Seiko 5126-6010 JDM

The Seiko 5126-6010 is an unusual watch for a number of reasons. To begin with it’s a Japanese domestic market model which means exactly what it says, it was designed and produced for the Japanese domestic market! Seiko had some much funkier designs for their home market than they did for the rest of the world and this model featured is no exception with its cushion case, orange dial and inner rotating ring. The orange versions of these models remind me of Doxas Sharkhunter, probably no coincidence considering the original orange dialed Sharkhunter was introduced in the 1960’s and Seikos 5126-6010’s date from the late 1960’s. Another unusual feature of this watch is the calibre 5126 movement. It’s an automatic winding, 23 jewel, 19,800bph movement with a day date complication. These weren’t produced for very long and consequently you don’t see them very often these days. The movement architecture is quite a departure from what Seiko was utilising in their other calibres, notably there’s no pawl and transmission wheel autowind components, and the keyless work looks quite different too. This calibre has more in common with the Swiss method of using reverser wheels to convert the rotors movement into winding the mainspring. As you can see from the picture below this model was part of their “Sports” range, watches that were part of that range had their water resistance upped to 70m depth. Interestingly this model was also given the “5” designation. “Seiko 5” has these days become a symbol of their lower range value for money watches but when the “5” designation was introduced in the 1960’s it was a symbol of Seikos rugged, dependable and unique watches which was meant to represent 5 different selling points,  automatic winding, day and date displayed in a single window, water resistance, a recessed crown at the 4 o’clock position and a durable case and bracelet. It’s nice to see that this example still has it’s original signed “Razor” bracelet that’s sized for a European wrist.


The caseback reveals a horseshoe design caseback and a production date of May 1969. The easiest way to spot a sports Seiko from the 1960’s is that it will be designated Waterproof as opposed to Water Resistant.


A peep inside shows the calibre 5126 movement, due to the rotor design it has shades of the 52 series of movements used in the LordMatic and King Seikos of the period.


With the movement uncased you can see the dial and handset have survived the last 46 years in remarkable shape.


Below the dial you can see the day and date wheels. With these early day/date calibres there was only one language choice on the day wheel instead of the two used from the 1970’s onward.


Underneath the rings you can begin to see the architecture differences, the keyless work is completely different to any other Seiko calibre, not because the crown has to be pushed to advance the date (the 61 calibres use a push method of advance) but because the architecture of the components is totally different. You can see this isn’t a budget movement, the machining of the plate is very well executed.

With the components stripped it’s ready to be turned over to tackle the motion work.

This is where the biggest differences are apparant, there’s no pawl and transmission wheel used to convert the back and forth motion of the rotor into winding the mainspring. The top plate is again totally different to anything you’ll see on Seiko 4 and 6 series of movements.


With the autowind plate removed you can see some of the reverser assembly componenets below. The balance has also been removed in this shot.


Further into the stripdown you can see it has an indirect driven centre seconds and a centre wheel bridge instead of a cock. A bridge is secured by more than one screw, a cock by just the one if you were wondering! You can also see the black ring barrel cover here.


The movement was soon fully stripped and ready for cleaning and inspection.



Nothing untoward was found during inspection so the reassembly began with the mainspring and barrel.


The motion work coming together here.


Just the autowind components to go and this side is done.


The keyless work coming together.


Just the day wheel to befitted….


….and the dial and handset can go back on.


With the movement recased it’s ready for the caseback.


I often see the type of service inscription on the caseback below on JDM models, at first glance it doesn’t make much sense but when you understand the Japanese method of date expression it becomes clearer. The 49 in the inscription doesn’t represent a year in the Gregorion calendar but actually represents the 49th year of the Shōwa era. Although the Japanese Government started using the Gregorian calendar from the 9th November 1872, the population at large were a lot slower to adapt and in the sixties and seventies (and even occasionally today) it was common to see this method of date representation. The Shōwa era was presided over by Emperor Shōwa, known outside of Japan by his personal name Hirohito. He was the 124th Emperor of Japan and reigned from 1926 to 1989, therefore the 49th year of his reign equates to 1975. This means the last service inscription on this watch was on the 12th March 1975. We are now in 26th year of the of the Heisei era so if you know the approximate manufacture date of the inscription you’re trying to date it’s not too difficult to work out what it should be. The SKN would be the initials of the watchmaker or the company he worked for if it were a large organisation.


With the caseback fitted the service is finished and she looks lovely. I must say I’m a huge fan of these JDM Sports watches!




As I mentioned earlier it’s still paired with its original Seiko Sports “Razor” type bracelet which is worthy of a picture on its own.


And a final shot of it back together. Lovely!






  1. Seiko pieces are my favorite choice when it comes to diver’s watches.Their craftsmanship is so admirable, Seiko is among the few brands that can offer a high-quality watch at an affordable price. Interesting article,too!


  2. Hi do you have more pics pf that rebuild? I’am curre tly rebuilding mine and would like to see more pics if ever thanks. Good job by the was it looks awsome!!


      1. Oh ok thanks.. I’ve undone my in bits and pieces and wanted a reference to putting it back together but thanks! 🙂 yours is nice!

        Liked by 1 person

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