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strange behaviour with chronograph - is this acceptable?

Ilan
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Just notice today a strange issue - when I started the chronograph and the dial reached the 58th -59th second (of the fist minute to the count), it just stopped. Additionally the small dial @ the left hand side, (which counts the second of the current time) stopped!
I pushed the right upper pushbutton to stop the chronograph and reset – and the small left hand second counter continued counting time normally.
I tried to reproduce the issue – and it was reproducible!
Then I went on and wind the watch, since it was almost completely unwind (over 24 H for sure), re-tested and the issue wasn't reportable anymore!
Is this normal behavior when the "spring" is unwound ?
Background – this watch is an early 70s omega speed master, just returned from an overhaul repair @ Omega workshop.
Thanks in advance.
Ilan.
 
dsio
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Ilan
Just notice today a strange issue - when I started the chronograph and the dial reached the 58th -59th second (of the fist minute to the count), it just stopped. Additionally the small dial @ the left hand side, (which counts the second of the current time) stopped!
I pushed the right upper pushbutton to stop the chronograph and reset – and the small left hand second counter continued counting time normally.
I tried to reproduce the issue – and it was reproducible!
Then I went on and wind the watch, since it was almost completely unwind (over 24 H for sure), re-tested and the issue wasn't reportable anymore!
Is this normal behavior when the "spring" is unwound ?
Background – this watch is an early 70s omega speed master, just returned from an overhaul repair @ Omega workshop.
Thanks in advance.
Ilan.

It is normal behavior when the spring is unwound. Interesting reason why as well!

With a chronograph, lets say the power reserve is 42 hours. At 42 hours from last wind, what happens is the friction, or drag of the movement, overcomes the amount of torque that remains in the mainspring, at which point the movement stops. Lets say the amount of torque in the mainspring required to run the movement at this point is 1.0.

Now, if the chronograph is running, more gears are in motion, and the drag and friction of the movement is increased. This means it takes more torque in the mainspring to keep the movement running than it would if the chronograph was disabled. So lets say the torque required to keep the movement running with the chronograph engaged is 2.0.

Now at the point 41 hours after it was fully wound, the torque in the mainspring is, lets say 1.5. Now that means it is NOT enough to turn the chronograph as well as the normal movement, but it is enough to run the movement on its own.

So you were engaging and disengaging it in that grey area, near the end of its power reserve, causing it to stop when the drag became too high (engaged) and start when the drag was reduced (disengaged).

Give it a full wind and enjoy your watch my friend, all is good!

Post a picture too when you get a chance, Speedmasters are ALWAYS welcome here 😁
 
dsio
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It also means that if the chronograph is running, and you stop the chronograph 1 second before the entire watch would have stopped moving, it will continue for another hour or two afterwards.

However, its also why the chronograph being running or not has NO effect on an automatic staying wound, as the mainspring always exhausts its energy at a constant rate (28,800 vph in my case), and the chrono's drag only factors in if the mainspring is unwound at its limit.
 
Trev
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Hey Ilan. Welcome to the forum 👍
 
Ilan
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dsio
It is normal behavior when the spring is unwound. Interesting reason why as well!

With a chronograph, lets say the power reserve is 42 hours. At 42 hours from last wind, what happens is the friction, or drag of the movement, overcomes the amount of torque that remains in the mainspring, at which point the movement stops. Lets say the amount of torque in the mainspring required to run the movement at this point is 1.0.

Now, if the chronograph is running, more gears are in motion, and the drag and friction of the movement is increased. This means it takes more torque in the mainspring to keep the movement running than it would if the chronograph was disabled. So lets say the torque required to keep the movement running with the chronograph engaged is 2.0.

Now at the point 41 hours after it was fully wound, the torque in the mainspring is, lets say 1.5. Now that means it is NOT enough to turn the chronograph as well as the normal movement, but it is enough to run the movement on its own.

So you were engaging and disengaging it in that grey area, near the end of its power reserve, causing it to stop when the drag became too high (engaged) and start when the drag was reduced (disengaged).

Give it a full wind and enjoy your watch my friend, all is good!

Post a picture too when you get a chance, Speedmasters are ALWAYS welcome here 😁
Many Many thanks for your detailed answer !!!! I'll upload photos
Thanks,
Ilan
 
dsio
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Nice, Cal 861 from early to mid 70s?
 
Ilan
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dsio
Nice, Cal 861 from early to mid 70s?
Yes! it is cant date it exactly it was my late father's watch, i remember it ever since on my dad's wrist, I loved this watch since i was young....i started wearing it latelly so I'll always carry a recollection of my dad with me.
 
dsio
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If you're interested in finding further details, you can actually request information from Omega's Vintage Watch database

If you can provide them with the serial number they should be able to give you all the details on when it was purchased, and the exact reference etc.
 
Ilan
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dsio
If you're interested in finding further details, you can actually request information from Omega's Vintage Watch database

If you can provide them with the serial number they should be able to give you all the details on when it was purchased, and the exact reference etc.
I don't have its serial number, I asked Omega (while the watch was in the workshops) to try and locate it on the watch - they said that they couldn’t locate a S/N on the watch, strange.....
 
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