Decasing the movement for a Girard Perregaux Gyromatic High Frequency 9377GA

[Xilikon]

After waiting for months for the watchmaker to return me (I requested the return as he took too long to bother looking at mine since last summer), I finally got it back so I proceed to start disassembling but I got stumped a bit with that watch when it come to removing the movement.

I removed the back which is screwed and removed the antimagnetic shield, I see the movement fine so I removed the two screws holding it to the movement ring. However, the ring is firmly set in the case with what seems like hard rubber pieces between the groove (look like this <o>). I figured out it might be because the movement needed to be turned a certain way to remove it. Since the stem look "broken" without crown, I tried to remove the stem and disassembled the movement enough to access the winding parts and used a knife to slowly pull the stem out of it.

Upon removing the stem, I noticed it is not broken but a split stem so it was a surprise (if there is no caseback, i would know but with a caseback, i thought it was a standard one). I guess this mean the movement is front loading ? Guess I need to figure out a way to pop the crystal out. I tried turning but there is no way it can get out.

[watchweasol]

The fact that this has a split stem would lead one to think it was in deed a front loader. The watch was based on the AS 1687/1688 according to Ranfft but no tech sheets for that caliber has as yet been found.  Dates from around 1960.   Looking at the picture of the front of the watch there looks to be no provision for removing the bezel, so with that in mind a close inspection of the sides of the watch for  the indent or marks from a previous entry  

[watchweasol]

There is also the possibility that it would require the glass to be removed using a glass pump as is the case with monocoque cases.

[Xilikon]

7 hours ago, watchweasol said:

The fact that this has a split stem would lead one to think it was in deed a front loader. The watch was based on the AS 1687/1688 according to Ranfft but no tech sheets for that caliber has as yet been found.  Dates from around 1960.   Looking at the picture of the front of the watch there looks to be no provision for removing the bezel, so with that in mind a close inspection of the sides of the watch for  the indent or marks from a previous entry  

Actually, it's based on AS 1920 as it is a high beat movement with 36000 bps. 

 

I finally managed to decase it... The movement ring was held by 'rubber' pieces all around (that's why there is a slot on the movement ring to insert those pieces) but being dried and struck, the only way is to try to pry the ring out of the case and working around until the pieces get loose enough to be removable. It is like a kind of lateral shock protection. The split stem seems not original to this watch because it is definitively not front-loading so I will replace it with a normal stem as part of the servicing.

A fellow watchmaker mentionned this ring mounting method is also used on certain Omega watches.

[watchweasol]

Well done  peculiar that it had a split stem.  Did you find a tech sheet for the AS 1920 ?

    

[Xilikon]

13 minutes ago, watchweasol said:

Well done  peculiar that it had a split stem.  Did you find a tech sheet for the AS 1920 ?

    

Not really a tech sheet but I do have a parts list. 

By the marking in the back, last servicing is 22-10-86 and I guess the watchmaker did not do a 100% good job with this one given a few modifications (the dial has 2 holes for the feets when originally, there should have none).

2509_AS 1920.pdf

[watchweasol]

Thats all the tech info I could find as well.  That method of filling dial feet was common before the invention of the dial foot soldering machines of today

[killerfred3000]

I've got a girard perregaux AS 1187/94 from the 1950s and it also has a split stem.  Maybe your stem was original?  Does anyone else have experience they can contribute?

See below: