• Tired of adverts on RWI? - Subscribe by clicking HERE and PMing Trailboss for instructions and they will magically go away!

Possibly a dumb question: swapping watch movements

ekg

Active Member
Supporter
Certified
6/2/12
408
53
28
I have 0 experience with opening watches and fiddling with them so please excuse if this is really stupid. I recent bought the JF 116680 and on day 1 the small seconds hand was moving very shitty. Almost getting stuck. Not even close to smooth. 14 minutes later it got stuck. I sent it back for repair and the video I got showing it was repaired was less than great. Again not moving smoothly at all. Not sure if it’s the 7750 movement or what.

On the other hand I have an arf 116500 with the 4130 movement which has been a perfect rockstar. The question is, is it possible to just buy a 4130 movement and put it jnto the 116680? Aside from the case sizes being different, it’s the same functions. Thoughts?
 

KJ2020

Time Traveler
Supporter
12/3/18
32,286
56,401
113
The SA4130 movement would not be cheap if you could source it at all. I saw one listed on ebay once for about $400, and I had a TD quote me $350 for one IIRC. I think you would be better off sourcing another A7750 or send this one to a US watchmaker when you get it back. The native position for running seconds on a 7750 is 9 o'clock. The Chinese use transfer plates and other jury rigging to move the running seconds to where it needs to go for the model. There are a number of 7750 variants with different subdial features and layouts, but AFAIK none of them have running seconds anywhere but at 9 o'clock.

https://www.watch-wiki.net/index.php?title=Valjoux_7750
 

ekg

Active Member
Supporter
Certified
6/2/12
408
53
28
I don’t mind the cost, I’m trying to replicate an $18k watch so spending $400 to make sure it somewhat looks like one is ok in my book. I looked into the 7750 movements but they all appeared to be chronographs and had seconds in wrong position.

So so aside from the cost, is there any reason the 4130 wouldn’t work?
 

KJ2020

Time Traveler
Supporter
12/3/18
32,286
56,401
113
I don’t mind the cost, I’m trying to replicate an $18k watch so spending $400 to make sure it somewhat looks like one is ok in my book. I looked into the 7750 movements but they all appeared to be chronographs and had seconds in wrong position.

So so aside from the cost, is there any reason the 4130 wouldn’t work?

There would be some modding needed to remove the pinions or wheels on the totalizers at 3 and 9, and maybe a different movement holder IDK if there are size differences. Something else you would need to know before committing to this is whether the stem height of the 4130 will be compatible with the 7750 case and I don't know that answer, it would need to be researched or someone else who knows might chime in.

Stem height is the distance between the center of the movement stem hole and the back of the dial. It's critical because if the stem doesn't fit in properly it would have stress on it from an vertical component. Mods can be done to offset this issue to a degree. Like using an extra dial spacer to lower the movement or redrilling and replacing the tube, etc but you can see the swap may not necessarily be a 1:1 swap and go.

The stem height issue becomes more interesting in a chronograph because of the pushers.

And you'll still end up with a rep that doesn't fully function like the gen, the Regatta feature is frozen. But a lot of us have poured money into watches because we wanted to and we can so go for it. Nothing wrong with having a great movement in a watch you love.