Repair + Service: Zentith El Primero Rainbow Flyback calibre 405Z

IMG_3111Robert sent this El Primero in, as it doesn’t reset properly, and the chronograph in general doesn’t work as it should. Winding is a bit noisy, too. He has had the watch from new, and it’s only 7 years old [correction – Robert told me it’s 10 years old], so I don’t expect any major damage.451-02

There are lots of dirt particles in the watch, and they must come from within, as the watch is waterproof.IMG_3117

The El Primero, the pinnacle of chronograph movements, beating at 10 beats/second.IMG_3119

My Witschi timegrapher refuses to pick up a signal, and my cheap Chinese one shows this image. The balance is hardly swinging, and that erratically. IMG_3122

With the rotor removed, I can work my way through the chronograph layer.IMG_3128

The central chronograph runner has its top pivot broken – no wonder did the movement not reset properly. I only discover that when I reassemble the movement, though, but as it’s in the photo here, I thought I’d mention it.IMG_3148

There is a lot of dirt here as well, and there is a reason for that…451-03

The pinion of the ratchet wheel driving wheel (1482) is half worn away. This pinion transmits the winding power, no matter if automatic or manual winding. But it shouldn’t be that worn after 7 years!IMG_3152

Under the crown wheel, a lot of dirt as well.IMG_3159

Now for the bottom plate…IMG_3162

Quite a complex winding/setting construction, with a quick-set date on the third crown position.IMG_3166

As usual,l the unlocking date spring is broken, leading to a very sluggish date change. There is a replacement of different construction available, that will hopefully not break.IMG_3176

All clean and ready to go.IMG_3246

Even though the barrel of the 405Z can be opened, I can’t get hold of a replacement spring, and I fit the old one. We will see later when we can an amplitude if that was the right decision.IMG_3346

I start off with the base movement. The new ratchet wheel driving wheel is in place.IMG_4144

Looks like the old mainspring is still very good!IMG_3423The new chronograph runner has arrived. Not cheap at £87.34!IMG_3427

The new unlocking date spring in place, and it looks a lot sturdier than the previous one.IMG_3425

The chronograph is working, and the depthing adjusted.IMG_3429

The complete bottom plate.451-10

When casing the movement, I notice that the central second hand slips on its tube. I very carefully solder the hand to the tube, as you can see above. A tiny amount of solder will do nicely.451-11That of course damaged the paint of the hand, and I order in some orange luminous paint.IMG_4136

Hand painted, and luminous compound in the tip re-applied.IMG_4145

Watch cased, waterproof tested, and ticking happily.


30 thoughts on “Repair + Service: Zentith El Primero Rainbow Flyback calibre 405Z

  1. I have a zenith rainbow flyback where it keeps perfect time but the chronograph functions dont work. I sent it to zenith and they told me to buy an entire new watch. A local jeweler told me it just needs one part but zenith doesnt sell parts. Any chance you could fix it?

  2. Hi Christian,

    I want to buy exactly this model for my collection, but now I am already doubt – is this Zenith calibre 405 problematic in general, or this one was just an exception? Would you recommend this watch or not really?
    One of the Rainbow Flyback I found is in mint condition and seller claim it runs at 270 degree with full wind, but no info about service (probably never serviced) ..

    • The
      El Primero is in many ways the watch industry version of a Ferrari. Technically advanced design (it was first out with loads of stuff), but also very delicate and somewhat fragile.
      Meticulous servicing on short intervals is key. If you intend to purchase something without a known service history, fine, but ship it straight for service and factor in some extra money for parts.
      I am a collector of chronographs, and as the El Primero holds an important position in the development of these, I would like to have one in my collection.
      If you are just looking for a durable “beater” chronograph then almost any other design would be the better choice.
      But then again, they do look nice?

      • I agree with that entirely. Good collection piece, but not for everyday wear. I just have a problem that the design was never revised to make the watch more reliable – they certainly have had enough time by now.
        At the moment, I have a 400Z in the workshop, on which the fourth wheel arbor is half eaten-up. Yes, that’s forcing 36,000 b.p.h. down the throat of that movement 😉
        If anyone has a spare fourth wheel, please let me know!

  3. Hello!

    I have a hard time getting a service kit, mainly gaskets for my elprimero flyback
    to sweden, the only way seems to be sending it to Zenith,
    do anyone here have any idea where to get parts?


  4. Christian
    I have the same watch with a ‘loose’ chrono minute register hand, hoping I can bag a slot soon !

  5. Pingback: Overhauling vintage Heuer 1553 S

  6. Hi Christian, what was your setup for soldering the hand back on the tube? Also how did you avoid getting solder in the tube :)? I have a similar issue and am looking for guidance. If anyone has a tutorial you could point me to that would be good to.Thanks.

    • Hi Adam,

      Put a tiny tiny amount of flux in the bend between the tube and the hand, and the tiniest amount of solder you are able to cut off. Press the solder into the flux.
      I am using an electronics soldering station. Warm up the iron, and press it gently on the hand next to the flux/solder and wait. The flux will melt, then the solder, and it will draw nicely in between the tube and the hand.
      If you don’t feel brave, I can of course solder the hand for you.

  7. Hmm, I have a Zenith EP 400 of similar vintage and like this has not yet had its first service.

    I have had a watchmaker do a quick visual check of mine with a lupe through the crystal back. He said it looked like it just came out of the factory. No dirt, snappy date change, no winding issues, accurate timekeeping etc.

    I am at a loss as to explain why this model is in such a poor state.

  8. Hi Christian,
    Interesting. Zenith El Primero chronograph is not cheap watch, probably cost the owner £6000 or above. The winding ratchet wheel is worn after 7 years, you now may start to think the movement is not made to high manufacturing specification. You can buy a small car for that price. Either the owner winds the watch every hour, which is not possible, one start to wonder why we pay so much for a branded watch, and is the manufacturer cutting corners? Are we all stupidly paying for the brand, more go to advertisement, I suppose, rather than the so-advertised precision piece? Food for thought ;-( . Should we stick to time-proven reputable vintage pieces, or rather paying so much for a piece of brick for today watches. What do all of he think?

    • Honestly… I would find it hard to justify spending that kind of money on a watch that remained pristine even after 10 years of operation.

      I much prefer vintage watches to (most) modern offerings anyway, and these can often be purchased for very little money. This Zenith I suspect I like because it looks like it might have been made in the 70s 😉

    • The owner just told me that it’s actually 10 years old. Still… I suspect the watch has been subject to a lot of vibration, which might have caused the rotor to go mad, but even then, you wouldn’t expect that sort of damage.

      Maybe they had a faulty batch of parts?

      • I was wondering if they had a metallurgical malfunction… or lubrication lapse? Would / should the teeth of that pinion have been greased?

        • No, you never lubricate pinion and wheel teeth. I think it only engaged with the upper half of the teeth, as only that bit is worn away. Looks like it was sitting too low on its arbor, so it’s a manufacturing fault.

    • Wowsers.

      I would be gutted if such a premium watch with that cost was so much in need of repair. I would like to think that this watch had either had some serious load under vibration or this watch has been serviced poorly by somebody else, rather than think this is natural progression in it’s life cycle. Yeung, funny you should pose that question as I alluded to that thought to Christian relating to the cost of the Longines Oposition as opposed to the actual cost of the replacement quartz movement it needs. I think the watch was about £700? yet the movement is £80.

      But having read this thread I feel a lot better about my watch as I have a few thousand to play with.

      • Dear All,
        Agreed. As a rule, I am willing to part my money for a watch with WMV ratio (Watch/Movt value) of 3-4 the most, beyond that, one has to think seriously whether it is justified. A good quartz movement cost roughly £20-30, a ETA 2824 cost £130 or so, a Valjoux equivalent cost £300 thereabouts (Christian, correct me if I am wrong), not matter how premier the brand is. BTW, a generic chinese made automatic movement may cost less than £10 !!! Paying beyond, eeh,.. unless for the 18ct gold case, is it worth your good money?. As a guide, most case with gold plating only cost the manufacturer less than £10 ( today gold price, surprise!!! ) for the gold. We know that one gram of gold which cost £45 today price, if spread thin enough, it can cover a quarter of football field. One kilogram of pure gold ingot cost £45k, if you are paying so much for Rolex, make sure you are bringing back at least one kilogram watch case and strap weight made of 24ct gold strapped to your wrist. Something to think about 😉

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