Ulysse Nardin UN-26 Marine Chronometer repair

UN-26 power peserve display module

Movement servicing is required every 2 – 3 years, if the watch is worn daily. The company Ulysse Nardin uses mechanisms based on the standard ETA 2892-A2 calibers with a modification and superstructure that is mounted on top of the main calibre. In many cases, services are limited to cleaning the main part of the mechanism, but we will also look into the module because this needs to be cleaned and lubricated as well.

Almost all watch manufacturers are hesitant to show mechanisms assembled on the basis of standard Swiss calibers such as ETA, and even assign them their own serial numbers or caliber/model names. Therefore, we will examine the interior and figure out what has been improved in these calibers, and ask what is the merit in creating an additional superstructure to the standard mechanism.

The trademark caliber on the reverse side differs from the basic ETA 2892-A2 only by the signature on the rotor. 28 jewels are indicated, although there are only 21 in the standard ETA movement.

We remove the module to see what has been modified in the base caliber. The arrows indicate the gear outputs to the module.

On the front, significant changes are noticeable. Below are listed the improvements to the basic ETA caliber:

  • Lengthened arbor of the mainspring barrel for the movement of the arrow of the power reserve indicator.
  • Lengthened post of the intermediate wheel to indicate the small seconds.
  • Added cutouts and racks for mounting and precision alignment of the module.
  • Extended the central posts and minute track so that the hands can be mounted above the module.

These are just a few improvements, but the details are quite important.

The UN-26 Module

Let’s take a look at the Ulysse Nardin module itself…

First of all, we note that the module is very thin.

Blue arrows indicate the inputs to the gear module from the base mechanism.

We remove the cover and inspect the contents, taking photos so as not to confuse the parts after disassembling and washing.

There are a lot of wheels in this module! And only to provide function to the small second and the power reserve indicators.

As you can see, the wheels are made without windows or spokes, making the components cheaper and easier to produce. For the module, this is quite normal, the speed of the axles is minimal, and the weight of the wheel does not really affect the function.

A very thin module requires jewels in the axles and grooves to support the wheels and stop them from skewing. Support stones prevent the large wheel from rubbing against the plate.

Wheels with a standard chemical polish look simple and functional, without any frills. The workmanship is approximately the same as in the basic ETA caliber.

A Buildable Marine Chronometer Dial

Now let’s take a closer look at the dial – a separate piece made up of 17 parts. The dial itself is made as a disc with holes for smaller discs. A plate with a second and indicator disc is mounted on the bottom of the main dial, so that the hands are sunk below the main plane of the dial. Each digit is made as a separate part with thin legs which are inserted into the base – the holes for legs are visible on the back.

Pay attention to the numbers – they are attached on legs to the main dial plate.

On the back of the watch face, you can see the tiny holes where the legs of the numerals are attached to the dial base. The Swiss traditionally do not pay any attention to the appearance of the back of the dial.

A Few Notes

  1. The module is made as an independent work of high-precision mechanics, the quality is decent and there are no obvious omissions.
  2. They have reworked/ replaced about a dozen parts in the basic mechanism, the improvements are quite significant, although not very noticeable from the outside.
  3. There are too many wheels in the module due to gear ratios. If the power reserve indicator was integrated into the caliber, the number of wheels could be reduced.
  4. Everything has been done functionally and technologically.
  5. The dial, although it appears quite normal, is subtly very complex.

As long as the watch is not subjected to any strong shocks, a caliber with such a superstructure can serve well for many decades. Although it is important that it is cleaned during every service.

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