This is my first time posting on this sight. I will appreciate any insight into this issue.
As the title states, I have a 1968 Omega Seamaster chronograph 145.018. I purchased this watch from Jackmondwatches in November 2016. The watch had a service before sending it to me. I feel confident it was actually service based on the time grapher numbers. On a full wind amplitude is 301, beat error 0, and rate -1.
With the chrono running amplitude is 285, beat error -1, rate -4.
The issue: The watch will run perfect without the chrono but, with chrono engaged it will randomly stop. It may run 2 hour or it may run 20 hour before it stops. If I stop and start the chrono it will start running. I have even tapped on the crystal and started it back running. Strange thing, time is random but the chrono sweep always stops at 58 seconds. None of the hand are touching.

Jeff

 

The watch is stopping as the finger on the central chronograph seconds recording wheel is tripping the minute recorder function - this is the seconds recording wheel and the arrow is pointing at the finger:



If the amplitude is as high as you say, then I would be looking at the tension on the spring for the minute counter jumper, on the underside of the chronograph bridge.

The finger on the wheel above contacts an intermediate wheel for the minute recorder, and then the minute recorder wheel. The minute recorder wheel is kept in place buy the minute recorder jumper:



It moves out of the way to let the wheel advance, and the tension of that is controlled by the spring:



You adjust the tension of the spring by rotating the block it's attached to at the red arrow. It would be more likely to stop the watch if the power has run down, so although you mention that sometimes it stops quickly, and sometimes runs for hours, that is in relation to when you started the chronograph, not how fully wound the watch is - this might not be as random as you think.

So you could experiment to find out from a full wind if the watch runs longer before stopping than it does say 24 hours after full wind.

To me this is the most plausible reason for the issue you are having, and it goes back to the quality of the service that was done. Omega requires that several items they refer to as chronograph controls are checked during a service, and the tension on this spring is one of them. I make a point of letting the chronograph run for at least 24 hours after doing a service to make sure things like this don't happen, but not everyone does.

Cheers, Al

 

Interesting, as my 861 speedy is doing a very similar thing. However, my chrono seconds hand doesn't always stop at 58, it can stop randomly at different places. Sometimes it will run for an entire day, sometimes it will stop within 30 seconds of starting.

I suspected it might be related to how wound the mainspring was as well, but haven't yet found a correlation. I, however, know that my speedy does need to be serviced.