Watch repair is an interesting life, more often that not it is like the repair of anything mechanical, there is normally a symptom to be addressed, but we also need to find the cause.
This watch was presenting itself with an interesting and annoying issue that it was breaking the screws that were securing the chrono operating lever (part no. 8140), this in turn meant that the chronograph would not function and there was a screw stuck in the chronograph mechanism plate. (Part no. 8281)
Upon inspection there was obvious play in the operating lever, and this was the result of an elongated hole, but I also thought that the locator on the plate may be worn as well – so since they were available decided to replace both parts.
Once the watch was reassembled I examined the functions of all the chronograph parts and the issue appeared to be as follows:
The flyback lever (part no. 8180) was not operating properly because the spring on it was slightly out of shape. This had meant the end section that operates the chronograph movement hammer was not falling into place.
As this had started to occur the previous owner would be able to start the chronograph, but stopping it would become harder and harder, probably the owner had then pushed harder and harder to stop it and reset it, and over time caused the wear and tear.
Rather than replace the part with the misshaped spring it was simple to take it off and bend the spring back into place, this put the correct pressure back onto the floating end piece so that it located properly.
For now though – all is good for the watch and chronograph functions of this beautiful movement.