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Seiko 7006a Mainspring size

Tmuir

By Tmuir
in Watch Repairs Help & Advice

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Tmuir Distinguished Member

Tmuir

Posted
Posted

I've just stripped down a Seiko 7006a which looks to me to have the wrong size mainspring in the barrel.

I understand that Seiko only sold the barrel with mainspring as one unit and it is now unavailable, but was wondering if anyone knows the size of a suitable replacement mainspring as I can't find the spring dimensions anywhere.

Worst case I can work it out, but would be nice to know if there is an already accepted size replacement spring.

Here is a photo of the spring in the barrel, it looks to be taking close to 50% of the space within the barrel, which makes me think its too long.

Is it just me that thinks the spring is occupying too much space within the barrel?

 

mainspring.jpg

jdm Distinguished Member

jdm

Posted
Posted (edited)
39 minutes ago, ro63rto said:

Seiko never sold just mainsprings.
The part number you need is
201024 shared by the 7005, 7009 and probably a few more.

The problem is that barrel complete for these old watches are not supplied anymore, so one has to use NOS (if any can be found), or reuse from another mov.t. Of corse the MS can be measured, I suspect i's the same size as on the 7S / 4R series.

Anyway to me it seems there is nothing wrong with that MS, and I would be cautious before blaming it. An approximate judgment on its health can be had observing the shape it takes when uncompressed.

Edited by jdm
Chopin Super WRT Addict

Chopin

Posted
Posted
44 minutes ago, ro63rto said:

Seiko never sold just mainsprings.

The part number you need is

201024 shared by the 7005, 7009 and probably a few more.

 

 

It fits these ones below.

7001A
7005A
7006A
7009A
7019A
7025A

Could you first try and put it all together and see how it functions ? As has been said maybe you shouldn't consider it the wrong part just yet...

Tmuir Distinguished Member

Tmuir

Posted
  • Author
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The spring is not set, it just looked like more than 1/3 rd of the space was occupied by the spring, so I wasn't sure if it was original, or if someone had fitted the wrong size spring in it.

I'll clean it up and reuse it.

On the whole the movement is in far better condition than I was expecting as I know it had some water ingress and was then dropped in methylated spirits to remove the water.:startle:

The anchor and roller jewels are still glued in place and the only rust I can find is limited to mainspring click spring, the dial has some damage which I suspect is due to the meths

jdm Distinguished Member

jdm

Posted
Posted (edited)
20 minutes ago, Tmuir said:

The spring is not set, it just looked like more than 1/3 rd of the space was occupied by the spring, so I wasn't sure if it was original, or if someone had fitted the wrong size spring in it.

Do not take any "rule of thumb" as if carved in stone. Check pic below for a Rolex MS in barrel, pretty much the same I'd say. Maybe the 1/3 proportion was appropriate before metal alloys developed better.05_barrel.jpg

Edited by jdm
Tmuir Distinguished Member

Tmuir

Posted
  • Author
Posted

Thanks jdm, that made an interesting read.

So far I've not worked with any modern watches, this 1970s Seiko being the most modern watch I've touched so I am used to older movements where the mainsprings are shorter. I've learnt something new today now, which makes it a good day.

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Tmuir Distinguished Member

Tmuir

Posted
  • Author
Posted

A measure of the mainspring gives me 0.95 x 0.115 x approx 400 with barrel diameter being 10.5mm so that looks pretty close to me.=

I will try and resuse the original spring, but first I need to make some spacers for my mainspring winder as it is made for much taller springs.

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