Is it a defect on a new Speedy 3570.50….?

That's not normal. This is a detail I never paid close attention but just played with mine and the second hand does not budge backwards like yours when activating the chrono function. I know it sucks to have a brand new watch with problems but the good thing is that the warranty will take care of it - is probably a simple fix/adjustment.

I don't believe this is a coupling issue, because it appears that the hand moves before the coupling clutch would be engaging with the chronograph runner.

First and simplest thing to do is to have the watch demagnetized. As the hammer lifts off the cam on the chronograph runner, if either have a bit of magnetism it can cause the runner to move before the coupling yoke moves to engage the chronograph. Also heavy oiling on the cam or hammer can cause this.

There are other more involved things that can cause this as well (contact between the hammer and main wheel of the chronograph runner as the hammer is lifting is one example), but demagnetizing is the simplest thing to try and is non-invasive.

Cheers, Al

Good deal! Two new watches in a short time! 👍 and welcome to the Club! 😜

I have some appointments but if I get time today I'll post an example of this issue I came across yesterday...

So this is a Speedmaster that exhibited the same symptom yours did - the central seconds hand for the chronograph would turn backwards slightly when the start button was depressed. As I was troubleshooting this, I saw that the chronograph bridge was bent slightly - this photo shows it, but the bend was actually much worse when you looked at it first hand:



The left side of that red line that I added is where the bridge is at it's thinnest, and that is right over the chronograph runner that has that hand attached. It was likely bent by someone prying on the bridge in this location to remove it at some point.

So I took a video of the issue from the movement side. Note that the chronograph runner is pretty much in the center of the frame, and on top of that is the hammer - this is the part that resets the chronograph seconds and minutes when you hit the reset button, and it holds those 2 counters in place when the chronograph is reset.


As I press the start/stop button to start the chronograph, you can see the chronograph runner turn in one direction as the hammer lifts off, and then when the coupling yoke on the left engages, it starts turning the correct way. As I've mentioned, this can happen due to heavy oiling on the hammer or cam of the chronograph runner (surface tension causes them to stick), or if these parts are magnetized. But in this case, it's that bent bridge that is causing the problem.

With the bridge bent up at the jewel for the chronograph runner, the friction spring that is under the chronograph runner (the one that keeps the hand from stuttering) is pushing to chronograph runner up higher than it would be normally. This is allowing the runner to contact the hammer just slightly. When I press the button and the hammer is coming off the cams, it is dragging on the central wheel of the chronograph runner, and since at that point nothing is holding the runner in place, it is freely spinning. Then the coupling yoke comes in and the wheel is engaged.

Simply straightening the bridge solved this problem, but it could also happen due to a bent hammer (bent down to touch the runner) or even a jewel for the runner that is set too high in the bridge.

I know you were looking for something very specific to let others know what the problem with your watch was, but I think you should understand that problems like these can have several different causes. With your watch being new, I would not expect it to be happening because of a bent bridge like this one, but more likely due to magnetism.

I hope this helps show that there is not a single reason for most problems happening - you have to understand how the mechanism works, and look at it carefully to diagnose a problem like this one.

Cheers, Al

Close - the only error is that the part you have as the hammer is the brake. Part 2 in your diagram is the hammer.

Just for your interest, part 1 is the driving wheel for chronograph, and part 3 is the minute recorder runner.

So if you watch the video again, as the hammer lifts off the 2 runners, the chronograph runner turns slightly. It doesn't look like much here, but when you think of the length of the hand on the dial side, it does not take much movement here to make it look very big at the end of the chronograph seconds hand.

Glad you all found this interesting. The act of taking a watch apart, cleaning it, putting it back together, lubricating it, and doing some basic timing is in reality not all that complicated. The skills are pretty basic for a watch that does not have problems. When you have bad timekeeping, low balance amplitude, or something odd happening in a chronograph like this situation, that is where the ability to diagnose a problem correctly and fix it comes into play, and that is where a lot of the real skill lies.

Cheers, Al

If it just started, then likely it's magnetism - I would try having it demagnetized.

Cheers, Al