 was less “romantic” mechanically than the 321, but it had significant practical advantages. It was more economical to produce, robust, and its higher frequency allowed for better chronometric performance.

That is one reason why this particular architecture has proven to be so enduring.

It’s also worth clarifying a common historical misconception: the Speedmasters worn by Armstrong and Aldrin on the Apollo 11 mission were still powered by the Caliber 321. However, the 861 became the next major generation of the Moonwatch, and NASA later certified the Speedmaster with the 861 for the Space Shuttle missions.

This laid the technical foundation that, through a series of developments, would eventually lead to today's 3861.

From 861 to 1861

The next major chapter began in the 1990s.

The Calibre 1861 was not an entirely new movement. It was essentially a further evolution of the latest generation of the 861, with the most notable visual difference being the switch to the newer rhodium-plated finish.

The change took place around 1996–1997, and the 1861 remained the heart of the Speedmaster Professional for more than two decades.

The basic philosophy remained virtually unchanged:

Manual winding, 21,600 A/h, cam-operated chronograph, and traditional Swiss lever escapement.

The 1861 is perhaps one of the best examples of how a mechanism doesn't have to be exotic to be good.

For a watchmaker, this is a logical, understandable design that has been tried and tested for decades.

And this is particularly important when it comes to service.

1863: When the mechanism becomes part of the aesthetic

At the same time, the Calibre 1863 makes its debut.

Mechanically, it is very similar to the 1861, but it was primarily intended for the Speedmaster with a sapphire display back. For this reason, greater emphasis was placed on the finish and visual presentation of the movement.

Here we also see an interesting shift in the Speedmaster's philosophy.

The mechanism is no longer something that simply has to function hidden behind a metal cover. It is now also part of the owner’s experience.

Nevertheless, beneath the different presentation lay the same basic family of mechanics.

And that's more or less how we arrive at 3861.

3861: the biggest change in decades

The Calibre 3861 was first introduced in 2019 and, starting in 2021, became the movement for the new generation of Speedmaster Professional Moonwatch.

This is where things get a lot more interesting.

At first glance—especially from the chronograph’s perspective—a watchmaker familiar with the 861 or the 1861 will immediately feel right at home.

This is particularly evident in the photos from this specific service.

The chronograph’s layout, the levers, the cams, the wheels, and the overall architecture of the movement immediately reveal its lineage.

But that's only half the story.

Because the 3861 features 26 jewels, approximately 50 hours of power reserve, a Co-Axial escapement, a free-sprung balance with a silicon Si14 hairspring, hacking seconds, and Master Chronometer certification. METAS certification includes, among other things, tests for accuracy, power reserve, water resistance, and exposure to magnetic fields of 15,000 gauss.

Essentially, Omega took the DNA of a movement that was born in a completely different era and brought it into the 21st century.

The Most Important Step: Co-Axial

This is where the biggest technical difference lies.

The 861, 1861, and 1863 models used the classic Swiss lever escapement.

The 3861 uses the Co-Axial escapement, an invention by George Daniels that Omega has been able to bring into mass production since 1999.

And the difference isn't just a different shape of anchor or escape wheel.

It concerns the way energy is transmitted.

Why was Co-Axial created?

In the classic Swiss lever escapement, the transmission of impulse involves a significant element of sliding friction between the teeth of the escape wheel and the anchor jewels.

This means that proper lubrication of the contact surfaces is of critical importance.

But the lubricant ages.

Over time, its behavior may change, shift, or deteriorate, affecting the friction conditions.

This is exactly the problem George Daniels tried to address.

In the Co-Axial escapement, the escapement geometry is designed so that the impulse is transmitted with much less sliding friction. As a result, the escapement’s operation is less dependent on changes in the lubricant over time.

And this is precisely where one of the system's greatest theoretical and practical advantages lies.

Less friction does not mean “no lubrication”

However, there is a misunderstanding here that is worth clarifying.

We often read that the Co-Axial “doesn’t need oil.”

It's not that simple.

Daniels’ original philosophy was indeed aimed at drastically reducing the need for lubrication on impulse surfaces. However, industrial applications continue to use controlled lubrication at specific points. Even Roger Smith has explained that lubricant is used on contact surfaces to counteract phenomena related to impact and oxidation.

And this is where the irony of the Co-Axial comes in from the service side:

An escapement designed to reduce dependence on lubrication requires an extremely high degree of precision from the watchmaker when it comes time to lubricate and adjust it.

On the bench: where No. 3861 shows its true colors

This is perhaps the aspect that a specification sheet cannot fully convey.

During the service of this particular 3861, once the bridges, chronograph, and train have been removed and we reach the escape mechanism, the difference between the two eras becomes apparent.

The close-up photos show the distinctive Co-Axial escape wheel, whose geometry makes it look almost exotic compared to a conventional escape wheel.

Next to it is the corresponding anchor, with a different arrangement of stones.

These two tiny components essentially represent decades of evolution in modern Omega.

And these are also the parts that require special attention.

Why Co-Axial requires more maintenance

The operational advantage of the Co-Axial system does not automatically translate into easier servicing.

In fact, the opposite is probably true.

Its proper operation depends on very specific geometry, the correct alignment of its components, and extremely precise lubrication.

The amounts of lubricant involved in the escapement area are extremely small. Too much lubricant can end up where it shouldn’t, while insufficient lubrication can cause various problems on the contact surfaces over the long term.

What is even more interesting is that a Co-Axial escapement may appear to function satisfactorily on a timing machine, without this alone proving that the escapement has been properly lubricated. Experienced watchmakers who work with Co-Axial movements have pointed out precisely this peculiarity.

Therefore, the difficulty is not simply:

"Can I get the mechanism to work?"

The real question is:

"Does it work exactly as it was designed to, and will it continue to do so in the long term?"

This is a very different requirement.

Free-sprung balance: yet another shift in philosophy

However, there is also a second significant difference.

The 3861 does not feature the traditional regulator system found in the 861/1861.

We have a free-sprung balance.

The adjustment, therefore, is not based on the traditional method of changing the effective length of the hairspring via the regulator. The approach is different and requires the appropriate knowledge and equipment.

In combination with the Si14 silicon balance spring, the system offers significant resistance to magnetism and excellent stability.

From the owner's perspective, this represents a significant technological advance.

From the watchmaker’s perspective, however, this means that a 3861 cannot simply be treated as “an 1861 with a different escapement.”

15,000 gauss: a change that’s truly useful

Anti-magnetic protection is perhaps one of the least flashy but most useful features of the 3861.

People today are constantly exposed to magnetic fields: electronic devices, speakers, cases with magnets, computers, induction cooktops, and dozens of other objects.

The Master Chronometer process involves exposing the watch to 15,000 gauss, while Omega uses modern anti-magnetic materials in the movement itself rather than relying solely on an internal soft-iron shield.

This means that anti-magnetic protection is a feature of the caliber itself.

For an everyday mechanical watch, this is a significant advantage.

And what's left of Lemania?

More than one would expect.

Looking at the photo of the assembled 3861 from the chronograph side, a watchmaker familiar with the 861 and 1861 models will immediately recognize the family.

The underlying logic is the same.

The same philosophy as a manual, cam-operated chronograph.

We don't have a column wheel.

We don't have an automatic winding mechanism.

We haven't tried to turn the Speedmaster into something it never was.

This is perhaps the greatest achievement of the 3861.

Omega could simply equip the Moonwatch with a completely modern movement.

Instead, he chose the more difficult path: to modernize the old architecture without losing its character.

861 → 1861 → 3861: evolution, not a fresh start

If we were to place the three mechanisms on an imaginary straight line, the progression could be described something like this:

Lemania 1873 / Omega 861
The movement. 21,600 A/h, manual winding, cam-operated chronograph.

Omega 1861 / 1863
The maturation of this architecture and its transition into the modern era of watchmaking, with the 1863 placing greater emphasis on the finish for display-back applications.

Omega 3861
The same heritage, reimagined to meet modern demands: Co-Axial escapement, free-sprung balance, Si14 hairspring, hacking seconds, enhanced anti-magnetic protection, and Master Chronometer certification.

They are not three unrelated mechanisms.

These are three different phases of the same idea.

So, is the 3861 the best?

From a purely technical standpoint, the 3861 offers capabilities that the 861 or the 1861 were simply never designed to provide.

Greater resistance to magnetism, modern chronometric certification, a silicon hairspring, a Co-Axial escapement, and approximately 50 hours of power reserve.

But in terms of service, there's an interesting trade-off.

The 861 and 1861 are exceptionally well-developed, traditional movements. Their design is straightforward, and their behavior is very familiar to experienced watchmakers.

3861 introduces levels of technology that require more expertise, different training, the right equipment, and much greater precision at specific stages of the work.

That doesn't mean it's any less reliable.

It means he is less tolerant of the wrong approach.

And that is an important distinction.

A mechanism bridging two eras

After the service, with the 3861 reassembled on the workbench, perhaps the most interesting view isn't the magnified Co-Axial wheel.

That's the whole mechanism.

Because there we see two different eras of watchmaking at the same time.

On the one hand, there is the logic behind Lemania’s mechanical chronograph: manual winding, gears, levers, cams, and a design that has evolved over decades of actual use.

On the other hand, we have silicon, antimagnetic materials, a free-sprung oscillator, a Co-Axial escapement, and METAS certification.

Both coexist within a mechanism measuring just a few centimeters.

Perhaps that is why the Calibre 3861 is more interesting than a completely new movement.

He isn't trying to erase the past.

He uses it as a basis.

The 3861 isn't just a 1861 with a Co-Axial escapement. And it's certainly no longer the Lemania 1873.

But if you look closely at the mechanism laid out on the workbench, its origin is still there.

More than fifty years of engineering evolution are evident within the same architecture.

And perhaps that is, after all, the most authentic feature of the modern Moonwatch:

It has changed in almost every way it needed to, while still reminding us of where it all began.