Service: Omega Seamaster “Bumper” calibre 351

Elliot sent his Bumper in as it isn’t keeping good time – so it’s time for a full service. The dial has seen better days, but I actually love it. The discolouration looks great, and gives the dial a bit of history. I’d leave is as well if it were mine.

As you all probably know by now, I love bumpers. I think it’s the back-and-forth noise of the hammer that does it for me.

The beat error isn’t too bad, but the amplitude is a bit low, and the image is a bit wavy and irregular – so it’s definitely time for a service.

With the auto winder bridge removed, you can see the two springs that dampen the shock of the hammer hitting the plate.

All taken apart. You can see that the watch still had its original mainspring, and it’s quite compressed, so needs replacing.

Thanks to Chris in Australia, I managed to buy 5 original mainsprings for the Bumper – and Elliot is the first customer to profit from this purchase.

I start off with the barrel and wheel train.

The core of the movement is back together, and it’s ticking.

Now I press the wheel that drives the second hand arbor onto the third wheel.

Dial and hands are back on.

That looks better. A nice, regular beat, a good amplitude, and the beat error is acceptable. I don’t want to risk any damage to the hairspring to make that smaller than 1.5ms. The risk of making things worse is higher than any tangible advantage you would get of lowering the beat error. 1.5ms is fine, and I will leave it that way.

Elliot sent a new crown with the watch, but it wasn’t marked, and just somewhere in the packaging. Now it’s somewhere in my bin, and I can’t find it. The good thing is that he bought two, and he is going to send over the other one so I can fit it. 😉

So a word of warning here: if you send me any parts with your watch, put them in a little plastic bag or cling film, and stick that to an A4 sheet of paper, and write on it “Here is the part I told you I would send”. That way, it won’t end up in the bin. Also, a sender on the parcel helps me to expect a watch with parts, rather than something unmarked.

6 thoughts on “Service: Omega Seamaster “Bumper” calibre 351

  1. yeah i would say its to do with metal fatigue. think about folding a thin strip of metal once. keeping it stored like that, then unfolding it years later.

    the working spring would be like repeatedly folding and unfolding the metal strip. Over time the elasticity would be lost. =)

  2. Wonder what happens to a dial to end up looking like the back of a Flounder. Is it a chemical reaction between the lacquer coating and the paint below? It shouldn’t be moisture as these Seamasters should have a good measure of water resistance.

    • A reaction between the lacquer and paint seems likely to me; I spray painted something not long ago with paint of one brand and and lacquered over the top with another brand and got a result not unlike that on the dial. Was somewhat annoying 😉

  3. Lovely work. Dumb question: mainsprings in watches wear out and become compressed, as you say. This happens over years. Now, you got hold of some NOS mainsprings, which are probably almost as old as this watch and have been tightly coiled all this time. Wouldn’t they be compressed as well?

    Warned you it was a dumb question. Thanks!

    • The one used in this watch is NOS, and performing very well indeed. I guess it’s the action of winding and unwinding that tires out the spring. Also, old type (blue) mainsprings wear out quite a bit over time, whereas the new type (silver coloured) lasts a lot longer.

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