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Seiko 7S26

rattandsonwatchmakers
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rattandsonwatchmakers WRT Addict

rattandsonwatchmakers

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i need to replace a seiko 7S26 automatic movement...the watch is day/date....the movement shipped to me is a date only...seiko told me that this model number is available only in date and they make none with a day wheel....all well and good but my movement is stamped 7S26 and it has a day wheel...is this a complication added at time of installation with extra parts purchased...driving wheel and day wheel???...thanks....

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bobm12 Distinguished Member

bobm12

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Hi rattandson,

 

what is the new movement caliper (stamped on the rotor hopefully)?

 

I believe this movement is discontinued for sale in itself (7S26), although it can be had still in new production Seikos. Alternatively the discontinued 7S36 is completely interchangeable if you find a working one. Also a rebuilt 7S26 can be had from here: http://www.10watches.com/apps/webstore/products/category/347351?page=1.

 

I believe the 6R15 is the modern version of the above movements so it can be replaced -- hopefully directly -- but the price may be higher. It is a much improved movement that I think allows for manual winding and hacking.

 

If you have your old movement day/date in good working condition and cosmetics, you might be able to "transfer" those complications or the part(s) that you need to the new movement...and then again you might not depending of the answer to the original question above.

 

The original plastic gears for the 7S26 are available from cousinsUK (only, to my knowledge) those are particularly touchy and easily broken if not properly assembled. Also the retaining day c-clip tends to jump into nowhere if not treated carefully, it has an underside "dent" at 6, when the opening is at 3, for a small screwdriver to be inserted (removal procedure).

 

In any case, here is a helpful link that might be redundant in your case: http://www.clockmaker.com.au/diy_seiko_7s26/

 

Cheers

 

Bob

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Blacklab Distinguished Member

Blacklab

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Funny thing Bob, I was looking into this the other evening. There is also the NH35 (date), NH36 (day/date) & NE15 (not available until April 2015 from Cousins). All appear to be the same dimensions as the 6R15, however the 7S26 is 4.9mm high the others range from 5.25 to 5.32 high which may cause the second hand to foul the underside of the crystal. 

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bobm12 Distinguished Member

bobm12

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That is correct Blacklab,

 

I've never done the swap so I may be here getting into unknown waters, as I usually restore these movements (again never swap). Still, I believe I read about this issue and the fix was to swap the cannon pinion and/or just the hour wheel on the 6R15, now don't quote me on this one since it was a discussion on another forum. I'm hopping another member that has done the conversion will jump in and give his 2 cents.

 

From other websites I put together what I found related to this topic:

 

"More interweb digging... It appears that the NH35 shares a few parts with the NH25, which I understand shares some parts with the 7s2X series... it's getting interesting. It appears that both movements should share the same hour wheel and many of the keyless works bits as well. It really might be as simple as installing the day wheel and clip on the movement...."

 

"The good news first! You can put the 7s26 day wheel into the NH35A movement, essentially making it an NH36! You have to swap the hour wheel and the quickset cog and that's it!! It all works perfectly, everything clicks like it should, it sets perfectly! I thought I was about to have myself a hacking SKX009. Then, after it was all reassembled (no small feat in my current condition), I was excited to have my hacking SKX. As I went to insert the SKX stem (an integral unit with the crown), it all went pear shaped! The SKX stem is too large to fully insert into the SII movement. The interference is right on the main plate of the movement. A problem that can not be solved without either machining the stem or the movement... icon_e_sad.gif Needless to say, I am disappointed. Now I wonder if it's possible to take the hacking bits from the SII and put them into the 7s26 icon_neutral.gif That will have to wait for another day. I don't even think I can do the swap back right now... Having the leg down that long was not the best..."

 

"Pop the stem in to your dremel tool, break out a diamond file, and gently turn the stem down to fit... I had to do that operation to get one of my Rolex shoulderless spring bars to fit in the holes I drilled in ExploMaster. Worked well enough, but I had extra spring bars - how many stems do you have? Are they easy to get?"
 

"I haven't checked on the availability of stems. The SKX stems/crowns can easily be had from Jules Borel. 10watches used to have some aftermarket crowns, that I think took a threaded stem, but I haven't seen them on the site for a while. My only rub with turning down the stem, is that then the watch the 7s26 goes into has a stem that doesn't fit right. Stems are so small and made of such brittle material, I think it's really important to have them fitting just right if you want them to last."
 

And so, there we have it, it could be done!

 

Hope it helps,

 

Bob

 

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Blacklab Distinguished Member

Blacklab

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Same thing here Bob, I always try to repair rather than replace, however it does open up the possibility of buying a stripped out case & putting something reliable in it. Funnily, the same subject is being discussed on SCWF at the moment as well.

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