Has anyone heard of such a '9F81' movement? We know of the 9F82, 83, 85 and 86 gmt. Also the thicker 9F61 and 9F62.

Prolific dealer VintageSeikoNL asserts on a webpage that caliber 9581A was re-designed the 9F81, and as far as I can tell hasn't been challenged:

The 9587/1 then is a great watch with nostalgic design, even if slightly small for today’s taste. Its movement is a Seiko Quartz Cal 958xA, with 7 Jewels, 32.768 Hz, thermal compensation, anti-magnetic, accuracy: +/- 10 sec/year, 3-year battery life. It is one of the very few Seiko watches that uses a 17mm lug width. This GS is one of the world’s most accurate watches even today, 20 years later. It is also one of the cheapest ways to get a GS.

The outcome of this endeavor was a quartz module that was larger and more robust than previous “thin” Seiko high end quartzes, housed in practical but iconic (Tanaka) case design and with dials that have been uniquely Grand Seiko ever since.

The 9581A, later re-designated 9F81, is equipped with a unique Twin Pulse Control high-torque stepper motor which makes each second hand movement in two fluid pulses to reduce energy consumption. Instantaneous date change occurs over just 0.5 milliseconds, while a backlash auto-adjustment mechanism eliminates stepper error. Furthermore, the movement module is air-tight...

The SBGS line had the 9581 and 9582, that is not disputed. But that 9581 is a.k.a. 9F81?

The 9581 has the battery clockwise from the stem (dial side basis):
View attachment 17841912

Whereas on the 9F82 the battery is counterclockwise from stem:
View attachment 17841914

Aside from the mirror imaging, there is a superficial similarity about the plates.

The few Google hits for '9F81' are either reposts of the above, or typos that actually mean 9F61.

The 95 and 9F are definitively not the same movements.

The 95 does not have an anti-backlash spring or instantaneous date change. The 9581 does not even have a date, so why is it mentioned? The bit about the module being airtight is also repeated here, which is is not the case for any of the movements.

Sure the 9F is an evolution of the 95 and they have similarities, but they are different movements. I have serviced both, and the quality of the 9F is so much better in my opinion.

 

Thanks for confirming with your personal knowledge, what I had suspected.

The 9581 does not even have a date, so why is it mentioned?

To be fair, going by Seiko numbering conventions any such '9F81' like the 9F61, would also not have a date.

Again, thanks.

Prolific dealer VintageSeikoNL asserts on a webpage that caliber 9581A was re-designed the 9F81

Sorry, I meant re-designated, not 're-designed'.

 

From what I’ve heard, the 9f8X was made with the intent of making the date positioned further away from the center, better suited for bigger dials and cases.

Do you mean positioned further away from them the center, compared to the 958x?

Or are you saying 9F82 has a larger diameter date wheel than the 9F62? I can't find much information on the difference between the 9F82 and 9F62 aside from this TZUK anecdote that the 9F6x are merely thicker.

The verso of these movements look the same size (center = 9F62, flanked by 9F86 and 9F85):
View attachment 17842342

I went to the trouble of pixel peeping the 9F83 vs 9F85 to check if the sizes were the same. Conclusion, to confidence level >99.5%, yes:
View attachment 17842346
View attachment 17842345

9F83: 332 px movement / 140 px battery = 2.37 ratio
9F85: 372 px movement / 156 px battery = 2.38 ratio

The 9F83 and 9F85 should be the same size, given by the number 8. The 9F62 is a smaller movement.

This allows for two different date positions based on the size of the watch, as Barbababa said.

 

The 9F83 and 9F85 should be the same size, given by the number 8. The 9F62 is a smaller movement.

This allows for two different date positions based on the size of the watch, as Barbababa said.

I can accept that 9F62 has a smaller diameter date disc.

And I acknowledge that no less than Seiko says 9F62 is smaller

However, if you look at the photos of 9F62 and 9F85 and measure the caliber body proper relative to the battery, you will find the perhaps trivial fact that the bodies proper are the same size, and that 9F85 is only larger due its flange

 

The 9F83 and 9F85 should be the same size, given by the number 8. The 9F62 is a smaller movement.

This allows for two different date positions based on the size of the watch, as Barbababa said.

I can accept that 9F62 has a smaller diameter date disc.

And I acknowledge that no less than Seiko says 9F63 is smaller

However, if you look at the photos of 9F62 and 9F85 and measure the caliber body proper relative to the battery, you will find that they are the same size, and that 9F82 is only larger due its flange
(Will edit to add photo)

That is true.
I am pretty sure they are basically the same movement except a bigger mainplate (flange) and some components of the date mechanism.

 

Thanks @Barbababa and @Bauta

A 9F stat that I would really like to learn are the respective thicknesses of 9F61, 9F82, 9F85 and 9F86.

 

Hi, Mandaue--Long ago, I saw a note on Seiya's Japanese site saying that the dimensions of the 9F6x were 27 x 26 x 3.1 mm; the 9F8x = 29 x 26 x 3.1. I cannot vouch for the accuracy of either the measurements, or of my record of them, and the Seiya site seems to be "down."

At the time the 9587 GS was reintroduced, Seiko's design was still influenced by the 1980's "thin watch" esthetic, and the 9587 movement and watch case are much thinner than the 9F and corresponding cases, and lack the train backlash prevention that the 9F provides. Given that the original series of Seiko's 1970's hi-end quartz models had a "second-jumper" that prevented backlash, and that these cases never got thinner than 9mm, I'm guessing there is a sort of technical limit to how thin the movement can be made and still provide anti-backlash second-hand minute-track alignment.

I'm sure the 9F's are independent designs, not in the 95xx series.

ReggieH