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Seiko 7S26A Complete Service Walkthrough

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Lawson
Lawson

Seiko 7S26A Complete Service   Background   I have a good friend, a brother in Christ Jesus, who I've known for many years.  He knows I've embarked on retraining myself for a new career in Watchma

Lawson
Lawson

Assembly   This is a very easy watch to re-assemble.  In fact I'd recommend the 7S26A to be the first Japanese Movement to practice on, because it's so beautifully and logically laid out.  The only

Geo
Geo

That's a well put together post and great illustrations. Anyone about to embark on servicing or repairing one of these will find it very helpful.

Posted Images

steven WRT Addict

steven

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Posted

It's quite common for Seiko 7S26 to have this off centred hair spring problem. I serviced a few 7S26 every week and once a while one came in with the same issue. I seldom see this problem in other makes.

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steven WRT Addict

steven

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I just manipulate the part near the hairspring stud. After that it will be fine again. I guess the cause is the user knock the watch too hard or drop it and the hairspring material is too soft to withstand the force.

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clockboy Distinguished Member

clockboy

Posted
Posted

I just manipulate the part near the hairspring stud. After that it will be fine again. I guess the cause is the user knock the watch too hard or drop it and the hairspring material is too soft to withstand the force.

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Interesting, I have had that few times not but not just with Seiko,s. The issue for me with Seiko,s is lack of amplitude. The best I get is around the 230 mark but I must say they run fine & keep good time. The next time I service a Seiko I will change the mainspring (if I can purchase one) just the see the difference achieved.

jdm Distinguished Member

jdm

Posted
Posted (edited)

Interesting, I have had that few times not but not just with Seiko,s. The issue for me with Seiko,s is lack of amplitude. The best I get is around the 230 mark but I must say they run fine & keep good time. The next time I service a Seiko I will change the mainspring (if I can purchase one) just the see the difference achieved.

 

In my experience related above I used a new MS but still facing poor amplitude. A good new 7S26 goes around 285 with peaks of 305, still with many beats off place.  I've also seen brand new NH36 not going above 230. 

Edited by jdm
steven WRT Addict

steven

Posted
Posted

I guess that's the reason why they used graphite-mixed lubricant for the mainspring.

During service, after the mainspring is taken out, place it on the table to see if it lies flat then it's still good. If it doesn't lie flat, then it will affect the amplitude.

I guess the softer material of the hairspring is also the culprit of lower amplitude for Seiko 7S26.

The ones I've serviced, range from 200 to 280 of amplitude depends on the condition of the movement.

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bobm12 Distinguished Member

bobm12

Posted
Posted

@Steven: Thank you Steven I'll try that next time...I have a couple of Seikos in need of TLC! :)

 

@jdm: That's interesting since I've always suspected Seiko springs in general were rather flimsy.

 

@CB: Good thought CB, if you come up with a successful substitution of a main spring, please, let us know.

 

Cheers,

 

Bob

jdm Distinguished Member

jdm

Posted
Posted

@jdm: That's interesting since I've always suspected Seiko springs in general were rather flimsy.

 

I've used a GR MS with p/n mentioned above. Seiko only provided the barrel complete, now not even that is available anymore.

bobm12 Distinguished Member

bobm12

Posted
Posted

Thank you jdm, and sorry I missed the part number in your previous post! Must be the old eyes playing tricks! :) I just ordered one from cousinsUK.

 

Cheers,

 

Bob

bobm12 Distinguished Member

bobm12

Posted
Posted

By the way, ofrei lists a whole bunch of mainsprings, but he uses the Denison equivalent. Cousins lists that main spring as: 0.95 x .11 x 400 x 10 Automatic Is there a way to convert the units?...and possibly, how to read this description. Thanks in advance.

 

Cheers,

 

Bob

jdm Distinguished Member

jdm

Posted
Posted

By the way, ofrei lists a whole bunch of mainsprings, but he uses the Denison equivalent. Cousins lists that main spring as: 0.95 x .11 x 400 x 10 Automatic Is there a way to convert the units?...and possibly, how to read this description. Thanks in advance.

 

Cheers,

 

Bob

.95 tall, .11 thick (strength), 400 long for a barrel diameter of 10. The 7S26 barrel size is actually 10.5 but it fitted fine anyway. Other people used a slightly different type which costs more almost to the point of making more convenient to order a new movement.

bobm12 Distinguished Member

bobm12

Posted
Posted

Thanks. I know what you mean, cousinsUK's prices are about US$10 while ofrei charges US$18 both without shipping...and there is not much difference on shipping costs. In the end, it is just a matter of how long it takes to get the parts, since both will be about the same cost. I wonder if the material in ofrei is a different (maybe better?) one as you pointed out.

JimInOz WRT Addict

JimInOz

Posted
Posted

I have noticed that Seiko hairsprings are very susceptible to variation/damage.

 

I'm currently engaged in practicing removal of hairsprings/roller tables and balance staffs from a pile of old balance assemblies.

 

I am very impressed with the "robustness" of some of the vintage hairsprings, even with my clumsy first attempts a number of the vintage hairsprings showed no sign of damage at all.

 

They don't make'em like they did in the old days ;-)

steven WRT Addict

steven

Posted
Posted

After servicing the 4R37 and initial adjustment to centralise the hairspring, put it on the timegrapher and the reading was...

85531c95df7fe9c140bbadf1920b3a92.jpg

What the heck happened! I remembered of not demagnetize it yet so I zap it with an instantaneous demagnetizer. Instantaneous demagnetizer is wonderful, fast and easy. The immediate result is...

eedc2ea0e7513d444d0a082c7462de65.jpg

Manipulated the hairspring again and again and again and finally got it right.

4f844c76369c20e9848c652cc6242d6f.jpg

I'll call it a day now, tomorrow will case it.

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steven WRT Addict

steven

Posted
Posted

Thanks, Bob. Cheers to that.

You got a pic of the demagnetizer ?

I don't have a pic at hand now but found one the same from eBay.

8d639d6d01bc1e23f7cb14fda704d5f3.jpg

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jdm Distinguished Member

jdm

Posted
Posted

Finally some results. I have selected the balance that gives the best results and got the following. Amplitude is still not great, it's not a champion of isochronism across positions, but I'm happy with the regularity. Will finish assembly and recase to finally be able wear a watch that I've took apart and made work again :)

I've learned a lot in the process and got a couple of ideas to improve these service guides, I hope to be able to post my own soon.

 

post-1542-0-40297500-1449943570_thumb.jp

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