Service: EternaMatic Triple Date Chronograph / Valjoux 7751

IMG_0658Steve sent in his EternaMatic Triple Date for a service. This watch has quite a few complications:

  • day
  • date
  • month
  • moon phase
  • 3 register chronograph
  • automatic
  • 24 hour hand
  • sub-second hand
  • hacking second
  • quick-set date
  • quick-set moon phase
  • quick set day

From the top: the top sub-dial shows the day of the week on the left, and the month on the right. A lot of triple dates require you to manually forward the month, but this one does it automatically on every 31st. If the month is shorter, you have to advance the date by hand. It also has a hand for the minute recorder of the chronograph.

The sub dial at 9 o’clock has a short hand showing a 24 hour display (just in case you can’t tell if it’s day or night) and a longer second hand.

The date is shown by a central date hand with a crescent shaped red end.

The sub dial at 6 o’clock shows the moon phase, and the hour recorder hand. A total of 8 hands!


This EternaMatic is in a solid gold case.IMG_0660

Not too bad, but it’s been a long time since the last service, and the movement is dry.IMG_0661

Readers who are familiar with this blog will recognise the movement – it’s a Valjoux 7751, derived from the 7750.IMG_0666

The bottom plate with the day and month wheels at the top, the date wheel in the middle with 31 teeth, and a single tooth to advance the month wheel. Below the moon phase wheel with 59 teeth (=29.5 days between full moons). This isn’t very accurate, but the error is such that it only requires correction once a year.IMG_0669

I start off with the plate that covers the auto winder and parts of the chronograph.IMG_0671

At the top, the rose coloured wheel drives the click wheel to wind the mainspring. The bronze coloured wheel below is the reverser wheel (only uni-directional winding in this movement), and in the middle is the central chronograph runner. To the right of that the hammer to reset the second and minute recorder to 0, and below it the minute recorder.IMG_0672

One layer down….IMG_0676

The chronograph layer is almost gone, and we can see the intermediate winding wheel at the top left.IMG_0683

One plate down, and we are at gear train level. The silver coloured strip of metal in the middle is the hacking second lever that stops the balance when the crown is pulled out.IMG_0686

The top plate is almost cleared, and I turn the movement around.IMG_0687

Time for the triple date layer.IMG_0689

With the discs gone, you can see the little runners and gears that drive them.IMG_0691

The T-shaped lever at 9 o’clock drives the moon phase disc by one tooth every day.IMG_0694

Time to remove the next plate.IMG_0697

We are now at hour recorder level, and back to chronograph function.IMG_0701

Almost done taking apart the movement.IMG_0795

With the amount of complications, you get a lot of parts to go along with it.IMG_0796

Re-assembly starts with a new mainspring.IMG_0798

As always, I start with the base movement. No use putting anything else on until I’m sure that the movement is performing well.IMG_0799

And it does indeed.IMG_0800 Now I can start to put the chronograph back together.IMG_0801

And that’s tht done – only the rotor is missing from this side of the movement.IMG_0802

Now I can start on the first leel of the bottom plate. I start with the winding mechanism, and the clutch at 8 o’clock.IMG_0804 The first components of the triple date mechanism go in.IMG_0805

The moon phase lever at the top.IMG_0806

Ready for the wheels.IMG_0807

Day, month and moon phase discs are in.IMG_0809

With the dial and hands on, I case the movement.IMG_0810

Looks great in the gold case!IMG_0811

Yes, it’s 18k gold.IMG_0812

The movement has settled in, and shows the usual Valjoux 775n performance. They always do, and in my book, are the best performing chronograph movements.IMG_0813Having put 8 hands back into place, the watch is ready for testing.


14 thoughts on “Service: EternaMatic Triple Date Chronograph / Valjoux 7751

  1. Very nice movement. I have a 7750 of my own so I’m looking forward to seeing how it ticks – except that I’ll be working on the 7751.

    Did you have any problems with the calendar wheel drive? I hear that can happen if the stem is in the calendar set position.

  2. Interesting! I have a watch i identical to this but it doesn’t say “Les Historiques”.
    Anyways GREAT JOB!

  3. Interesting! I have a watch i identical to this but it doesn’t say “Les Historiques”.
    Anyways GREAT JOB

  4. As always a joy to see your work on a beautiful watch! I have a more contemporary cousin of this watch, the Eterna Soleure monopusher which is supposed to have been modified by Paul Gerber to convert the 7751 into a monopusher. The dial layout is similar, sans the hour recorder at 6. One of my favorite watches, even if the case is a bit big for my taste.!2139&parId=2D1225819D9EAB47!249&authkey=!APaKtfF__8uYVs4&v=3&ithint=photo%252cjpg

  5. Beautiful watch and great job restoring the intricate movement! I love these moon chronos, amongst the finest watches of the 50s and 60s… Christian I have a Valjoux 88 with a very faded moon disk, works fine except for a ‘sticking’ chrono that requires service, I hear that V88 parts are extremely hard to source but can a moon disk from another of the Valjoux series be substituted? Thanks, Chris

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