AS 1920 vs GP cal. 440 balance complete

[Xilikon]

I have a Girard Perregaux 9377GA I'm restoring and it house a GP caliber 440 movement which is based on AS 1920. Obviously, there is no parts available if i search with GP 440 but with AS 1920, there is a lot so I ordered a balance complete for AS 1920 at Cousins. I received it now but upon checking, I noticed that the GP 440 have the hairspring without a stem, just a long terminal curve and the balance cock have the "plates" to pinch the hairspring while the new balance have a stud attached to the terminal curve and the curve is much much shorter. The "stem" on the balance cock is not removable (I tried pushing but the whole regulator assembly flew off, causing a small heart attack but after 30 mins of fiddling, i managed to reassemble the regulator assembly).

I'm wondering if it is ok if I can pull the old hairspring from the old balance and install on the new balance so the hairspring work with that setup ? Beside the hairspring, the balance looks identical.

Having the terminal curve without a stud attached mean it is more adjustable ? The GP 440 is an observatory chronometer (precursor to COSC) so I guess the adjustability range is greater than a standard movement.

Here is a photo to illustrate the difference :

Edited April 29, 2021 by Xilikon

[Nucejoe]

Hairspring off of one might not produce the right beat with the other wheel.

You also degrade the perfect poise each balance complete already has.

Both calibers originally came with chrono grade oscilators whereas I am not sure if the aftermarket one you got from cousins is chrono grade as well. 

So anyway you look at it,  you risk loosing the precision your watch suppose to deliver by transferring hairspring.

Above picture shows a removable stud, transferring a stud to other will not affect your oscilators grade. 

 

[Nucejoe]

1 minute ago, Nucejoe said:

Hairspring off of one might not produce the right beat with the other wheel.

You also degrade the perfect poise each balance complete already has.

Both calibers originally came with chrono grade oscilators whereas I am not sure if the aftermarket one you got from cousins is chrono grade as well. 

So anyway you look at it,  you risk loosing the precision your watch suppose to deliver by transferring hairspring.

Above picture shows a removable stud, transferring a stud to other will not affect your oscilators grade. 

 

neither cutting hairspring affets the grade,  to get rid of the stud. Cut as close to the stud as you can, use a nail clipper.

[Xilikon]

1 hour ago, Nucejoe said:

Hairspring off of one might not produce the right beat with the other wheel.

You also degrade the perfect poise each balance complete already has.

Both calibers originally came with chrono grade oscilators whereas I am not sure if the aftermarket one you got from cousins is chrono grade as well. 

So anyway you look at it,  you risk loosing the precision your watch suppose to deliver by transferring hairspring.

Above picture shows a removable stud, transferring a stud to other will not affect your oscilators grade. 

 

It's not an aftermarket, it's the original A Schild package, hence the surprise.

About poising, I thought it was done without the hairspring so the balance itself is supposed to be well poised ?

 

1 hour ago, Nucejoe said:

neither cutting hairspring affets the grade,  to get rid of the stud. Cut as close to the stud as you can, use a nail clipper.

The original hairspring was attached close to the end of the attachment point on the balance cock.

 

If we look at the original someone else did, it's the same way with the hairspring getting a bit further than the stud :

https://watchguy.co.uk/cgi-bin/media?image=IMG_3313.JPG&email=&wat_id=2270

[Xilikon]

To be clear, the left is the old one and correct while the right is the new one with the terminal curve already too short.

The other way is to buy a balance staff but i don't have a staking set and the poising issue would not be resolved (i don't have a staking set or poising tool).

[Nucejoe]

22 minutes ago, Xilikon said:

It's not an aftermarket, it's the original A Schild package, hence the surprise.

I am not sure original A Schild package is a guarnty that Chrono grade is inside.

I would unpin the hairspring-stud and pin the new spring into it, if you think you want longer terminal curve, shape one on the new hairspring.

Poising anulare balance wheel in no easy task.

Good luck.

 

 

 

[JohnR725]

5 hours ago, Xilikon said:

I noticed that the GP 440 have the hairspring without a stem, just a long terminal curve and the balance cock have the "plates" to pinch the hairspring while the new balance have a stud attached

we really need a decent picture of your watch located above the balance. But as a guess your watch has a micro regulator adjustment which probably also adjusts the beat. His so they can get really really good timekeeping imprecision beats of the watch as a guess without seeing it.

Normally we would not recommend swapping the hairspring is but it might be easier just to swap the hairspring if you somehow lucky it might work probably won't but it would be worth a try.

Then for the wording of the link below I'm guessing the watches are identical except? Except yours has a fancy probably patented micro regulator where the other one does not. The problem with cutting the hairspring at the stud is if you find the hairspring is too short you're screwed but I guess is worth the try.

It really would be better if you can find somebody to put a new staff in

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk&Girard-Perregaux_440

3 hours ago, Nucejoe said:

Hairspring off of one might not produce the right beat with the other wheel.

You also degrade the perfect poise each balance complete already has.

yes the classic problem hairsprings are vibrated to each balance wheel with some minor exceptions. So swapping a hairspring from one identical watch to another isn't usually going to work. The poise probably shouldn't be an issue in except? If both watches are chronometer grade it may not be an issue but if there chronometer grade they spend way way more time making sure everything is perfect. This means conceivably they dynamically poise the balance wheel that is with the hairspring and call it in place and putting a different hairspring and call it would affect the poise but if you don't care about your chronometer grade then and you don't want to do it staff replacement which would be the best thing to do. Yes want to be real careful not to damage or destroy the original balance wheel in case none of this works because then the only option down the road would be to put a staff in and if you destroy the hairspring on the original you're going to be in big trouble.

1 hour ago, Xilikon said:

About poising, I thought it was done without the hairspring so the balance itself is supposed to be well poised ?

static poise without the hairspring dynamic poise with the hairspring both of them statically should be so close it really doesn't matter.

1 hour ago, Xilikon said:

The other way is to buy a balance staff but i don't have a staking set and the poising issue would not be resolved (i don't have a staking set or poising tool).

the poisonings not going to be an issue this is a modern balance wheel it have to try really hard the screw the poise up. So typically people will staff these they won't worry about the poise you just need a staking set and knowledge of how to get the old balance staff out without destroying the balance wheel and of course putting the staff back in and being careful of what everything exactly where you found it otherwise you are going to have a poising issue.

1 hour ago, Nucejoe said:

I am not sure original A Schild package is a guarnty that Chrono grade is inside.

one of the ways we get a clue about this kind of thing is if you look at the manufacturing information sheets that eta has. Chronometer grade they just took way way more time to make sure everything is perfect. But they're also conceivably will be material differences. The balance wheel metal could be different and they hairspring most definitely would be different. the problem with the hairspring being different if it is different like different metals then its characteristics will be different visually they could look identical but if they're not identical in you cut the stud off but you don't care about the stud anyway seem I would go for it might as well try it out. But there is a possibility that typically as we pointed out you can't swap hairspring users always issues and if the characteristics are dramatically different there will definitely be issues but short of putting a new staff on or swapping the hairspringis not much else you can do.

 

 

 

 

[Xilikon]

Thanks @Nucejoe and @JohnR725for the detailed explanations. To avoid confusion, here is the edited photo of both balance (added identification to differentiate which is which) as the reason is that on the old, the bottom pivot broke off :

As asked, here is the photos of the balance cock in all angles to show the regulator and such :

As you can see, it's not a fixed stud and when i unscrewed this stud screw, the hairspring just fell off like that so I think it's pinched between the brass plates. 

The new balance complete has a attached stud and a different terminal curve. The AS 1920 can be found on many high beat watches from Mido, Longines, Zodiac, Girard Perregaux and others. If we go to the website of a GP 440 disassembly and reassembly, we can notice the end of the hairspring going over the stud.

If I understand the implications well, the best course of action is to keep the original balance wheel and restaff it instead of trying to swap the hairspring to the new balance wheel ? If yes, it mean I must either buy a staking set or send it to a watchmaker to restaff it (main problem is that i don't know anyone willing to do that without requiring the whole watch to be sent for hundreds of dollars).

 

Edited April 30, 2021 by Xilikon

[Nucejoe]

If I correctly understand this, you have a broken pivot on GP440 shown above.

Best course of action is to unpin the hairspring from AS 1920.

Shaping the terminal curve of your choice on 1920 hairspring is a bit tricky. 

Note you do not want to remove the hairspring.

 

[Xilikon]

In the end, I think the best course of action is to restaff the original balance wheel. However, I don't have a staking set yet (it's in my plans but not ready right now) so I need to find someone who is willing to do that.

I tried reshaping the terminal curve on the new balance but then the problem is that the length isn't the same and there is no much room for the regulator pin. I reshaped it back to the original curve and put it aside (maybe for another AS 1920 or resell).