Tissot Seastar Cal 794 mainspring issues

[Simeon]

I bought a lovely 1972 Tissot Seastar automatic with the Cal. 794 movement and wore it for a few days.

It kept good time but on one occasion it stopped and needed a wind to get it started. When I first put it on, I didn't wind it, just started it with a flick of the wrist and left it to wind itself. Unsure about how effective the automatic works might be, I decided to give it a a full wind to let it get a head start and not rely on the automatic wind as I may be too passive to keep it wound.

Winding the watch felt 'interesting' with some slipping but it took the wind and worked fine for a few more days. 

Yesterday afternoon I checked the time to find it had stopped. Winding the watch feels very strange now and it doesn't start.  I took the back off and watched the motion of the barrel when winding, it turns OK with the crown wheel  but when I go to let the wind down, there is no stored energy. 

Broken mainspring/ bridle?

I am a bit nervous about servicing this watch as the 794 seems to be unnecessarily complicated and difficult to assemble correctly.  Would it be wrong to basically dissassemble the watch only far enough to change the barrel/ mainspring. Install a new GR mainspring, reassemble and call it a day? Kick the can down the road until I have honed my skills more?

 

[Waggy]

The mainspring would be my prime suspect, once you get to it, installing a new mainspring is fairly simple. But in getting to the spring barrel you are about 50-75% of the way through a complete disassemble, so you may as well go the 'whole hog'. I don't know your experience level, but if you are just starting your journey I would get some more experience under your belt before risking a service on this watch, a good excuse/motivation to get started in the hobby. Other than that you could maybe find a watch maker in your location and get them to do the change out if you aren't ready to take it on yourself yet.

Just looking at the watch it looks like it is about due a service, difficult to be sure from a picture, but maybe worth biting the bullet and get it serviced, or bide your time and do it yourself when you are feeling confident

 

[Simeon]

I have successfully serviced 10 movements, and started another 3 (waiting on parts). Only worked on one automatic (a Seiko) that I haven't finished yet. Mainly simple manual wind Soviet movements, some with day / date. 

I think that Tissot would be a bit beyond me. 

I can't really do anything more complex than strip things down, clean and replace parts. If I don't have a detailed run through (video /, forum thread, blog entry etc), I take lots of photos. I have got to the point where I typically don't lose or break anything but I struggle a bit with more intricate stuff (Diafix!)

[Jon]

2 hours ago, Simeon said:

I think that Tissot would be a bit beyond me. 

The auto mechanism is pretty easy to work out on this movement. Once that is removed with the rotor, then it is nothing that you can't handle.

Here's a similar movement with some pics.

This is with the rotor removed, by pulling back the retaining clip/spring

This is the auto mechanism

This is the automatic click

There is a strange part that keeps one of the wheels in place that is held down by a screw as you can see in this photo. Turn the screw anticlockwise to allow the wheel to be removed as the slim piece of metal with a cut-out disengages from it and when assembling turn the screw clockwise so that slim metal retaining piece engages with the side of the wheel.

 

[Knebo]

3 hours ago, Simeon said:

I think that Tissot would be a bit beyond me. 

33 minutes ago, Jon said:

The auto mechanism is pretty easy to work out on this movement. Once that is removed with the rotor, then it is nothing that you can't handle

I agree with @Jon, the Tissot 79x are pretty straight forward and well-designed movements. If you can handle Seikos, you can handle this one, too. Unless you have never done any calendar works. 

 

4 hours ago, Simeon said:

Would it be wrong to basically dissassemble the watch only far enough to change the barrel/ mainspring. Install a new GR mainspring, reassemble and call it a day

If you want to go down this route, you are lucky in the sense that the mainspring barrel is easily accessible WITHOUT removing the train wheels/bridge (you could maybe even leave the balance on, but then take extra care).

See below.

When you get to that point, make sure you gently "shake out" the barrel instead of roughly yanking it out and potentially bending the center wheel.

 

You might also find this thread useful (783 is the 784 without calendar):

 

Edited June 6, 2024 by Knebo

[JohnR725]

9 hours ago, Simeon said:

Broken mainspring/ bridle?

I am a bit nervous about servicing this watch as the 794 seems to be unnecessarily complicated and difficult to assemble correctly.  Would it be wrong to basically dissassemble the watch only far enough to change the barrel/ mainspring. Install a new GR mainspring, reassemble and call it a day? Kick the can down the road until I have honed my skills more?

You wouldn't happen to know the service history of this watch would you? Or would you have A timing machine like how well is the watch running when it is running? From time to time watches need to be serviced it's not enough to just change the mainspring and you're good to go.

8 hours ago, Simeon said:

Only worked on one automatic (a Seiko) that I haven't finished yet. Mainly simple manual wind Soviet movements, some with day / date. 

I think that Tissot would be a bit beyond me. 

I've been reading the replies your getting apparently working on one Seiko automatic that you haven't finished yet makes you an automatic expert so you have nothing to fear. Especially because the people who posted all the comments about no need to fear anything will help you straight out whatever happens just in case it should happen. But don't worry based on the replies watch repair is super easy no skills required.

To be honest normally I don't care what people work on if you want to start with a Rolex I would encourage it I'd typically no longer will make any suggestions at all of people skill level. But if you don't feel comfortable Your the one doing the work they are not they have experience and they forgot what it's like to be in your position. If it makes you feel better finish the Seiko first or anything else you need to do to make you feel better about moving onto the next watch.

9 hours ago, Waggy said:

once you get to it, installing a new mainspring is fairly simple

Oh and minor reminder here this is an automatic watch and you will require breaking grease if you want your automatic mainspring to work correctly

 

 

 

[Simeon]

Thanks for all the replies.

I think I will keep the watch untouched until I feel more confident to complete a full service. I had hoped to get a bit more use out of the watch before having to service plus it pains me to leave something 'broken' in the drawer and not get in and fix it.

While I have no idea of its service history (no service marks inside the case back) it was running pretty well (tested with a phone app only) and certainly performing OK 'on the wrist' hence consideration of the mainspring fix.  I have to wonder why the spring might have failed (previous bodging by another owner kinking the spring? over winding because the bridle is not slipping for some reason?) so that may be a sign that service was required regardless of its performance.

What are the possible causes of a mainspring break? Anything that might suggest about the condition of the rest of the movement?

 

[Knebo]

12 hours ago, JohnR725 said:

21 hours ago, Simeon said:

Only worked on one automatic (a Seiko) that I haven't finished yet. Mainly simple manual wind Soviet movements, some with day / date. 

I think that Tissot would be a bit beyond me. 

I've been reading the replies your getting apparently working on one Seiko automatic that you haven't finished yet makes you an automatic expert so you have nothing to fear. Especially because the people who posted all the comments about no need to fear anything will help you straight out whatever happens just in case it should happen. But don't worry based on the replies watch repair is super easy no skills required.

To be honest normally I don't care what people work on if you want to start with a Rolex I would encourage it I'd typically no longer will make any suggestions at all of people skill level. But if you don't feel comfortable Your the one doing the work they are not they have experience and they forgot what it's like to be in your position. If it makes you feel better finish the Seiko first or anything else you need to do to make you feel better about moving onto the next watch.

Ok, I'll admit that @JohnR725 has a point here.

First and foremost, YOU decide. And YOU have to be comfortable doing it.

It's also good advice to finish the automatic Seiko before going to the next watch.

 

12 hours ago, JohnR725 said:

they have experience and they forgot what it's like to be in your position

In defense of the "encouragement" posted above: when I serviced the Tissot 783, it was actually my second automatic watch and it was only about one year ago. So I didn't forget how it feels being in your position. 

Without a doubt, there is a learning curve. But I, personally (!!!), found it quite doable. It was a simpler auto system than some ETAs, Omegas and Rolexes that I worked on afterwards. 

But very important: this is only gentle encouragement. Nobody here is "pushing you" to try.

 

And that said, I fully support your decision to...

5 hours ago, Simeon said:

keep the watch untouched until I feel more confident to complete a full service

 

 

 

[JohnR725]

10 hours ago, Knebo said:

In defense of the "encouragement" posted above: when I serviced the Tissot 783, it was actually my second automatic watch and it was only about one year ago. So I didn't forget how it feels being in your position. 

Without a doubt, there is a learning curve. But I, personally (!!!), found it quite doable. It was a simpler auto system than some ETAs, Omegas and Rolexes that I worked on afterwards. 

We end up with an interesting problem here and  you've made a very good point super easy to do much easier than other watches okay sounds outstanding. But this is based on your experience how does my experience differ?

Seattle is a very interesting location for learning watch repair. There is a community college that was teaching a class and I was the say 30 years but I think it's much longer than that and that class has evolved so currently its under Rolex sponsorship. The used to have a Thursday evening class open to anybody but Rolex doesn't like anybody so the Thursday evening class ultimately became a school teaching hobbyists. For quite a number years I was teaching a hobbyist watch repair. This gives me greater exposure to people and seeing their various skill sets. So while you found this watch super easy my experience says that not everyone would agree with you.

One of my greatest amusements of quite a few would be in order to go to college to get the Rolex program you have to pass an entrance exam. Then traced the exam basically requires you to have watch repair skills which I find quite amusing if you're going to school to learn watch repair now you have to learn watch repair before you go to the school pass the test. We had a student who failed this test and yes there are some people that watch repair really isn't there a thing. So yes the skill sets of individuals can vary by quite a bit and just because URI might find this easy doesn't mean somebody else Will or who knows they might find it even easier.

On 6/6/2024 at 3:41 AM, Simeon said:

Tissot Seastar automatic with the Cal. 794 movement

One of the questions that often comes up for people relatively new to watch repair is technical information. Mike service guides lubrication guides detailed instructions. Especially somebody who came from servicing and automobile were the often be aftermarket books lots and lots of books and in watch repair which is great technical do we have technical manuals well sort of?

Often times with any of the older documentation it was probably scanned by material houses for the sole purpose of hearts. So even if a technical guide with service information existed all they got scanned was the parts.

I've attached some documentation the parts stuff came from cousins notice zero servicing. The indication for the 794 is it's very similar to the 784 – 2. As I scanned those to a PDF a while back for somebody I've added in the 794 for you and combined with the other stuff you have up above it should make things a little bit easier.

 

3805_Tissot 794_Smaller cousins.pdf 2789_Tissot 781,782,783,784.pdf Tissot Service Technique No 23 781 782 783 784.PDF Tissot Service Technique No 30 Modifications on Calibers 782 783 784.PDF Tissot Service Technique No 35 Calibers 781-1 782-1 783-1 784-1.PDF Tissot Service Technique No 43 caliber Tissot 794 Visoday.PDF

[nevenbekriev]

On 6/6/2024 at 1:41 PM, Simeon said:

Yesterday afternoon I checked the time to find it had stopped. Winding the watch feels very strange now and it doesn't start.  I took the back off and watched the motion of the barrel when winding, it turns OK with the crown wheel  but when I go to let the wind down, there is no stored energy. 

Broken mainspring/ bridle?

 

Regardless all the conversation till here, I will ask HOW exactly did You try to let the wind of the spring down? I meam I doubt that You are not aware that this is not possible by just detouching the click in automatic watches...

[JohnR725]

16 hours ago, Simeon said:

While I have no idea of its service history (no service marks inside the case back) it was running pretty well (tested with a phone app only) and certainly performing OK 'on the wrist' hence consideration of the mainspring fix.  I have to wonder why the spring might have failed (previous bodging by another owner kinking the spring? over winding because the bridle is not slipping for some reason?) so that may be a sign that service was required regardless of its performance.

What are the possible causes of a mainspring break? Anything that might suggest about the condition of the rest of the movement?

On 6/6/2024 at 3:41 AM, Simeon said:

I bought a lovely 1972 Tissot Seastar automatic with the Cal. 794 movement and wore it for a few days.

I had to go back to the beginning which is why quoted something so you purchased a 1972 watch. In other words a 52-year-old watch.

Then testing with the phone app as far as I'm concerned typically is a waste of time. Typically phone apps use the microphone of the phone which is not designed for picking up properly the sounds of the watch and often times we've had well basically phone apps are a waste of time. You really need to get something better for diagnosing and looking at watch problems.

So basically we have a 52-year-old watch that conceivably has never been serviced that is now having issues.

17 hours ago, Simeon said:

What are the possible causes of a mainspring break? Anything that might suggest about the condition of the rest of the movement?

The condition of the rest the watch would be visual observation typically when disassembling for a complete service or if the watches it all running a decent timing machine of some sort versus a worthless phone  app. Until you disassemble the mainspring you don't actually know if it's broken or not and if the watches never been serviced yes mainsprings break. Even unbreakable mainsprings break. But the problem with the mainspring is it's in the mainspring barrel and we don't have x-ray vision so the mainspring barrel has to be disassembled.

On 6/6/2024 at 4:26 AM, Simeon said:

Only worked on one automatic (a Seiko) that I haven't finished yet.

Oh and Seiko's it looks easier than this watch doesn't it? But is it easier? Sometimes looks can be deceiving whereas as others have pointed out this is just a decent mechanical watch with an automatic that action looks quite simple versus the Seiko that looks simple that typically has a lot of wheels under a full plate.

Also unlike a Seiko you can remove the automatic and this becomes a manual watch. So as others of said it's not really a super complicated watch it just looks complicated but. You really need to practice disassembling and reassembling even just one watch even possibly for an entire week or two. Ever wonder how the students in school at least serious professional schools get so good by practicing on the same watch over and over and over again. Need to practice and to have a real good feel for what you're doing and then a complete service of this watch I think as opposed to a Band-Aid fix of a new mainspring as we do not really know the condition of the watch at all or anything else is going on.