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Seiko 7000a manual wind mainspring query

Dan Mace

Registered User
Mar 31, 2020
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Hi all, I've recently managed to pick up a Seiko 7000-8000 with a 7000a manual wind movement, unfortunately the mainspring is missing. I would imagine the previous owner had the same trouble I've had with finding a replacement.

The only springs I can find online are for the automatic 7000 movement, would one of these be suitable? I've never used an automatic mainspring in a manual wind movement and don't think I've even heard of one being used.

If it won't be suitable, would anyone know a part number or suitable replacement part?

I've attached a few pics to hopefully help.

Thanks in advance.

Dan

IMG_20211018_205522.jpg IMG_20211018_205625.jpg IMG_20211018_205637.jpg
 

Chris Radek

NAWCC Member
Apr 13, 2014
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You can't put an auto mainspring in a manual watch, because it will wind forever (at best) or ruin the step in the barrel wall that is supposed to hold the outer end of the correct spring (at worst).

I thought I had seen every Seiko but this one is new to me.

How annoying that someone took out the (broken?) spring. Here's how you improvise: Measure the barrel inside height (if you can't do it directly, measure outside height and subtract the bottom and lid thicknesses). If in doubt, round down. That's the easy part. (Would not be surprised if you find it's a 6, aka 1.5mm) I'd try a strength of 10 or 11 and whatever length fills the barrel correctly, probably about 12-14". It probably takes a swiss style mainspring (with the little hook on the end that catches the step in the wall). Check the barrel to make sure.

If it's too strong and gallops, go weaker, 11 or 12. If amplitude is too low when it's perfectly serviced, go one step stronger, but I definitely wouldn't go past 9, that seems plenty strong for this size of watch.

Maybe someone will have the right Seiko part number, but I'm not sure that will help you find a non-Seiko spring. These probably came as complete "sealed" barrels.
 
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Dan Mace

Registered User
Mar 31, 2020
40
7
8
40
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You can't put an auto mainspring in a manual watch, because it will wind forever (at best) or ruin the step in the barrel wall that is supposed to hold the outer end of the correct spring (at worst).

I thought I had seen every Seiko but this one is new to me.

How annoying that someone took out the (broken?) spring. Here's how you improvise: Measure the barrel inside height (if you can't do it directly, measure outside height and subtract the bottom and lid thicknesses). If in doubt, round down. That's the easy part. (Would not be surprised if you find it's a 6, aka 1.5mm) I'd try a strength of 10 or 11 and whatever length fills the barrel correctly, probably about 12-14". It probably takes a swiss style mainspring (with the little hook on the end that catches the step in the wall). Check the barrel to make sure.

If it's too strong and gallops, go weaker, 11 or 12. If amplitude is too low when it's perfectly serviced, go one step stronger, but I definitely wouldn't go past 9, that seems plenty strong for this size of watch.

Maybe someone will have the right Seiko part number, but I'm not sure that will help you find a non-Seiko spring. These probably came as complete "sealed" barrels.
The barrel is the type with the thin seam you can open with a scalpel. I'll have to break out the calipers tomorrow, but hopefully someone can shine some light on the right part number as I could do without buying multiple springs, my better half has been tightening the purse strings.

Thanks for the response
 

Al J

Registered User
Jul 21, 2009
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Hi all, I've recently managed to pick up a Seiko 7000-8000 with a 7000a manual wind movement, unfortunately the mainspring is missing. I would imagine the previous owner had the same trouble I've had with finding a replacement.

The only springs I can find online are for the automatic 7000 movement, would one of these be suitable? I've never used an automatic mainspring in a manual wind movement and don't think I've even heard of one being used.

If it won't be suitable, would anyone know a part number or suitable replacement part?

I've attached a few pics to hopefully help.

Thanks in advance.

Dan

View attachment 676981 View attachment 676982 View attachment 676983
If you can find out the dimensions of the 7000 automatic mainspring, I would start by buying a manual wind mainspring of the same dimensions as a start.

Looking on the Cousins site, they call out the automatic spring as follows:

0.95 x .11 x 400 x 10 Automatic GR2377X

So find a manual winding spring of the same dimensions and see how that goes.

Cheers, Al
 
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roughbarked

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Dec 2, 2016
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The mainspring has a 45 hour power reserve.

and this is a rough guess.
Based on the 1972 parts interchangeability book. (which does not include the Cal. 7000 because it is from 1973).
However, the number for mainspring(Seiko) is 401.
The following number 401-700 could well be the mainspring part number. Don't quote me on it as it is an educated guess.
ie: mainspring number for Cal. 760,761,7622... is; 401-760

However, the mainspring number 401-001 happens to be the part number for Cal. 7605, 7606, 7619, 7625, 820. These though are automatic, with slipper.

As Chris mentioned above, Height is everything. or almost everything. It is important to measure height, strength/thickness and length. It is also advisable to measure inner barrel diameter.
 
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Dan Mace

Registered User
Mar 31, 2020
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From measuring the barrel it's looking like it is exactly the same size as the automatic spring but would be a manual version.

Thanks for the assistance everyone.

I'm guessing the manual version would literally just be a barebones version of the 7000 automatic movement, definitely an oddball one.

Thanks again for the help.
 

Dan Mace

Registered User
Mar 31, 2020
40
7
8
40
Country
From measuring the barrel it's looking like it is exactly the same size as the automatic spring but would be a manual version.

Thanks for the assistance everyone.

I'm guessing the manual version would literally just be a barebones version of the 7000 automatic movement, definitely an oddball one.

Thanks again for the help.
Also, if anyone has a link to where I can get this spring, please let me know as I can't seem to find one
 

John Runciman

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Aug 13, 2003
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Looking on the Cousins site, they call out the automatic spring as follows:

0.95 x .11 x 400 x 10 Automatic GR2377X

So find a manual winding spring of the same dimensions and see how that goes.
the theory above sounds reasonable and would agree with anything I could find on the 7000 series that they're all similar. This would mean we could look in the mainspring catalog in the section by sizes and pick an equivalent spring that's not an automatic. but this is where our theory falls apart as this probably was not a common watch and they don't have a mainspring that's not an automatic of the correct length. The 400 mm length is what does us in as you can see everything of the correct length is for an automatic. I don't suppose you have access to spot welder? As it be easy to modify the end if you had one.

then how about a compromise like if we went dropped the with down a little bit and you really don't need all that running time do you? I'm attaching a second image in which case there's a couple of choices.

From measuring the barrel it's looking like it is exactly the same size as the automatic spring but would be a manual version.
I find sometimes my reading skills are lacking while it might seem nice to measure the barrel we looking for a mainspring? Do we have the measurements of the actual spring?

Seiko 7000 series mainspring problem.JPG Seiko 7000 mainspring compromise.JPG
 
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Dan Mace

Registered User
Mar 31, 2020
40
7
8
40
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the theory above sounds reasonable and would agree with anything I could find on the 7000 series that they're all similar. This would mean we could look in the mainspring catalog in the section by sizes and pick an equivalent spring that's not an automatic. but this is where our theory falls apart as this probably was not a common watch and they don't have a mainspring that's not an automatic of the correct length. The 400 mm length is what does us in as you can see everything of the correct length is for an automatic. I don't suppose you have access to spot welder? As it be easy to modify the end if you had one.

then how about a compromise like if we went dropped the with down a little bit and you really don't need all that running time do you? I'm attaching a second image in which case there's a couple of choices.


I find sometimes my reading skills are lacking while it might seem nice to measure the barrel we looking for a mainspring? Do we have the measurements of the actual spring?

View attachment 677250 View attachment 677251
Unfortunately it arrived without the spring, I'd imagine the previous owner had the same issue in trying to identify a spring. I'd happily accept a drop in running time as any running time would be better than what I have now.
 

Al J

Registered User
Jul 21, 2009
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the theory above sounds reasonable and would agree with anything I could find on the 7000 series that they're all similar. This would mean we could look in the mainspring catalog in the section by sizes and pick an equivalent spring that's not an automatic. but this is where our theory falls apart as this probably was not a common watch and they don't have a mainspring that's not an automatic of the correct length. The 400 mm length is what does us in as you can see everything of the correct length is for an automatic. I don't suppose you have access to spot welder? As it be easy to modify the end if you had one.
Don't really need a welder. The sliding bridle can be removed and the end modified to a tang by heating and folding it over.
 

John Runciman

NAWCC Fellow
NAWCC Member
Aug 13, 2003
531
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Seattle, WA
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The sliding bridle can be removed and the end modified to a tang by heating and folding it over.
yes that is one of the traditional ways to do it. Other times people make a rivet and attach the part that way but I think that works better in a pocket watch where you have lots of space. I'm wondering if we can modify the bridal? For instance it's already attached its nicely spot welded. What if we cut most of it off and just left a little tiny piece like you'd find on a conventional mainspring? I suppose would have to see it attached the end of the spring as to whether that's possible or not?
 

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