Final Reassembly: Zenith El Primero Defy calibre 400

The day of reckoning has come – Cousins came back to me to tell me that the unlocking date spring they had supplied was correct. The manufacturer had substituted the original spring for a different construction! No wonder did I think it was the wrong part – it looks completely different. So now I can put together Dave’s Zenith!

The good news is that there must have been a reason that the spring broke in the first place, and that the substitution will get rid of that problem. If you read this because you are servicing a Zenith calibre 400, replace the spring as a preventive measure.

Here you can see the new spring in place – it assures a very swift date change at midnight.

Finally, I can put the bottom plate assembly back together.

The dial and hands go on – the bottom dial still needs the hand perfectly aligned – it doesn’t point right at the “12”.

As the crystal is scratched, I ordered a new sapphire crystal and gasket.

Case cleaned, and the new crystal fitted.

The case back gets a new gasket as well.

Movement cased. You can see that the chronograph hour dial hand now sits straight at 12.

Time for a bath … All is well.

Finally, the watch is back together and all is done. Chronographs are notoriously complicated, and this one adds the 10 bps high-speed movement on top. I haven’t kept exact records, but I’m guessing I have put at least 12 hours work into the job, if not more. But I’m very happy with the result, and it was well worth the time.

After 21 years, this El Primero has a new lease of life!

8 thoughts on “Final Reassembly: Zenith El Primero Defy calibre 400

  1. hi there im a watchmaker in dublin Ireland i just got in a tag monza that has this movement can you tell me if the oiling chart is availible online ?
    regards chris

  2. Reading this story raises an intriguing question in my mind – you are pressure testing in water – what happens if the case isn’t pressure tight?

    • You pressurize the container with the watch above the water, and then lower the watch. Now you decompress the container. If the watch leaks, air comes out of the case – not water in. 😉

  3. Just like to thank you publically Christian.
    The watch arrived back safe and sound today, and is presently spending time with it’s old friends in a display box.
    I will eventually wear it, but it’s fallen out of the rota system at the moment so it may be some time.
    Good job well completed.

    • Well, it took a while (Over 2 years in fact) but I’m actually wearing this watch today.
      A bit smaller than I remember, though that’s more than made up for by the width of it. 🙂
      It’s still keeping good time, though I must admit it looks a bit dated now, probably because it is I suppose.
      Thanks again Christian, will be in touch soon.

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