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Clocks, Watches/Adjusting a Hermle movement


QUESTION: Hello, I have a Franz Mermle 2 jewel movement model number 1050-021 and it runs fast. I have tried adjusting it by turning the screw directly above the stamping on the back plate that shows adjustment for speed I believe. It shows a screw head with a plus on the left and a minus on the right with a triangle below each sign, I have turned the screw the direction that it seems to indicate would slow the movement ( clockwise ) and the clock sped up. I then turned the screw counter clockwise and the clock continued to speed up. Am I turning the proper screw, it turns a shaft with threads on the outside and that in turn moves a small plate on top of the movement that has the end of coil spring attached. If so why would it speed up no matter which way I turn it and if this is the wrong screw how go I adjust the speed of this clock? Last; is there a way to stop the clock from running so that I can set it to the correct time? Thanks Jim


This is not so easy to explain or fix via internet talk.

You are probably turning the correct screw. The way it works is
the more hairspring that is turning the slower the clock runs. The less spring
that is turning the faster it runs. So when you turn that screw see if
the lever on the spring is making the spring longer or shorter.
You want the spring to have a longer length so it takes more time to complete
it's rotation.

If the mainspring is running low, like at the end of the 8 day cycle the
clock can run faster due to lack of power allowing the hairspring to complete
it's full rotation.
So when adjusting the clock make sure it is fully wound within  3 days of winding.
That will be enough spring strength to keep full power for full rotation of the hairspring.
However at the end of the 8 days it may normally run a bit fast.

The clock may need oil, or a cleaning or the clock can also be worn out depending on
how many years the clock has been running. Sometimes the mainsprings are so gummy
they need to be taken out and cleaned and regreased.

You don't have to stop the clock to set the correct time. Just set the time
and the clock has a built in adjustment that will correct the striking and chiming
of the clock within 2 hours.

Those hairspring adjustments test our patience. If you have any oil on the
hairspring it will stick together and cause it to run fast too.

Hope this helps,
The Clocklady

---------- FOLLOW-UP ----------

QUESTION: Hello Marilyn, Thanks so much for your reply the answer was quite helpful. I should let you know this is a new movement, and so should not need oil or cleaning, I just want to make sure that moving the hands backwards won't hurt the clock mechanism, the clock does seem to be slowing down a bit as I have the screw turned as far as it will go in the indicated direction. Thanks again. Jim

If the screw is turned as far as it can turn you can look at that piece on the hairspring. Can you move that so that more spring will be moving? Sometimes they can lift up and move manually.

Many clock manufacturers suggest moving the hands backwards. This is for new clocks, not the antique clocks.


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Marilyn Bellotti


This is for advice only. ~Most~ repairs need a professional. If I can help you with an adjustment that can set your clock back in order I will try. I can not write a chapter on clock repair. I will point you in the right direction and you will have to do your own research on how clocks work for more intense repairs. -No Watches -No Appraisals. Search ebay for past sales for that information.


29 years repair experience

Certified Horologist

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