Early shock proof device service

[bsoderling]

I recently encountered this type of shock resistant design on a Tissot 27 movement. I suppose this is pre-inca early design ?

 

Any advice available how to remove the cap jewel on the balance side?

 

On the dial side the cap jewel can be taken off and the jewel below is exposed. I suppose it can be cleaned as it is but if there's know how around on the dismounting procedure, I would appreciate it.

 

 

 

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[oldhippy]

 

I know my memory isn’t what it used to be. I think under the balance cock you will find tiny screws that hold it in place. You will need to remove the balance complete in order to get to the screws.

[bsoderling]

Thanks oldhippy, will check.

So it could be the tips of those screws that are visible on the part sticking out from the cap jewel holder?




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[oldhippy]

It could be.

[bsoderling]

And it was... two tiny screws from the other side of the balance cock holds the part in place. I must say that I prefer the Inca design. I can't help wondering why the screws had to go in from the other side of the cock...?

But my problems didn't end there...

When removing the complete balance assembly for cleaning, I noted that a tiny shim was placed under the cock to tilt it slightly, probably to reduce the available height for the balance staff.

When mounting it all again (without the shim), I can't get it to fit. The balance staff is simply to short to fit well into the jewels on both sides. And the pivots look ok.

Measuring the length of the staff with my micrometer I get : 3,310 mm

This is exactly the length I find in the documentation to be the correct for the regular (non-inca/non-shock proof) design whereas the Shock-proof staff is supposed to be 3,360 mm, i.e. 50 um taller. 

My suspicion is that at some point someone replaced the balance with the wrong shorter one and tried to compensate for this by tilting the balance cock a tiny amount. I tried to do this but couln't find a working solution.

I would appreciate any thoughts or comments. Am I looking in the right direction here? Can the 50 um difference explain my problem?

 

[Geo]

Probably a bit late for this, but I couldn't find it earlier.

 

[bsoderling]

Brilliant! Never too late to learn...

I didn't dare to pick apart the cap jewel holder as you did but thought it would clean well enough as it was.

On a side note... when I use the link provided from my tapatalk ipad app, it takes me to a totally different topic. Had to use the link from a regular browser to get to the right one. Strange...

Any thoughts or comments to my extension of this topic regarding the poorly fitting balance staff?





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[Geo]

  On 9/6/2017 at 6:15 PM, bsoderling said:

Any thoughts or comments to my extension of this topic regarding the poorly fitting balance staff?

Expand  

Without having the unit in front of me to study closely, it would be difficult to comment on.

[bsoderling]

No worries...

I guess my best option is to hunt for what I think should be the correct staff for the Shock-resist variety and swap out the one currently in the movement to see if my ideas are correct. I have seen a few out there that should be the one I need.

Another issue I haven't mentioned earlier is that the balance wheel sits so low that it's touching the pallet fork cock in some orientations of the movement, which is another obvious no-no that hopefully strengthens my hypothesis that the balance staff is the wrong one.

I didn't pay more than 10 Euro for the watch, so I should have some hobby budget left to explore this ...

I'll post an update when I have something new to tell.

 

 

[bsoderling]

Hi guys,

Promised some feedback on this one. 

So I got the presumably correct length balance staff and managed to swap that into the balance wheel ok. 

Next problem encountered was that the hairspring collet was loose on the staff and wouldn't stay in place. Either I managed to widen it slightly or the new staff is a tiny bit narrower on that part. 

I found this video by the amazing Bunnspecial, using a hollow stake in the staking tool to reduce the collet ever so slightly and it worked!!  

https://www.youtube.com/watch?v=OBC1utamM6w

 

 

Finally got all the pieces back into the movement again and it seems to run decently. 

Below is a picture of the assembled watch.

The dial isn't much to write home about, but for now I'm happy that it ticks along and I proved my theory correct about the balance staff being the wrong one. Those things need to be pretty spot on to do their job...

 

[matabog]

Congrats!

How long was the new axle?

[bsoderling]

Hi Matabog,

The difference was 50 um and that apparently made a huge difference. I'm just beginning to understand the precision involved in these designs and manufacturing processes...


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[anilv]

Great job troubleshooting!

[matabog]

I would have tried raising the lower balance jewel assembly (that is if it's friction fit), using a jeweling tool to decrease the axial shake.

Would that have worked, I wonder?

Nice job, anyway! How did the balance staff exchange worked?

[bsoderling]

Hello Matabog,

That would for sure have been an interesting thing to try. I suppose it's along the same thinking as when the guy who mounted a too short balance staff tried to shim under the balance cock edge to tilt it slightly downwards. But your idea should be more correct as it doesn't introduce any angle error (and possibly avoids a bunch of other issues as well)

There's a photo of the jewel setting in the thread. Can you tell from that if your idea to shift it would have worked?




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[praezis]

Matabog,

that will not work. Endshake is detrmined by the endstones, not the hole jewels. And they are fixed in position, you cannot shift them with a jewel press...

Frank

[matabog]

@praezisfrom th picture it apears that the entire bottom jewel assemby is caught in a round metal piece which is friction-fit in the mainplate. I would have tried raising that. 

[bsoderling]

My picture is probably misleading as it doesn't show the end stone that is fixed in a small metal plate that fits in the recess visible in the photo.

Had this been an inca-type device with jewel and end stone integrated as one item, I would assume pushing the entire setting in might have worked...?




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[praezis]

Some - only few afaik - Incablocs may be pressed without a stopping edge. But if the staff is wrong, usually the calibrated parts of the staff, that stop the displacement by shock, are wrong, too or missing at all. 

Frank