Service + Repair: Zenith El Primero calibre 400

IMG_9120Another day, another Zenith… Parashkev from London sent this one in, and he complains that the auto winder doesn’t work, and he would like a new sapphire crystal.IMG_9122

The amplitude is too low, so the movement does definitely need a service.IMG_9124

With the customer saying that the auto winder doesn’t work, I already have an idea what to expect, and the little specs of dirt in the movement confirm my fears.IMG_9130

With the rotor removed, you can see the bits of abrasion all over the movement.IMG_9138

The bottom plate looks clean, and there shouldn’t be any problems.IMG_9139

Abrasion everywhere…IMG_9149

The chronograph layer is taken off, and I’m curious what I will see underneath. I have an idea …IMG_9153

That’s some serious abrasion here.IMG_9154

And here is the culprit. The ratchet wheel driving wheel has a shorn off pivot, so the wheel tilted, and ground into the plate.IMG_9155

If this were a fluke, I wouldn’t say anything. But this is not the first Zenith I’ve had in here with the same damage, and more often than not, these Zenith movements are subject to excessive wear. Too much power, too fast beating… I now understand why Rolex took this movement down to 8 b.p.s. when using it in the Daytona. IMG_9156


the mainspring is still very spritely, and I don’t change it on these movements, as there is enough grinding the movement to dust going on, anyway. It doesn’t need more power!IMG_9158

The dirt has spread throughout the top plate.IMG_9159

Now it’s time to turn around, and take apart the bottom plate.IMG_9164

All looks well here.IMG_9716

Having cleaned all the parts, I start putting the movement back together. The cleaned and oiled mainspring goes back into the barrel.IMG_9717

Then I put the balance jewels back in.IMG_9718

The gear train is back, and the new ratchet wheel winding wheel is in place. All nice and clean.IMG_9719


The base movement is beating again.IMG_9722

And looking great.IMG_9724

Now I can put the chronograph layer back on.IMG_9725

The chronograph bridge goes on, and I can adjust the depthing.IMG_9726

That done, I put the bottom plate back together.IMG_9727

The dial and hands go on.IMG_9728

And finally the rotor and a new case back gasket.IMG_9729

A last adjustment.IMG_9730And all is well again.


8 thoughts on “Service + Repair: Zenith El Primero calibre 400

  1. You are absolutely correct Christian, I’ve seen dozens of caliber 400 in the same condition as the one pictured, with rust like specs invading the complete movement (with the exception of under the dial).
    Rolex took the 400 and made an excellent quality movement, far much improved and reliable than the 400 (I call it 400, or “El Segundo”, as Seiko beat the consortium that manufactured the Zenith introducing the first automatic watch in the world.
    Curiously enough, you grab a 6139 that’s been working for 20 years without service, and with the exception of perhaps wear in the barrel bearing surfaces, the movement will be in almost as new condition after only a service.

  2. Pingback: Zenith El Primero calibre 400 excessive wear issues?

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  4. Interesting, this movement is often considered the finest automatic chronograph movement of all time – and it looks like it has a serious design flaw. Zenith El Primero fans will hear nothing said against it, but the fact that you have seen this issue before suggests a real problem with this movement Christian.

    • I’m curious to know what Christian recommends for owners of El Primeros to address the stresses placed upon the movement: a very strict and relatively short service interval so that any potential problems can be addressed before wear causes significant damage? Is Zenith/LVMH willing to admit a problem?

      • Yes, a short service interval will certainly help. If the gear train is kept lubricated on the high-torque side (barrel, winding wheels, centre wheel), the chances of damage are lower.
        I will certainly not raise the issue with Zenith, and I’m sure they won’t be too willing to admit anything. If you have your watch serviced with them, you will of course never know.

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