Balance Complete Size Interchangeability

[dralexmv]

I am unable (can't find it) to source a replacement for a FEF 380/381 Balance Complete and was wondering if I could use another 11.5 (or even 10.5) lignes movement's balance complete as a replacement. What are the pro's/con's of doing this sort of franken-work. I know back in the day this practice was not frowned upon as much as it nowadays, but with a dwindling supply of parts I don't see what other options we hobbyist have.

[wls1971]

There are a few on ebay:

https://www.ebay.it/itm/Balance-complete-F-E-F-FEF-FLEURIER-350-380-380-2-bilanciere-completo-721-NOS-/162699375077?hash=item25e1a371e5

This seller has incabloc version or kif version for sale,

6 hours ago, dralexmv said:

wondering if I could use another 11.5 (or even 10.5) lignes movement's balance complete as a replacement

If you mean take a balance from another FEF 380 donor movement yes, but if you mean taking a similar size movement of different manufacture and using that then no I would not think so there are just too many variables to list to make it a option.

[clockboy]

8 hours ago, dralexmv said:

I am unable (can't find it) to source a replacement for a FEF 380/381 Balance Complete and was wondering if I could use another 11.5 (or even 10.5) lignes movement's balance complete as a replacement. What are the pro's/con's of doing this sort of franken-work. I know back in the day this practice was not frowned upon as much as it nowadays, but with a dwindling supply of parts I don't see what other options we hobbyist have.

The problem will be the balance staff will be most likely the wrong length. I have in the past used the a hairspring from a different calibre. Providing the hairspring is for a watch that is of the same Ligne and the hairspring has the same end stud style it works fine. 

[rodabod]

You can use a smaller balance complete as long as the correct staff fits, and you manage to get the terminal curve of the hairspring to work with the correct radius so that it is centred between the curb pins. 

[JohnR725]

On 3/7/2018 at 2:50 AM, rodabod said:

You can use a smaller balance complete as long as the correct staff fits,

A small amount of change shouldn't be a problem but if you get really creative and go super small then they'll be a consequence. The hairspring has another characteristic that you normally don't think about which is it supplies the energy to unlock the escapement. So if we got super creative and put a really tiny balance wheel in the watch it just wouldn't work at all or somewhere in between it may not work very well.

So when adapting a different balance wheels as mentioned the staff will need to be changed. Also the roller jewel has to be a the right size and in the right location. Then the safety roller also has to be right otherwise you're going to have to change the guard pin length.

Now we get to all the strange things about this watch like for instance two separate balance staffs you learn that at the link below the reason given is "balance with/without screws". Bestfit also lists two separate staffs and two separate balance completes I have The balance completes listed below. Then the size of this watch is interesting the 350 is 10 1/2 line and the 380 is 11 1/2 line. I suspect both watches are probably identical except a larger plate for the 380. It would be a way for a company to have two separate watches without having to manufacture entirely two separate watches.

721/268

DOX 140      PES 380
FEF 350      DIRECT CENTER SECOND
FEF 380      DIRECT CENTER SECOND
FEF 380-2    DIRECT CENTER SECOND CALENDAR
PES 350      DIRECT CENTER SECOND
PES 355     
PES 380      DIRECT CENTER SECOND
PES 385     
ROL 380-2

721/269
BALANCE COMPLETE
INCA/FEF 350

DOX 140      PES 380
FEF 350      DIRECT CENTER SECOND
FEF 380      DIRECT CENTER SECOND
FEF 380-2    DIRECT CENTER SECOND CALENDAR
PES 350      DIRECT CENTER SECOND
PES 355     
PES 380      DIRECT CENTER SECOND
PES 385

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk&FEF_350

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk&FEF_380