Reassembly: Omega Seamaster Automatic DayDate 1660264 calibre 1020

Now I’ve got a new mainspring and back gasket for Constantine’s Seamaster, I can put the watch back together again.

As usual, I start by pegging out all the jewel holes and manually cleaning the parts to get rid of all the baked-in dirt.

Then the parts go into cleaning fluid, then the rinse, and then they are dried.

Everything lined up and ready for reassembly.

The new mainspring goes into the barrel and is lubricated.

The barrel and barrel bridge are mounted.

Now I put the wheels of the gear train in, ready to put the wheel bridge in.

The wheel bridge is screwed into place, and the pallet fork and pallet bridge are mounted.

The balance wheel with the hairspring and the balance cock are cleaned separately to avoid damage to the hairspring. I oil the top jewel before putting the balance back on the cock.

I drop the balance and put the cock into place. As I have wound the watch beforehand, the balance starts to swing immediately.

Not bad for just assembled. The random dots that appear come from the movement being in the movement holder, which is put into the timegrapher, so there are some additional vibrations. They will disappear once the movement is properly cased.

I turn the movement around and put the winding and setting gear in. I have cleaned up the very rusty pull-out piece as well as I could, but I don’t want to take off too much material. If I would have gone for a highly-polished finish, it would have gotten too thin. I’d rather have the function than the beauty 😉

The hour and minute wheel and the date wheel go in, and I’m ready to put the date ring in.

Date wheel and plate in, next the day wheel and the dial.

The dial gets a final brush.

Now I press the hands on, making sure they are all parallel and don’t touch.

Before putting the auto-winder in, I put the movement into the case.

The auto-winder gear is put together.

And the movement is complete.

I couldn’t find the original Omega gasket, but Cousins sell a generic one that is very much the same size and material.


The watch back has to be put back in with a press as the gasket needs considerable power to be put into place.

Back to its old glory.

The case isn’t entirely to my taste, but this is a great movement. Lovely watch!


29 thoughts on “Reassembly: Omega Seamaster Automatic DayDate 1660264 calibre 1020

  1. Hi I desperately need an advice. I just serviced this same movement. Among the other broken parts there also was the second pinion. Now I purchased the Omega 1020 7217 H1 part but it’s not long enogh and remains under the height of the minute wheel barrel making it impossible to fit the second hand. Do you know if there is a longer version of the pinion? Am I missing something else? Thank you so much for help!!!

  2. Hi,

    Loved your story on this, thank you for sharing. I have just purchased an Omega 1020 cal watch, really looking forward to getting it, nice to know a little more about it.

  3. My dads old 1020 has been in a drawer for years Id love to get it going. I have got all the kit to do it. Do you have a video of tear down and rebuild?
    Cheers Regards Steve

  4. And before I get to disassemble my watch….
    The problem is lately it’s always getting slower like 5 minutes each day after the day date change in the middle of the night….
    What should be the problem? Is cleaning the whole things and changing the mainspring is enough or did I missed some parts to replace with? Thanks

    • I can’t really tell without having the movement in my hands … Service it, and then see what it does. If you are afraid to remove the wheel over the third wheel (and you don’t have the Presto tool to remove it), just leave it on.

  5. Hey man,

    I want to disassemble this similar calibre (1021) but worried about the pinion that held the third wheel…. Did you take it off?

  6. what year do you think this watch is that you referbished, im looking at one that is the exact same, with out the Sea master script on the dial and the case back does NOT have the sea monster but it has the omega text on the inside?

  7. hi, I got an omega seamaster with the 1020 movement that I bought off of ebay. how much do you charge to service it like you did in this article. thanks, rob

  8. I cannot press my omega case back on, is it supposed to click into position or is it held by the gasket

    Thanks Garry

      • The original Omega gasket ring has 2 asymetrical lip side. (one is square, one is slightly rounded) I assume there is a correct orientation when placing the gasket.

        Do you place the gasket squared side down in the case on the movement holder, and rounded side up to facilitate of the bare case cover?

        Or the other way around. Place the gasket square side on the case cover and push it in the case?

        • I place the gasket on the case back, with the rounded side facing the case, and then press the case back into the case, using a bit of silicone grease to facilitate the process.

  9. Hi just bought and Omega with this movement. To change day, you have to move the hands anti-clockwise, not clockwise. Does this mean it’s not right?

  10. Hi Can I ask how to adjust the day calendar? I’ve just got a Seamaster 1020. It works perfect but the Day calendar does not rotate and I don’t know how to set the Day. Thanks.

    • Hi Li,

      The crown has three positions: pushed in, just for winding
      out to the first stop: change day
      out to the second stop: anti-clockwise: set time
      clockwise: set time back, set day forward

      If that doesn’t work, something is wrong.



  11. hi there, I just want to know where do I buy that red gasket in the last picture before you close up, because I have an omega seamaster cal.1020 the back keep falling out and I cannot press it back – now I think that red O ring gasket will do the trick please tell me where to buy it and how much include shipping thanks

  12. Looks great.

    By the way, I like the dial but am not very fond of the case either. I don’t like the squared off top and bottom and the gold color or plating, which will no doubt continue to flake off. I wish the entire case and back were stainless steel and the top/bottom rounded off. But it’s a nice watch and you’ve done your usual great job with it.

    For some reason I’m not crazy about a lot of Omega cases and dials but appreciate their history and movements.

    Thanks very much.

    • I completely serviced my 1020 but it won’t auto wind. Runs spot on manually winding. What might the issue be, the rotor turns freely

  13. Pingback: Teardown Omega Seamster Automatic Day/Date calibre 1020

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.