Seiko SKX Hack and Wind mod (7S26 replaced with NH36 or 4R36 movement)

I have been meaning to write about this interesting mod on my blog for a while. However having been rather short of time lately I keep deferring it… following a recent thread on the forum I thought I would post some info on here.

The mod is applicable to SXK007 or SKX009 watches. It consists in the replacement of the original 7S26 movement with a “modern” Seiko Calibre 4R36 or Hattori NH36, which have a hack and wind facility.

The thing to bear in mind is that there are two issues to get around with this mod:
1- The stem will be different on the new replacement movement, and the original SKX crown/ stem cannot be disassembled. To work around this, I use the crown and stem from a SARB059 watch, it is the perfect fit with the SKX and also looks great.
2- The day disc and date wheel in the replacement movement will be positioned for a watch with crown at 3 o’clock, so will not align with the aperture in the dial of the SKX. The easiest way to get around this is to remove the original day and date wheels from the 7S26 and fit them to the new movement.

I really like this mod, it makes for a perfect watch. I ended up carrying this out on my own watch. I tend to wear my watches in rotation, only for a day or so. Therefore the ability to give the SKX a wind before I start wearing it means I know I will get good timekeeping straight away, as I do not have to overcome the initial low state of wind.


Here are a couple of pics of the mod:
Starting with the SKX:
https://www.dropbox.com/s/e56zuh39my...4415.jpg?raw=1

Caseback open, revealing the 7S26 movement.
https://www.dropbox.com/s/t8r4hfh8nc...4506.jpg?raw=1

Dial, hands and date wheel/ day disc are off, ready to be swapped.
https://www.dropbox.com/s/wua5rb7ksh...5249.jpg?raw=1

Hattori NH36 movement, will need to be fitted with the original day disc and date wheel.
https://www.dropbox.com/s/rb33t1iw7l...5326.jpg?raw=1

After assembly gasket is cleaned and lubricated with silicon grease.
https://www.dropbox.com/s/dnv39574pb...2435.jpg?raw=1

A view of the SARB crown, I think it looks great on the SKX.
https://www.dropbox.com/s/pfc18xvreh...2654.jpg?raw=1


This is how the movement performs out of the factory, not too bad at all (note in reality the amplitude is a little bit higher than displayed, as I have not set the timegrapher to the actual lift angle)
https://www.dropbox.com/s/19hkd0r6f9...1624.jpg?raw=1


It can be improved with some adjustment.
https://www.dropbox.com/s/pfnes4t5ok...2303.jpg?raw=1

And I finish with a pressure test.
https://www.dropbox.com/s/rnty9qan3l...5801.jpg?raw=1

Interesting to see that the beat error's wrong prior to adjustment, typical of these movements!

Where are the replacement crowns sourced?

Hi Paul
I buy them on ebay, p/n 1E70D1SNS0. Supply can be an issue, sometimes they are just nowhere to be found!

And yes as you said quite typical performance on these movements. I find that the variance between horizontal and vertical positions can also be improved usually with adjustment of the hairspring between the curb pins. The movement is fitted with an etachron type system so it makes things much easier!

I`ve had one on the bench to play around with and I remember the etachron-style adjuster...........rather annoyed to find that my etachron key didn`t fit!

Good write up thanks.

I had this done to my SKX011 when after 20 years it required a service. The service option was not on the cards due to cost so I looked to replace the movement and the hacking option seemed sensible.

It makes an excellent watch so much better.

Yes it is less labour intensive than a service, so the movement swap provides a good alternative, with a little improvement in functionality along the way...

Enjoyed that thanks Olli. I've been intrigued by that swap since reading about it a few years back (on here perhaps...).
Is a 6R15 also a potential swap? I know there is some commonality between 7S26/4R36 and 6R15, to what extent, I have no idea!

I have never done it, but I believe it has been done and would not take much more effort.
The 6R15 is a date only movement, so there would be a few more parts required from the 7S26 to make it work.

I also had this done to my SKX009, a watchmaker fitted a NE15 movement, the SARB crown and a sapphire crystal to really give the watch an upgrade and a new lease of life.
Thanks for sharing your work!


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I’ve just got my SKX007 back from Olli after the NH36 and SARB059 crown mod and a pressure test, and I’m just bumping this thread to say how impressed I am with Olli’s work and with his customer service.

I highly recommend this hacking and hand-winding mod if you have an SKX007, and I highly recommend Olli if you need work doing.

What happens with regards to the screw down crown?

I did the same mod recently. There was an SKX on SC that had been withdrawn due to needing a service so a perfect candidate. Here's the sellers pic -

https://farm8.staticflickr.com/7888/...a35c8f7c_b.jpg

Aside from the 4R36 movement and SARB059 crown and stem I wanted to make a couple of other changes. I had spare white on black day and date wheels and ordered a domed sapphire from Crystaltimes -

https://farm8.staticflickr.com/7834/...b2dccbdd_b.jpg

The movement arrived from Cousins without the movement ring and date wheel so these parts had to be removed from the original 7S26 -

https://farm8.staticflickr.com/7816/...ddf5b1f1_b.jpg

New movement as it arrived -

https://farm8.staticflickr.com/7892/...875c5e57_b.jpg

And after a slight tweak -

https://farm8.staticflickr.com/7905/...62ee634b_b.jpg

There are aftermarket crowns with screw in stems that will work and are also a bit cheaper, but I like to use Seiko parts where possible. The SARB crown is also engraved, which is nice -

https://farm8.staticflickr.com/7865/...07b4e914_b.jpg

You'll also notice I drilled the lugs for easier bracelet changes. It's hard enough swapping straps and bracelets with the shoulderless Seiko springbars and almost impossible when you have a bracelet with tight fitting solid end links so this mod was essential imo.

The new sapphire is slightly different from others in that it has a stepped edge for a flush fit with the insert rather than the usual beveled edge which creates a halo effect around the edge -

https://farm8.staticflickr.com/7837/...b25db715_b.jpg

I notice from the above pic it's exactly two weeks since I fitted the new movement and in that time it's lost 3s vs my atomic G. Pretty good but more of a fluke as it's very tricky adjusting these movements to a perfect 0s/d.

Two last pics, one on an Erikas MN strap and one on the Strapcode Jubilee it came with -

https://farm8.staticflickr.com/7812/...093cd11a_b.jpg

https://farm8.staticflickr.com/7812/...7402ac4a_b.jpg

To answer my own question, the 059 crown is also screw down so this looks like a pretty good upgrade.

If it’s not too rude? What sort of costs are we looking at?

Quote:

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Originally Posted by IAmATeaf

To answer my own question, the 059 crown is also screw down so this looks like a pretty good upgrade.

If it’s not too rude? What sort of costs are we looking at?

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The crown was around £28 from eBay and the movement was £75 after vat and postage from Cousins.

Cheers

Great mod!

my fave seiko diver is the stargate mark 1 SKZ327 i'm sat wondering if a 6r15 could be dropped in. that and a sapphire and i'd be over the moon!

Great mod!
(As for me, I sold my SKX and bought a turtle...)

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Nice! Where do you usually pick up your white-on-black day/date wheels?

I've got three 7S26 projects going on at home right now, waiting for parts...thought about swapping at least one to 4R but figured I'd just wait until they die.

What is the price diffence in swapping in 6R15 instead 4R36?

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Quote:

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Originally Posted by ktmog6uk

my fave seiko diver is the stargate mark 1 SKZ327 i'm sat wondering if a 6r15 could be dropped in. that and a sapphire and i'd be over the moon!

---

One of many sapphire options here. https://crystaltimes.net/shop/all/modern-divers/ct068/
And yes, the 6r will work, but you'd need to add the day parts as its date only.

Didnt realize the day/date and day difference. When I think about it, my SARG001 has a day only...
Tnx

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