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How to tell the difference between Seiko 7S26A, B, C

Tmuir

By Tmuir
in Watch Repairs Help & Advice

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Tmuir Distinguished Member

Tmuir

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I've got a Seiko 5 watch that I recently restored the case is 7019-8180, but the original movement has been swapped out for what I think is a Seiko 7S26 movement.

The oscillating weight needs replacing on this movement, but as it does not have its calibre number on it I cant work out if its a 7S26A, B or 7S26C and I believe they all use different oscillating weights.

If anyone can tell me what to look for to ID the movement that would be great.

A couple of pictures of the movement below,  if you need any photos of other parts let me know.

I take no responsibility for the marks on the movement, its how I found it, but after servicing it is running with 0.0 beat error and an amplitude around 280 degrees and acuracy of around +15 - 20 seconds a day between dial up and dial down

seiko1.jpg

seiko2.jpg

Tmuir Distinguished Member

Tmuir

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I think I have managed to answer my own question, but would like confirmation.

My movement oscillating weight is a quarter rather than half circle which I think makes it an 'A'.

Can someone confirm that?

seiko3.jpg

jdm Distinguished Member

jdm

Posted
Posted

As mentioned already in similar topics, the weights are all interchangeable, no matter their shape or marking, and so are most other parts. The most notable evolution is Etachron introduced in B version, and calendar plate with 4 same flat screws in C version.


For a detailed list of parts interchangeability, check the table that I maintain at https://docs.google.com/spreadsheets/d/e/2PACX-1vRN2UULQKTfKmhRStZhDdIOIQrqd6sPB-g6x2SKyQQjOvTBjG_7TQXQhAT4f1WqAX5QAPkIimi-3jqd/pubhtml

Tmuir Distinguished Member

Tmuir

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Thanks for that.

I've downloaded your document and added the oscillating weight to my Cousins order which I will be placing later tonight.

mikepilk Distinguished Member

mikepilk

Posted
Posted
3 minutes ago, Tmuir said:

Thanks for that.

I've downloaded your document and added the oscillating weight to my Cousins order which I will be placing later tonight.

I've found Speedtimerkollektion useful for cheap Seiko parts

jdm Distinguished Member

jdm

Posted
Posted
6 minutes ago, Tmuir said:

I've downloaded your document and added the oscillating weight to my Cousins order which I will be placing later tonight.

Just PM with your address, I have many to spare.

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