I put this in vintage help, but I am aware that some of you will not consider this exactly vintage. Ok, so I recently had a great transaction to purchase this watch from a Forum member, and I am not looking find fault with the seller I love this watch and factored in a service at some point. I noticed an issue with the chrono hand, and other people observing my watch have noticed this. I have already discussed this with the seller, and he fully described the watch and service history to me prior to purchase and I feel he has zero responsibility on this. I had the watch checked and was told the amplitude and timing was good and it did not need a service (they had it 5 minutes and did not pop the back) before I noticed this issue, and no I did not get a sheet and I am not super confident in them. The watch keeps time within 3 seconds a day, with or without the chrono running. I ran it for 2 days with the chrono in sync with the small second subdial, and there was no change in accuracy. What appears to be happening is the chrono hand lags every few beats then jumps to catch up. It is noticeable at full speed in front of you, and I do not notice it on any of my other non speedy pro chronos. What I have is a slow motion video that captures it, I tried to take a full speed video but camera shake seems to make it disappear. I can try to take one if people think it will help. In this video watch the jump on the chrono hand between 11 seconds and 12 seconds 40 seconds into the video, there is a clear beat where the small sec moves as normal but the chrono hand misses then jumps forward. Yes I know the video is upside down, I heard some of you guys in Australia are the real experts so I decided to make it easier for you Here is a full speed video where you can notice it esp in the first 20 seconds, and again between 40 and 44 seconds on the watch. It is more noticeable in person.
We'we had this issue on the german watchforum too. I observe the same on my speedmaster but not as obvious as on yours. There are two gearwheels involved in driving the stopsecond hand and there always has to be a backlash so the gearwheels don't get stuck. An adjustable spring is minimizing the backlash but on adjusting it you have to find the right amount so it is not too tight (watch will stop) and not too loose (a lot of backlash). When the gearwheels are older and probably worn it may be hard to get the tension of that spring right. It does not affect the overall precision of the stopsecond hand. Cheers Thomas
I have seen this "stutter" before, in the 321 and a couple of other references as well. In each instance, it was on chronos with a longer chrono sweep and a "heavier" tip, but that's probably just coincidental. @Archer Is it an "easy" adjustment, or does it affect other functions?
Easy to adjust, as the spring can be removed and installed without any real disassembly (other than removing the case back and inner cover) but of course adding friction can have other implications. You have to be careful as adding too much friction can cause an unacceptable amplitude drop when the chronograph is engaged. Cheers, Al