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Full repair of a Seiko 4206A for my mother! Commented video included

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Hi Watch bangers!

I did actually make it a personal goal of mine to present a watch every week but real-life caught up and ive been busy helping people move around haha. Bit nevertheless I am a week late but have another beautifull watch and project report for you guys!

This watch was one of a few which I presented my Mother for her birthday to let her decide which one I should fix for her. She chose this vintage Seiko 4206A which I got from Ebay and so I sat down and got to work.  Now I bought this watch online because I was really surprised at the remaining quality of the original dials and how there where still so many of them. After purchasing one and reading up a bit online it turned out that this movement line was particularly prone to behave irrationally or to repair so I kind of messe dup but nevertheless, I faced my challenge!

The watch on arrival:



1.       Remove the watch case by unscrewing the back and removing the stem


2.       Remove the Watch hands


3.       Release the Dial feet from the back with the small levelr at the 10 and the 4 Position I think and remove the dial.

As you can see it is in pretty good condition and has a very pretty sunbust effect. There is a slight stain though around the “ Automatic” text which left me kind of clueless since it is a metal surface and I wouldn’t really know what would stain it in such a way. I decided to leave it be to minimize the risk of further damage. Heres a close up picture:


4.       Remove the Day clip and the Day wheel underneath it. This revealed a very interesting sping-like swan neck system for the day-wheel quick set system. Never seen that before!


5.       Then remove the Day wheel spring and the 24 Hour day turning wheel.


6.       Now you can unscrew and remove the main setting cover plate and the attached date wheel.


7.       Take away the ( im not sure what this part really is called) but it is part of the quick set system which hooks into the second clutch wheel.


8.       Now remove the Date Spring and lever, the bottom day wheel and the hour wheel to remove some more from the front side.


9.       Remove the one translation wheel and the setting system sub cover which also separated the two clutches.


10.   And finally take out the clitches and the yoke, setting system to completely disassembly the front side. Now you can turn the movement so we can work further on the back side.


11.   Remove the Rotor


12.   Take off the Automatic module


13.   Remove the Winding wheel Y ratchet. I did try to remove the winding wheel in the first run but for some reason the screw did not watch to budge so I left it in for the picture. Off camera however I eventually did make.


14.   Remove the elegant arching balance wheel. I was really surprised to see this in this kind of movement since I thought that this kind of design was only present in really high end watches. Interestingly enough the 4206 B however has the classical one winged balance.


15.   Remove the Pallet fork system ( sorry for the blurry focus)


16.   Take off the main bridge and and the small spring attached to one of the screws.


17.   Pick out the Barrel, its ratchet and the 4th and 5th wheel. Interestingly enough the gears wheels have as many holes in them as the number which is kind of cool!


18.   Now focus on the little winding module on the bottom right. Remove the translation wheel, the spring and the small bridge to take it out completely.


19.   Almost done! Take of the final bridge which holds down the 6th wheel and the escapement.


20.   And finally remove the 6th wheel and the escapement wheel. With that, we have completed the disassembly of the Seiko 4206A.



For cleaning im still sticking to the good old hand cleaning method. So this means that I let the individual parts marinade in lighter fuel for a while before giving them a scrub and rinsing them of in Isopropanal alcohol. I was thinking about dipping my toes into the ultrasonic cleaning branch but im unsure what fluids to buy and what parts I cannot drop into the cleaner so I think ill stay with what works at the moment. Additionally im broke haha.

Mainspring service

Now as always I did not have a spare Mainspring at hand so I removed the spring by hand and checked it out:


As you can see it is / was absolutely disgusting haha so I gave It a good rub down in lighter fluid and isopropanol and the paper used for that was absolutely nasty in the end, see for yourself:


However, I did clean it nicely I think and lubricated the spring with Moebius 8200 and the barrel wit Moebius 8217 before winding the spring back in carefully. After closing the barrel I did a mainspring wind test with the winding wheel and it had tension on it so it seems like I did a decent enough job.


Moebius 9010 – All jewels aside from the pallet fork jewel pivots

Moebius HP 1300 – For parts which turn a bit slower. Between the arbour and the watches wheel, the barrel pivot in the main bridge or the metal pivots for translation wheels for example. But that’s just my personal tase

Moebius 8200 – Used to lubricate the mainspring

Moebius 8217 – Braking grease for automatic barrel wall

Moebius 9415 – For the tip of the pallet fork jewels.

Molycote DX Paste – Any strong friction contact points. So the setting and winding system basically


For the reassembly of course you just follow the above given steps and pictures from the disassembly backwards. Ive been thinking about making reassembly pictures as well, it would make the report way more comprehensive and would show more difficult nifty parts for example shock and balance jewel lubrication. However it would be way more annoying to take the pictures and it would cost me a lot more time. What do you all think?

Timegrapher Test

Okey, so once I’ve cleaned everything it was time to put my work to the test and I strapped the watch into the timegrapher. And this is the catastrophic result:


This was the start of the snowstorm like reading which followed. It couldn’t really pick anything up and I was just devastated. Because I did not have any replacement balance on hand, I was desperate and opted to measuring the Rate my eye and stop watch. As you can think, this did not end up well so I ordered a lot of a few spare movement to butcher them for the balance.


After placing in the 4th replacement balance however, I managed to get a decent reading. The Amplitide could be better, but this is the way I left it in the end haha.

Final Results:

After the timegrapher drama I closed the back up and attached a basic rubber strap for testing purposes. And from here on its basically B-Roll pictures! Here is a comparison of the movements size to my pinkie finger!

And here the final satisfying shot:



So yeah all in all a stressful but also fun little project which I could conclude by gifting the watch to my mother. I was very surprised to see the winged balance as well as challenged by working on a movement of this size but in the end I managed!  I hope you all enjoyed reading this and that the guide may help other hobbysts or even professionals ( haha who am I kidding) in the future. Any comments, questions or criticism is of course welcome!

If you guys would like the full commentated 4K Macro video of the whole process, ive uploaded it to my Youtube channel here and it would bring me great joy if you would watch it!

And so as always watch bangers...

Stay safe and healthy and till next time!




Edited by berlintime
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On 6/25/2022 at 5:10 PM, berlintime said:

I was thinking about dipping my toes into the ultrasonic cleaning branch but im unsure what fluids to buy and what parts I cannot drop into the cleaner so I think ill stay with what works at the moment. Additionally im broke haha

hi Ein Berliner

although i still wash/brush parts by hand in naphtha(lighter fluid) for really detailed stuff, you can go ultrasonic using the very same you're using now-lighter fluid and IPA. you can buy a home jewelry ultrasonic cleaner for $30 and I've seen them for less. they work just as good as the spendy industrial ones and if the nodes eventually do go out it won't break the bank to replace it. I've had my little machine for over two years now and it's still going strong. Lighter fluid won't hurt the shellac on pallet fork jewels or impulse pins and although IPA will dissolve or soften this shellac over time, like if you soaked them in it, it will not likely hurt it with a short dip/brush and dry to remove any residual lighter fluid. use your puffer or a hair dryer on low to evaporate any IPA that might be left. Don't blow on it though-the moisture in your lungs will surely get on your parts and you know where that leads...the last and most important part of ultrasonic is put your parts and lighter fluid in a small jar, THEN put that jar into your ultrasonic machine THEN  put water(I use deionized water) into your machine reservoir. Same with IPA. Do NOT put chemicals directly into your machine otherwise you'll have a bad day. last but not least, don't put the little jars directly on the bottom of your tank. try to suspend them just above that surface. Most of the DIY machines come with a hanging rack or basket just for that purpose. otherwise it'll wear your machine out very quickly.  This has worked for me and even though I have a large industrial watch parts washer, I use my little jewelers tub 98% of the time. If the parts don't come out to your satisfaction, just run them again. sometimes heavier crudded parts do need a 2nd run anyway. 

watched your vid-very good! big Seiko fan here. 


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  • 2 months later...

Great walkthrough! I think you would have got a much better amplitude if you replaced the mainspring and a better power reserve. I know some Seiko purists like to keep original mainsprings, which is fair enough.

I'd love to see some more walkthrough's in the future, as you clearly have a knack for presenting it in a clear way. Nice!

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