Denes_Papp
160
Breguet surgery
One of my favorite watch is a Breguet XXI, Ref 3817. It is a flyback chronograph with a center minutes hand.
The movement in this watch is Breguet calibre 584Q/2, a very robust and reliable cam switched horizontally coupled chronograph, related/based on the historic Lemania 1340/ Omega 1040 automatic ebauche from the seventies.
The story of the Lemania 1340 and its successors is an enduring portrait of the twists and turns of the Swiss watch industry. (One day to put this story to ink 
I have great fondness for center minutes counter chronographs, the layout makes for an extremely legible and intuitive read of the elapsed time. This arrangement is exceedingly rear, and in the family of integrated automatic chronographs even rarer.
This chronograph utilizes a horizontal clutch. And herein lies the rub!
A horizontal/lateral clutch inherently demonstrates a certain level of jerkiness of the seconds hand upon starting the counting function. This tremor or jump that occurs when the chronograph is engaged, is caused by the uneven number of teeth on the coupling wheel and the seconds wheel. The amplitude of the “jump” is random and can be barely visible or fairly obvious.
Here is a video of my Breguet XXI, you can observe the chrono seconds hand jumping on start from 0.1 sec to almost 0.5 seconds:
https://youtube.com/shorts/YMUD-vgE_Dk?si=qLxlxPKCnaMI8PFi
I am not going into differences between horizontal vs vertical vs tilting pinion. I leave that topic for a further discussion.
At the beginning of this year I came across an image of the Breguet Marine chronograph that uses a variant of the 58x series of movements, the 582QA. This movement uses a LIGA process chronograph coupling wheel.
Please see my previous post on this:
Since the back side of the 58x movements are identical (with different finishing patterns, but everything else the same) an idea was planted in my mind, that I just could not shake out of there.
What if I just switch out the standard chronograph coupling wheel with the LIGA wheel?
I know some of you might consider this idea sacrilegious or even stupid and even might accuse me of creating a “franken” watch, but I just could't not to trying this out.
Here is my XXI opened up on the “operating table” in its original state, sans the rotor.
This wheel is a stacked one with same teeth profile, but different number of teeth (60/80).
It is very hard to take good images with my poor man's photo equipment, and the wheel is also very shiny.
This is my best closeup image, but you still can see the unique teeth arrangement.
Despite the fact that there are two stacked wheels, the overall height is the same as the original coupling wheel.
It made things much cleaner since I didn’t have to switch the wheel bridges. And looks clean since the other one is matt black.
I could not get away not changing the Chrono driving wheel though. The lower wheel sits at the original level of the Chrono train, and meshes with the Chrono seconds wheel. The top wheel sits above the original gear train height, therefore I needed the Chrono driving wheel from the 582QA. It has only four spokes, much like a “traditional Breguet” wheel.
"Postoperative" picture:
I adjusted the meshing depth of the teeth of the driving and top coupling wheel. I used the recommendation from the Omega 1040 service manual that recommends 2/3 depth of the driving wheel tooth length.
https://youtube.com/shorts/oshO-WIxJ-4
And a closeup of gear meshing:
The chronograph runs well, I am currently checking accuracy in different positions. As of yet 1.2sec/day.
Denes
Breguet surgery
Appreciate? Definitely not!
Thank you for this interesting post and helping me decide it was time for my Boucheron to take a rest and my Breguet Type XXI 3810ST to come out to play.
