Service: Seiko 7S26-0200 Scuba Diver’s watch

IMG_7477It’s been a while since I have done something non-Omega related! This chunky Seiko Scuba Diver’s watch belongs to Torsten from Hong Kong, and it’s running 30 minutes per day fast! Looks like it needs a service …


Not very good – huge beat error, and a pretty random pattern.


Even though the dial doesn’t have a window for the day and date, the 7S26 has both. A bit odd – if it’s there, you might as well show it…IMG_7482

The finishes here to remind me of quartz movements, not quite what you expect from a mechanical movement.IMG_7485

The plastic case ring would suit a quartz watch better, too 😉IMG_7486

The auto-winder is the simplest construction possible. In order to save money, you can’t even hand-wind the movement.IMG_7487

I’m not the first one to take this movement apart, as you can see by the various scratches where people tried to remove the circlips for the auto-winder wheel. It’s very easy to remove without even touching the plate, so I wonder what’s been going on there.IMG_7488

The escape and fourth wheel both have cap jewels, but only at the top, and not at the bottom, which makes the whole exercise a bit pointless.IMG_7489

The click for the barrel wheel also isn’t the most expensive construction.IMG_7490

Where it matters, execution is good.IMG_7492 IMG_7494

I will fit a new mainspring as usual. I’m using a 0.95 x .12 x 400 x 10.5.IMG_7495

With the balance jewels removed, I’m almost there.IMG_7496

Ready for the cleaning machine.IMG_7497

All parts cleaned and ready for reassembly.IMG_7498

I start off by fitting the cap jewels for the escape and fourth wheel.IMG_7499

Then the new mainspring goes in.IMG_7500

The circlips for the auto-winder wheel is back in place.IMG_7501

And the great train goes back in. On some versions of this movement, Seiko didn’t even cut out the wheels, but this one has 3 spokes on the third and 4 spokes on the fourth wheel.IMG_7502

The wheels are turning freely and are oiled, and I can now put the pallet fork in.IMG_7504

The movement is beating again.IMG_7505

Now this looks a lot better than before!IMG_7506 Now all the plastic wheels for the day and date wheel are mounted.IMG_7507

The date wheel is working, and I’m ready for the day wheel.IMG_7508

All in place. Shame nobody will ever see the date and day change 😉IMG_7510

The dial and hands are in great shape. I just wonder why there is no “Seiko” on the dial…IMG_7511

The crown gets a new gasket.IMG_7512

And so does the screw back.IMG_7513

The case back has quite a bit of damage from corrosion.IMG_7516

The movement is cased again, and the watch looks great!


18 thoughts on “Service: Seiko 7S26-0200 Scuba Diver’s watch

  1. Hi, does the day wheel just prize off ? are there lugs on it to hold it on. I am just refurbishing a 009 and turning it into a 007, I need to take the day wheel off and put it on a replacement movement but don’t want to break anything.

  2. Hi Christian,

    What size Phillips screwdriver did you use to remove the Phillips screw holding the date plate?



  3. hello there, love your posts, very informative, with great photos.

    would you help me with a question? where do you get your mainsprings from? I have a 7002 diver whos mainspring broke, and i cannot find a replacement for it.

    could you please help?

    thank you

  4. It’s a SEIKO mod. Seems like he got the dial from Jake B. over @
    This is a BB (black bay) Tribute homage to the TUDOR.

  5. Christian, aren’t I right in saying the 7s26 was a cheaper (and later) made version of the 6309 and 7002 in that there are less parts so cheaper and quicker to manufacture?

  6. Immediately I saw the watch I recognised the homage to the new Tudor Heritage. It looks really nice (the Seiko, that is). I guess that the case and movement are actually quite old, judging by the corrosion on the screwed case back.

    I have several Seikos fitted with the 7S26, and could never understand the lack of a manual rewind facility for a movement, I understand, is designed for the western market. Economics I guess. Any Seiko fitted with a more elaborate movement appears prohibitively expensive in comparison.

    Many years ago I came across a review of a Seiko Monster, with a lot of time devoted to the 7S26 movement. So for anyone who hasn’t read this, here is the link

  7. Christian, As always a job well done. Thank you. Let me provide some background on the watch. I bought this 7S26 with its original dial, hands and bezel from one of the Ebay dealers based in the Philippines. To provide the basis for a Seiko “mod”. In this case a Tudor Heritage Black Bay homage with parts produces by Dagaz watches.( Above-mentioned parts were then replaced to create the homage.

    Hence the no date/day dial and lack of “Seiko” on the dial. There is a large market and fan base around these Seiko mods. With the Seiko 6309 model getting less and less available the modders are now using the SKX line with the 7S26 as a basis for mods.

    Check out Dagaz watches and Yobokies to get an idea for the variety of flavors out there.

    In any way there is a lesson learned here. Prices for used 7S26 Seikos are pretty stable and somewhat high. The cost of the watch, plus shipping, plus getting it fixed by a professional (which I am happy to pay) was actually higher than buying a new Seiko SKX on Amazon…

    So if you ever get into Seiko modding just buy a new watch as it will be cheaper at the end.

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