Teardown + Service: Sea-Gull ST7

The Chinese Mechanical Watch Forum on watchuseek.com has decided and Torsten has supplied it – the next teardown was to be a Sea-Gull ST7. A rare beast indeed, as it never went into production. and there are only a couple of thousand of these watches around. If you want one, you will have to part with the same money that buys you a stainless steel Rolex.

The watch was developed in the late 70s / early 80s, and, with China still a pretty much closed country, this might have been a great product without a market. In China itself, very few could have afforded such a complicated watch with 29 jewels, and outside China, not many would have bought a Chinese watch.

I feel very honoured to have been entrusted with this watch, considering its rarity, so I’m a bit aprehensive!

Crown with Sea-Gull logo, and the crystal is held in place by a bezel

Back with Sea-Gull logo

First look inside

First, I take out the auto winder whilst the movement is still in the case

The finish of the bridges is quite rough, but this is a prototype. Where it matters, the detail is good

As soon as the movement comes out, I take off the hands and the dial and wrap them in watch paper for safety

Love the dial - so 70s!

Odd scratches on the back of the dial. Remind me, what was Mandarin for Tuesday, again?

I take off the day wheel and wrap it straight away

A pretty complex bottom plate assembly - if you pull the crown out to the first stop, you can set the time, and if you pull it out once more, you can set the day by turning in one direction, and the date turning in the other direction

Slowly, I'm working my way through. Have a look at the spring inside a spring right of the 19 - that's going to be fun putting back together

Almost there ...

Bottom plate cleared

Considering I haven't touched the top plate yet (apart from the auto winder), we have quite a few parts already!

I turn the movement around and start off with the barrel and transmission wheel. Lots of gunked up oil under the transmission wheel

Balance cock with balance assembly. I take photos of every component with its screw(s), which makes reassembly so much easier as you can identify the right screw straight away

All bridges removed, pallet fork cock is next. Note that there isn't a centre wheel. First wheel (barrel), then the second wheel next to the barrel (not centred) , which drives the third wheel. Try to figure out the flow of torque through this wheel train. Hint - the middle brass wheel consists of two wheels, co-axial, but turning independently. The cannon pinion in this movement turns freely on an arbor, so don't try to tighten it! Cool stuff!

All wheel pivots are in good shape - that's a relief

Pallet fork with cock

And part one is done - time to do some cleaning. Click on the photo to enlarge it and you will be able to see a huge chunk of dirt right next to the bottom jewel of the balance. There are also very deep grooves left of the balance jewel - I wonder what happened here...

For a thirty year old balance, this looks great - after cleaning

I am amazed how well things brush up - this pinion looks as good as new

I have to admit that I was scratching my head about the power flow through this movement ... On first sight, it looks quite confusing. So after a bit of investigation, here we go: From right to left... The barrel wheel drives the second wheel pinion(not a centre wheel), the second wheel pinion drives the pinion on of the top third wheel. The third wheel consists of wo third wheels, which are one on top of the other. They can in principle turn at different speeds as they are mounted free from each other, but they don't. The second arbor pinion is wide enough to be driven by both wheels, thus locking them together at the same speed. The bottom third wheel drives the fourth wheel pinion, and the fourth wheel drives the escapement wheel pinion. The barrel wheel also drives the lower of the two cannon pinions. These have a friction fit, and the top pinion is used by the time setting mechanism of the bottom plate.


In this photo, you can see how the second arbor pinion locks the two third wheels together at the same speed

This photo shows the cannon pinion. Search for the lower pinion and you can see how it is engaged to the barrel wheel

Very interesting watch – it looks like no money was spared in the construction. Somebody wanted to compete with Swiss watches and not hold back. And I think they did a good job. It does not have the finish of a comparable Swiss movement, but that’s just a bit of polishing. As usual, this movement is more pragmatic and not out to dazzle with polished and ornately brushed bridges and parts – this is made to work well and to last.

The movement is pretty dirty, with a lot of solidified oil and dirt. The good news is that on first sight, no parts are damaged, and I should be able to get this back into tip-top shape.

My guess is that the watch hasn’t been serviced for several decades, if ever. Might well be that the last drop of oil this watch saw was when it was produced.

As my wife is expecting a baby any time now, I might take a couple more days than usual to put the watch back together.

Now to the question if I would prefer this to a Rolex for the same money, here are the reasons for my answer:

  • you can adjust the beat error of the Sea-Gull easily
  • the fourth wheel assembly does not stick out of the wheel bridge as on comparable Rolex movements
  • the barrel is jeweled on the Sea-Gull
  • the Sea-Gull is pretty unique – even though few people will recognise it, you know what you are wearing
  • anyone can buy a Rolex

5:0 for the Sea-Gull, I’m afraid. 😉

March 2nd, 2012

I’ve cleaned all the parts, and it’s time to start on the reassembly. I don’t expect to finish that today (not with my wife going in to labour any minute now 😉 ), but I will start.

All ready to roll. As the barrel bottom jewel isn't accessible from the other side, I've oiled it before putting the barrel in

The wheels go in

Wheel bridge mounted and pallet fork and cock in

When inspecting the pallet cock and oiling the pallets, I notice something that you don’t really want to see….

You can see how the left (top) pallet is wonky and lose. This normally happens if you put the pallet fork into the cleaning fluid that dissolves the shellac. But honestly, I didn't. Not that I haven't done that before, but I left the pallet fork with the dial and hands.

I put the pallet fork on a straight surface with a hole where the pivot is so that it's lying flat. Now I can straighten out the pallet and glue it back in with a tiny drop of shellac

Shellac applied - this forces a 24 hour wait as I'm not even going to look sideways at the pallet fork before the 24 hours are up

Monday, March 5th, 2012

The old shellac on the pallet fork had turned into goo – not hard at all, but more the consistency of rubber. So time to clean everything, take both pallet jewels out, and re-set them.

The pallet stones need adjusting. As you can see in this photo, even though the pallet fork is all the way down, the lower pallet jewel does not go far enough into the escapement wheel to lock the escapement. It needs to be pulled out further from the pallet fork

In the upper position, the upper pallet goes too far into the escapement wheel and needs to be pushed in. I could of course adjust the pallet fork lever position, but I don't want to start bending pallet forks before I haven't tried to adjust the jewels

Here we go - you can see the left pallet jewel pushed in all the way, and the right pallet jewel pulled out a bit. All is then glued into place with new shellac, with the old shellac carefully removed from the pallet fork and the jewels. Another 24 hour wait for the shellac to dry completely

Whilst waiting for the shellac to dry, I put the wheel bridge back in

Tuesday, March 6th, 2012

My wife’s contractions have set in – I won’t finish this watch before the baby is born 😉

The pallet fork is ready to go in

I mount the balance and the watch starts immediately

Time to turn my attention to the bottom plate

If you like fiddly, put those two springs back in

I put the winding shaft in and test all the setting stuff - and notice that the minute wheel slips. First, the pallet jewels, now that. Not my lucky watch, this

This is the culprit. The inner wheel slips within the outer wheel, so when the minute hand moves, the hour hand stays

Time to get my trusted staking set out

The staking slightly diminishes the inner diameter of the wheel, so I take a small drill to enlarge it again

Disaster strikes! The inner wheel breaks whilst drilling. I am absolutely gutted

Now I have to find a replacement minute wheel. This is terrible – spare parts for an ST7 are hen’s teeth. With a bit of luck, the minute wheel of another watch fits. With a lot of luck…

What I need is: outer diameter 5.5mm, 30 teeth, inner wheel diameter 1.9 mm, 8 teeth.

Never fear, all comes to a good conclusion 6 weeks later.

6 thoughts on “Teardown + Service: Sea-Gull ST7

  1. Kudos to you for resetting the pallet stones! Phew – I’d have been filled with despair at the discovery of loose stones there. How you can manipulate such tiny items is beyond me. I have done a couple of strip downs of basic three hand pin pallet movements and got them apart and back together working well, but it’ll be a long time before I could even do that with confidence. This ST7 looks like a nightmare of complexity.

    Hope all is going well on the domestic front.

  2. Mate
    Again a fabulous journey into Chinese Watches. I wait for each article.

    This was special for me as I have one….


  3. Love these tear downs Christian.

    Is the bottom pallet jewel damaged? The hole seems elongated in the photo where you referenced a chunk of dirt by the balance lower jewel. It may be a photo artefact but the hole looks worn to me.


    • I checked and the jewels are all fine. I have fallen for this on another occasion. The angle at which the photo is taken distorts the image of the jewel.



  4. Pingback: Teardown Sea-Gull ST7

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