Long power reserve 5740C - can't understand how - Seiko & Citizen Watch Forum Japanese Watch Reviews, Discussion & Trading
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Old 03-25-2019, 10:30 PM   #1 (permalink)
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Default Long power reserve 5740C - can't understand how

I was worried my 36000 bph Lord Marvel LM36000 was not giving a proper power reserve after the last few times I wore it. It's manual wind only and since the plan is to wear it only 1 day at a time I guess I was underwinding.

So as a test, on Saturday night I gave it a major full wind. It quit tonight and ran for 46 hours and 7 minutes. I thought this was a normal 40 hour-ish main spring.

It just sat dial up not moved the entire time. So I am relieved that it was just me underwinding for 1 day's worth of rotation wear, but now I am curious.

Anybody know the proper power reserve on a 5740C movement? And how could it be that it could run an extra 6+ hours if it's the usual 40 hour PR ?

While we are at, anyone know the proper lift angle ?



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Old 03-25-2019, 10:36 PM   #2 (permalink)
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To answer my own question to spur discussion, Whineboy says his offers 48 hours Power Reserve. So that makes me think 46+ makes sense.


(Also a black dial like my own, quite unusual I have seen maybe 3 or 4 others over the years)




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Mine is 48 hrs. VERY stiff wind after about 15 turns.


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Old 03-26-2019, 12:53 AM   #3 (permalink)
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if only chhon's threads are as easily answered.
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Old 03-26-2019, 02:12 AM   #4 (permalink)
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It's a power reserve 'Marvel'
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Old 03-26-2019, 03:17 PM   #5 (permalink)
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Black dial is very Nice I have a silver Dialed and always wondered
or was concerned with fear of over winding. I think that is not posable. beautiful Black Dial.
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Old 03-26-2019, 07:35 PM   #6 (permalink)
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Quote:
Originally Posted by seikozen View Post
Black dial is very Nice I have a silver Dialed and always wondered
or was concerned with fear of over winding. I think that is not posable. beautiful Black Dial.





Apart from breaking the end of the mainspring a manual wind watch can't be "overwound".
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Old 03-28-2019, 09:56 PM   #7 (permalink)
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Jon,
This might be a fun one to dive deeper into, since it is a relatively simple movement to observe. If you can count the number of turns that the ratchet wheel makes to fully wind the watch (from being completely unwound), and then count the number of teeth on the barrel and the number of leaves on the center wheel, then you can calculate the theoretical power reserve of the caliber. Actual will be a little less because at low enough power the balance will not travel far enough to unlock the escapement. Here goes some mathematics, buckle up!

The 6105 barrel has 84 teeth, and the 6105 center wheel has 12 leaves on its pinion (which is turned by the barrel teeth). The 6159 barrel and center wheel have the same counts on its respective parts.
Since the center wheel revolves once per hour (it is what the minute hand is ultimately connected to), it takes 7 hours for the barrel to make one revolution (84/12=7)
The mainspring for a 6105 has about 7.5 turns to fully wind. So the theoretical power reserve should not exceed 52.5 hours (7x7.5=52.5).
But the mainspring for a 6159 has about 5.5 turns to fully wind (thicker and therefore stronger mainspring for the hi-beat escapement takes up more room in the barrel resulting in a shorter length). So the theoretical maximum power reserve on a 6159 should not exceed 38.5 hours (7x5.5=38.5). I've got notes here on a serviced one that achieved 37.883 hours, but that's only one data point, not something I'd claim as anything more.

If you'd like to play along at home, here's what I posit for the 5740C.
The 5740C barrel has 72 teeth, and the 5740C center wheel has 10 leaves on its pinion.
The mainspring for my 5740C has just over 7 turns to fully wind. So the theoretical power reserve on my example should not exceed 50.4 hours (7x7.2=50.4). How many turns of the ratchet wheel do you get from your mainspring, after completely letting the power down via the click, and then re-winding up fully? I am winding my mainspring fully at 9pm tonight (3-28), I'll get back to you in about two days with actual results.
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Old 03-28-2019, 10:30 PM   #8 (permalink)
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Noah you amaze. Thank your the lesson.


It's dead stopped now, I can let the main spring down a tad more via the click spring.


I will play around later tonight I can't spare the time.
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Old 04-01-2019, 10:34 PM   #9 (permalink)
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Follow-up: My first power reserve test on a recently serviced 5740C started at 9pm and two days later ended at 8:48. Because it was the weekend I was unable to verify AM/PM, but my second test suggests PM. The second test ran to right at 9:00pm two days later, giving me confidence to say that a ~48-hour power reserve can be expected from this caliber, which is 5% less than the absolute theoretical maximum (which as discussed could never be realized due to a minimum amplitude needed to achieving unlocking of the escapement).
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Old 04-01-2019, 11:47 PM   #10 (permalink)
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Thanks Noah !
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