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Discussion Starter · #1 · (Edited)
As voted for by you, here is the teardown of the Sea-Gull ST-7 Torsten supplied so kindly. It's a great watch and I feel honoured having the opportunity to service it. And it does need a service!

All is well, though, and on first inspection, there doesn't seem to be any excessive wear.

Great watch!

Teardown + Service: Sea-Gull ST7 | Watch Guy

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Enjoy,

Christian

P.S.: The reassembly might take a couple of days longer as my wife is expecting to give birth any day now!

P.P.S.: Chascomm - could you do me a favour and put a link on the Sea-Gull page of the Chinese Watch Wiki (if that's ok)
 

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Thanks for taking good care of the ST7. Another excellent tear down. All the best for the coming days from Hong Kong.
 

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Wow! That's going to take a while to absorb all the details. That calendar mechanism looks frighteningly complex.

We'll make sure there is a ink on the Resources page along with the other teardowns (or should that be 'tears-down'? :think: What is the correct plural for 'teardown'?)


And best wishes to you and your wife!
 

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Portugieser chrono on 16mm Forstner Komfit
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Really nice teardown. I like the big pics! And best of wishes to you and your wife!

If I may make one suggestion: At first glance I thought the big pics could use a tiny bit of sharpening; but maybe it's just depth of field. In that case using a tripod or upping the ISO (or lighting) in order to be able to stop down (getting away from f/2.8) might do the job. I don't know whether an Ixus 85 has manual settings; but it might stop down on its own if you give it more light or select a higher ISO.
 

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Another spectacular account of a watch dismantling.

Is the lower pallet jewel worn? On the photo where you referenced a chunk of dirt near the lower balance jewel, the lower pallet jewel looks to have a distorted hole in it. It looks like wear to me, but the effect may be an artefact of the photo for all I know.

If the watch may not have been serviced in thirty years, has it been used all the time? Probably hard to know as the present owner is unlikely to have had it all the time. I'd really like to know how long a well made watch will stand neglect and not be destroyed. To know that, you'd need to know it had been run 24/7 all the time.
 

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Discussion Starter · #8 ·
Another spectacular account of a watch dismantling.

Is the lower pallet jewel worn? On the photo where you referenced a chunk of dirt near the lower balance jewel, the lower pallet jewel looks to have a distorted hole in it. It looks like wear to me, but the effect may be an artefact of the photo for all I know.

If the watch may not have been serviced in thirty years, has it been used all the time? Probably hard to know as the present owner is unlikely to have had it all the time. I'd really like to know how long a well made watch will stand neglect and not be destroyed. To know that, you'd need to know it had been run 24/7 all the time.
I've fallen for that in the past as well - it's the distortion from the angle at which the photo is taken.

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I hope this one shows better that the jewels are actually fine.
Hard to tell how much the watch was actually used ... From the scratches and the state of the screws, I would say the watch has been taken apart at least once after manufacture. But the last service must have been well over a decade ago, judging from the state of the oil residue - or it was used under harsh conditions (temperature, dust, sweat, humidity).

Christian
 

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The present owner can only account for the last three years during which the watch has lived a quiet life tugged away in a sealed plastic bag in a box.:):)
 

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Discussion Starter · #10 · (Edited)
Now I think I've figured out how the power flows through the wheel train.
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Starting from the right, the barrel drives the pinion of the second wheel (not in the centre, so I won't call it centre wheel), the second wheel drives the pinion of the third wheel (which is a double wheel, with both wheels in principle being capable of turning on their own as they are co-axial), the lower of those wheels then drives the fourth wheel, which drives the escapement wheel.

So far, so good.

What is odd though is that the double third wheel(s) drives the pinion of the second arbor:
Reflection Plant
If you look carefully, you can see that the pinion of the second arbor is in contact with both third wheels. So even though they can in principle turn independently, they are power-coupled by the pinion and have to turn at the same speed. So the only explanation I can find for the double third wheel is that is can transmit twice the power and is less prone to wear. Any other ideas?

Also, the barrel wheel drives the cannon pinion directly! As you can see, the cannon pinon has two pinions. The lower one is driven by the barrel wheel, and the upper one is turned by the setting mechanism on the bottom plate. So the cannon pinion has a lose fit on the bottom plate, but the friction fit is between the two pinions of the cannon pinion.

Pink Light Water
In this photo, you have to look carefully. The view is from the bottom plate, with the cannon pinion visible. Search for the lower pinion of the cannon pinion, and you can see how it is engaged with the barrel wheel.
 

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It just gets more interesting!

The double 3rd wheel is not unusual in a movement with indirectly-driven second hand, but I'd never seen the two wheels so close. So I couldn't figure out how it worked until you showed us the close-up. It really does look like a temporary fix that would have been addressed more efficiently with a single wheel in a full production version had that eventuated.

As for the cannon pinion; the same solution was used by Timex in their main line of pin-lever movements made from about 1957 to 1980. Like the ST7, the 2nd wheel is offset (eliminating the need for the intermediate plate of a coaxial train e.g. Tongji) and the cannon-pinion sits on the dial side driven straight off the barrel.

Here is the Timex pinion:



And here is the front side of the main plate with the pinion removed:



The setting mechanism is a crude rocking-bar arrangement, but the pinion functions the same way.

So Christian, your next challenge ;-) is to explain to us how the auto-winding functions.
 

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This is exquisite work. Thank you for sharing your process with us. I'm still pretty naive when it comes to watch movement details, and I learn more every time I read your work. I wish you great joy with the new baby!
 

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Discussion Starter · #13 ·
It just gets more interesting!

The double 3rd wheel is not unusual in a movement with indirectly-driven second hand, but I'd never seen the two wheels so close. So I couldn't figure out how it worked until you showed us the close-up. It really does look like a temporary fix that would have been addressed more efficiently with a single wheel in a full production version had that eventuated.

As for the cannon pinion; the same solution was used by Timex in their main line of pin-lever movements made from about 1957 to 1980. Like the ST7, the 2nd wheel is offset (eliminating the need for the intermediate plate of a coaxial train e.g. Tongji) and the cannon-pinion sits on the dial side driven straight off the barrel.

Here is the Timex pinion:

And here is the front side of the main plate with the pinion removed:

The setting mechanism is a crude rocking-bar arrangement, but the pinion functions the same way.

So Christian, your next challenge ;-) is to explain to us how the auto-winding functions.
I'm with you there - that double third wheel looks like a pre-production arrangement.

Never fiddled with those Timexes - interesting to see the photos! As you said, it saves you the probably quite expensive co-axial arrangement with an intermediate bridge you would otherwise need if you want a central second. From a purely technical point, I must say that I find the not-centred second wheel the cleaner solution.

What surprised me is that the central arbor for the second hand is not jewelled - with the normal Chinese love for jewels, I would have expected at least one on the top plate side! Not that it probably matters much in terms of wear or friction.

Now for the challenge of the auto-winder - look! That's me running for the hills! But I will try. Looks fiendishly complicated on first sight, though.
 

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Nice save! That's the first time I've seen the widening-the-wheel-with-hole-punch trick.

And thanks for explaining the auto-winding. It seems to be something like the Felsa 'Bidynator' design with the pair of little wheels on the oscillating mounting. I've got something similar in a Poljot 2416, except that the wheels pivot on the underside of the rotor rather than on the movement as in the ST7. I've heard watchmakers praise this system for its superior reliability compared to the ETA bidirectional system (as in the automatic Tongji) but the technical downside is the clearance needed to swing from one little wheel to the other leads to a larger 'dead angle' of rotor movement when changing direction.

The extra jewel suggests to me that the engineers had not fully committed to this winding mechanism and more development may have ensued had the project continued.
 

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Discussion Starter · #16 ·
Nice save! That's the first time I've seen the widening-the-wheel-with-hole-punch trick.

And thanks for explaining the auto-winding. It seems to be something like the Felsa 'Bidynator' design with the pair of little wheels on the oscillating mounting. I've got something similar in a Poljot 2416, except that the wheels pivot on the underside of the rotor rather than on the movement as in the ST7. I've heard watchmakers praise this system for its superior reliability compared to the ETA bidirectional system (as in the automatic Tongji) but the technical downside is the clearance needed to swing from one little wheel to the other leads to a larger 'dead angle' of rotor movement when changing direction.

The extra jewel suggests to me that the engineers had not fully committed to this winding mechanism and more development may have ensued had the project continued.
Yes, I'm with you there. The "spare" jewel probably comes from a different winder design. I have another ST7 (manual wind) on my bench (also from Torsten), which has a different day/date change mechanism and other small differences, so I presume there was quite a bit of changing during the development process going on. And lots of room for changes as well, if I look at that double-wheel construction etc. Very much a work in progress. Not something you would find in a Patek Philippe ;-)
 

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Really enjoyed reading this story, and glad it had a happy ending. I feel like my retirement hobby someday may be watchmaking (or fiddling most likely), if my eyesight holds up haha.
 

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Very much a work in progress. Not something you would find in a Patek Philippe ;-)
Or at least not any Patek Philippe that would ever fall into the hands of the general public.
 

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Discussion Starter · #19 ·
Or at least not any Patek Philippe that would ever fall into the hands of the general public.
Do you actually know how all these ST7s made it out of the factory? Did they plan to sell them as they went along developing the watch?

Cheers,

Christian
 

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Do you actually know how all these ST7s made it out of the factory? Did they plan to sell them as they went along developing the watch?
That's really a question for one of the experts like Joel Chan. My understanding is that a test batch were assembled (day/date, automatic) and then sold in the usual test batch way to factory employees. There were significant stocks of parts left over that were subsequently assembled (date only, hand-winding) and sold. The interval between these two 'releases' was a matter of years I think.

Note the difference in specification between the first batch and the second 'left-overs' batch. The parts missing match those parts that your investigations suggest were not finalised designs i.e. auto-winding and calendar.
 
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