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Old 3 December 2017, 05:04 AM   #1
DKS2375
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GMTII C Timekeeping Question

I have a GMT II 116710LN purchased new in April of this year. It keeps time consistently at +/- 2 sec per day worn in an office setting. However.....I've noticed that if I wear it to the gym or during an activity with quite a bit of wrist movement it will suddenly gain 10-20 seconds for that day. The next day it will settle back to +/- 2 seconds.

Any ideas why this occurs? Should I send it in to the Dallas RSC to be looked at under warranty?

Thanks so much in advance for any ideas or advice.
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Old 3 December 2017, 05:18 AM   #2
Heff
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Doesn’t sound normal to me. My Exp II runs about .5-1 seconds faster per day when I am more active. But normally it is +1.6 spd. I would have it looked at.


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Old 23 December 2017, 01:20 PM   #3
NIHO
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Possibly Overbanking

HI,
I just posted this issue on the watch that gains 60s/day when worn. This is likely "overbanking". I had that on a watch and the RSC eventually had to replace the entire movement. In our case, it may just be excessive movement and jarring the watch. My GMT IIC has been keeping COSC +/- 1s/d for many years. If I jog, it may gain a stray second or two, but it never does when I play tennis, light weights, etc. If yours is very sensitive to movement, the mainspring may be overwinding, something called overbanking. Ask the RSC and see what they say.
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Old 24 December 2017, 01:00 AM   #4
SearChart
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FYI: 'Overbanking' is when the mainspring is a little too powerful, and the constant winding due to the rotor causes the amplitude to reach unacceptable levels.

A 3135 is allowed to have a maximum amplitude of 300degrees, if the spring is too strong for some reason it can reach up to 340degrees, which is when the impuls jewel (red in the drawing) slams into the outer sides of the pallet fork(marked green).

This causes erratic timekeeping.
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Old 24 December 2017, 03:25 AM   #5
unreformed66
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If your hearing is good enough, hold your watch up to your ear after doing your strenuous activities or manually winding it 40 or so turns so that it's wound to it's maximum potential. If you get the regular ticking sound it's probably not overbanking. If it sounds like a horse galloping or a rythmic knocking sound then it most probably IS overbanking which as previous posters mentioned will cause erratic timekeeping. A timing machine will show overbanking as well. If it's under warranty I'd send it back for them to have a look at. It could be as simple as the mainspring being incorrectly greased which will cause it to build too much tension before "slipping" as it is designed to do to limit the tension.
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