Teardown + Service: Omega Bumper 28.10 RA SC PC 350

Tony from Newcastle sent me this lovely Omega Bumper. This is a true family watch. Tony’s grandfather bought the watch in 1946, and gave it to his son in 1966, who wore the watch until 2009. Now Tony has inherited the watch from his father. So we are in the third generation, and the watch is still going strong!

As the watch had stopped working, Tony put the movement in some lighter fluid and cleaned it until it started up again. Nothing too wrong with that, but it will now need some of the right oil in the right place, and taking apart. 

The hour hand had a bit of an accident as well, and the 7 o’clock marker had come loose and had been glued into place a bit wonky, with a bit too much glue. The crystal is scratched, so it’s time for a proper overhaul, and that’s why the watch is on my bench.

The timegrapher image isn’t too bad, apart from the poor amplitude, which points at some dirt still being somewhere in the movement. The lines are also a bit wavy, but it’s ticking!

The movement is copper electroplated, and the case is gold, with a nice brushed pattern on the inside of the back. You can see why it’s called a bumper – the two springs at the top take a hit from the hammer that is used to wind the watch. In one direction, a ratchet just clicks, and in the other, the hammer winds the watch. A very simple, yet effective automatic winder, which gives the watch a very distinctive sound. The hammer hitting the springs is quite audible, so you will know when you are holding one of these. A nice piece to have in a collection, as it’s the first evolutionary step to today’s auto winders that have a rotor winding in either direction.

With the winder bridge removed, you can see how the hammer (with the “OMEGA” engraved in it) engages with the teeth of the ratchet lever. The ratchet lever engages directly with the transmission wheel. Also note that the two hammer springs aren’t original. As they will be pretty impossible to get as a spare part, I will leave those as they will be fine functionally.

The movement comes out through the front of the case after removing the bezel and crystal. If you want to laugh at the soldering, I suggest you try this at home. It’s not such a bad job for a home repair, and it works. I will definitely send the old hands back with the watch, as somebody a couple of generations down might want to install the original hands –  including the one that was soldered by great-great-grandad!

Having removed the bezel, I take the crystal out as we want to replace it.

Case taken apart and movement in the movement holder

I start off by taking the balance out.

The close-up of the balance wheel shows a mark – 794 or 799. This could be from the factory. As parts didn’t all come out the same size, they were sorted into tolerance groups, and the movements where then assembled by parts of the same tolerance group. Some of the wheel also have scratch marks – the number of scratches determined the tolerance group.

If you click on this photo to enlarge it, you can see a tolerance group marking on the uppermost wheel at 8 o’clock – 4 scratches.

Wheel bridge removed. Time to have a closer look at some parts!

The escapement wheel – as fresh as a daisy – after 66 years of service!

The second hand pinion + pivot. Again, minimal wear and tear.

The crown and castle wheels. Again, very good condition, and surely good for another couple of generations of service!

The pallet fork. Again, in very good condition.

On this wheel, some of the copper plating has oxydized and come off. The main thing is that the wheel is fine and the pivot is undamaged. This will clean up nicely. Look at the amazing state the pivot is in.

Close-up of the 7 o’clock marker on the dial. You can see that it’s a bit offset, and that there is a lot of glue around it. We will take care of that later.

Only the centre wheel, barrel and crown and castle wheels are left.

Main spring and barrel

I turn the movement around and start working on the bottom plate.

Bottom plate cleared.

All parts cleaned, rinsed, dried and sorted ready for reassembly.

Main spring rewound and oiled.

With the barrel bridge in, the wheels are put into place ready for the wheel bridge.

As soon as the balance wheel goes in, the movement starts ticking (I have of course wound the main spring for that).

Time for the bottom plate. I put some grease in for the castle wheel.

Almost done with the movement.

If you look carefully, you can see that the case is a bit pushed in left of the pendant tube. As the hammer can still swing freely, I won’t do anything about that. All part of the history of this watch!

Time to turn my attention to that 7 o’clock marker. I take it off and clean it. There isn’t much I can do about the dial damage. I very lightly scrape some of the excess glue off, but doing any more than that would damage the dial more than do it good.

Marker glued back on. Not a perfect repair, but the next step up would have been a complete dial restoration. And that would be a shame, as you want to see the age and history of the watch rather than have something that looks perfectly new.

I give the case, bezel and back a quick polish.

The new crystal is fitted.

I have bought some new Dauphine style hands for the watch. Tony and I discussed what would be best, and as we can’t get anything that looks like the original hands, we decided on this style as it nicely counteracts the tapered shape of the hour markers.

The diameter of the new hands was a bit too small, so I widen the holes a tiny bit by running the bottom end of a drill with the right diameter through it. This widens the hands just enough to make them fit snugly.

The minute hand also needs a bit of bending at the tip, so that the second hand can sweep over it without touching it.

The amplitude has improved considerably! As the beat error is corrected by moving the collet, I will leave it at 1.4ms. The damage I could do weighed against the benefit of getting a bit better than 1.4 isn’t worth the risk. The movement is going at a steady pace, and all looks good.

The movement goes back into the case, and I put the winder mechanism back.

And yes, I’m quite pleased with the end result. The little mark on the dial at 8 o’clock is permanent, but this is not a new watch. It’s a piece of family history. I think it looks great!

The polished case back.

This was a lot of fun and very enjoyable. To me, a third generation family watch is a very precious thing – I have my father’s golden Rado watch, but that’s only in the second generation.

 

20 thoughts on “Teardown + Service: Omega Bumper 28.10 RA SC PC 350

  1. Hello.
    Hope you can answere this question.
    I can se from the pictures that this movement has a mainspring for an non automatic movement,but this one should have a mainspring for slipping mainspring barrel,isnt it correct.
    Ive just servicet a cal 351 with a mainspring for automatic movement.

      • Hello.
        When i zoomed in i could se it 🙂
        Im aware of this system,but didnt know this caliber had this system.
        So this could be the reason why the power reserve on my watch is so bad.
        When you order a mainspring from Omega,does the bridle include,or do i need to order complete barrel?
        Because the bridel was not in the barrel when i serviced it.

        • If you got an automatic mainspring with the right dimensions (1.00 x .10 x 260), your power reserve should be fine. Not sure what you are expecting, but I’d say anything between 24 and 30 hours is just fine.

  2. I have recently found in omega with this same movement online, but is missing one of the bumper Springs. You mentioned this is very hard to find. Does this mean I shouldn’t buy the watch? I understand it will run without the bumper spring, but will hit very hard on the one side. With this eventually damage the Watch? If I could find a bumper spring, how much would it cost?

  3. Thanks for your excellent article on the teardown of an Omega 28.10 ra sc pc. My father had virtually the exact same watch and I have just had a go at servicing it. My mainspring has a bridel on its end and so is different to the manual type mainspring in yours. Do you know which is correct? Also, are special tools needed to remove the third wheel from the lower bridge for the oscillating weight.
    Cheers …….. Des

    • If your mainspring has a bridle on it, it has and extra small spring inside the barrel that allows the mainspring to slip when the watch is fully wound. You either have that, or an automatic mainspring.
      Yes, Bergeon sells a special tool to remove those wheels for around £50.

  4. Thanks for the fascinating stories. I am particularly grateful for this post on the Omega Bumper 28.10 RA SC PC.

    I recently found my grandfather’s Omega which was a retirement gift on July 31 1947 (the caseback is engraved with the date). It had sat in my mother’s possessions since he died in 1987 and it ran fine on winding except that the second hand did not turn. I had it revitalised by a local watch repairer (cleaned and oiled, new crystal, second hand repaired) and it now runs fine and is worn every other week in the rotation.

    However, I was still curious what movement powered it! From various Omega serial number lists, I deduced it was made in 1945-46 and Chuck Maddox’s excellent database (http://www.chronomaddox.com/OmegaCaliberList.html) suggested it was likely to be a 28.10 RA SC PC. This was confirmed by your photographs, particularly with the balance removed showing the calibre engraved – the same can be seen under the balance wheel in photos of mine. So the puzzle is solved with many thanks to all involved!

    Other mysteries remain regarding marks inside the caseback. What do the numbers 2438-1 and 710 (etched above and below the Omega triangle) mean? 87/58/B is crudely scratched inside, presumably suggesting services in 1958 and 1987 – but what would the B stand for? I noticed B12-8-72 scratched into a Omega Bumper calibre 351 caseback you posted, so is “B” watch repairer code for something?

    Anyway, many thanks again for the wonderful work you do posting these repair notes and photos and thereby answering at least some of my questions.

    Cheers, Rory

    • The numbers 2438.1 on the case back are the case number of your omega watch. You will need these when ordering case parts.
      I hope this wee bit of information helps …… Des

  5. Great post and a nice restoration. I have a Wadsworth US cased bumper that has a bit of lume come loose under the crystal. How do I remove the bezel and crystal to clean it? I would like to leave the movement and dial in the case.

    Regards

    Pete

    • Hi Pete,

      As I don’t know that particular case, it’s hard to tell you how to get the crytal off. If it’s an acrylic crystal, you can removed it with a crystal lift available on eBay.
      I don’t recommend that, though. I always take the movement out before removing crystals or bezels, to avoid damage.

      Best regards,

      Christian

  6. Hi Christian,
    Thank you very much for posting this. It helped me remove the rotor & auto winding mechanism after a loose screw within the case jammed against the stem. Reassembled & running well! Mine is a 9000000 no.
    Best wishes,
    Ian

  7. Christian:

    I have a 1953 (?) Omega Automatic passed down a couple of generations. It runs quite fast (3 or more minutes a day), and hasn’t been cleaned in a few years. Otherwise in good shape. How do I get it to you?

    Thanks –

    Tim

  8. Wow! I would love to have the tools to do this. I just bought a 14K Omega Automatic 28.10 R.A. P.C. that has this exact same case. Like mine though, there is no case number on it. I’m thinking #2445. Would you know for sure what the case # is?

    • Hi Scott,

      I’m afraid I don’t know either! Also, I don’t really know when Omega started to introduce case numbers …. Google might be your best starting point here.

      Best regards,

      Christian

  9. Pingback: Where to Service Old Omega Automatic in CT

  10. OOooohh! I really love pic no 6, removing the crystal!

    Really enjoy your blog, great source for inspiration!

    //W

  11. Pingback: 1946 Omega Bumper - Teardown and Service

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