Can an old mainspring be the main reason for low power reserve in automatics?

Kargol · Apr 27, 2021

Hi guys and ladies,

My watchmaker told me this wonderful thing below, which I had never thought of, and decided to share:

“Imagine that the spring has tightened after so many years. It does not have the same elasticity. When you wind it, you use force and wrap it. The automatic does not have the power to wrap it if it does not have elasticity”.

Thoughts?

Canuck · Apr 27, 2021

There can be many causes of low power reserve in an automatic. If you quoted the guy exactly, it sounds to me like a bunch of malarkey. I think you need to have someone else check out the watch.

Dan S · Apr 27, 2021

I do think that an aged and fatigued mainspring can reduce power reserve in any watch, but the quote from the OP's watchmaker is not making sense to me.

It seems to me that if you have an auto-winding watch that is stopping, you would want to run some diagnostics to determine whether the issue is truly power reserve (one could test that by manual winding, if the watch allows it) vs. lack of efficiency of the auto-winding mechanism. In my mind, the second doesn't really fall into the "power reserve" category.

N05J3W3 · Apr 27, 2021

Yes. That makes sense. The mainspring stores energy, and then releases it. If its ability to store or release is impeded [fatigue, contamination, lack of lubrication] then performance suffers.

But very few of us get excited about mainsprings, do we?

SkunkPrince · Apr 27, 2021

N05J3W3
But very few of us get excited about mainsprings, do we?

I do! Change that thing at every service!

Kargol · Apr 28, 2021

Reading your replies I am a little confused. I am not a watchmaker but I think that there is logic in the quote of my watchmaker.
I guess the main spring gets harder and harder when years are passing. You may wind the watch manually with the crown and you see a full power reserve, however when you just wear the watch the circular mechanical power transferring from the automatic rotor to then mainspring may not be adequate to give a proper tension to “wrap” the spring. I can see the logic but would like to ask for more feedback from you.

JimInOz · Apr 28, 2021

This is a very basic explanation from me.

A "new" mainspring would be a completely straight and flat strip of metal
It is then given arbor hole/bridle etc and "curved" to form a loose coil we know of.

As that coil is tightened and loosened (winding/unwinding) over time, the spring loses its elastic properties and becomes more of a condensed coil, and this results in a shortened "power reserve" as the coil does not unwind to the full extent that it did when new and is not pushing against the barrel wall as hard as a new spring would.

So, when an auto winder starts winding an old spring, there is very little resistance and while the auto works turn the spring, it's not putting in much power.
The auto winder continues to wind until the bridle slips against the barrel wall, and that is now at full wind, somewhat less energy stored compared to a new spring.

A new spring will need a lot of turns to compress the coil until the bridle slips.

A tired spring will not need as many turns before it slips. Therefore the loss occurs due to loss of elasticity in the spring. Not work hardening.

Kargol · Apr 28, 2021

JimInOz
This is a very basic explanation from me.

A "new" mainspring would be a completely straight and flat strip of metal
It is then given arbor hole/bridle etc and "curved" to form a loose coil we know of.

As that coil is tightened and loosened (winding/unwinding) over time, the spring loses its elastic properties and becomes more of a condensed coil, and this results in a shortened "power reserve" as the coil does not unwind to the full extent that it did when new and is not pushing against the barrel wall as hard as a new spring would.

So, when an auto winder starts winding an old spring, there is very little resistance and while the auto works turn the spring, it's not putting in much power.
The auto winder continues to wind until the bridle slips against the barrel wall, and that is now at full wind, somewhat less energy stored compared to a new spring.

A new spring will need a lot of turns to compress the coil until the bridle slips.

A tired spring will not need as many turns before it slips. Therefore the loss occurs due to loss of elasticity in the spring. Not work hardening.

I think, now I get it!

Thanks my friend. Good explanation!

Dan S · Apr 28, 2021

Kargol
I guess the main spring gets harder and harder when years are passing.

I suspect there is a language barrier, but if you are suggesting that the mainspring gets stronger with age, then I think this is where the misunderstanding lies. Think about your experience with other types of springs. They don't generally get stronger as they get older. They fatigue with time and are less prone to return to their original shape when unloaded.

Archer · Apr 28, 2021

Can I ask in what context the statement was made by your watchmaker? Calling it the "main" reason for a reduced power reserve is not something I would agree with at all.

Jim has given a pretty good description of what you commonly see with the older blued steel mainsprings - over time they do lose elasticity and become "set". They also suffer from a number of other issues like rust, and breakage as they become brittle over time (possibly hydrogen embrittlement). This is generally not a big issue with modern alloy mainsprings though.

The mainspring is sort of one side of the equation in the run time of the watch - it's the power side. The "main" reason for a reduced run time is more on the load side of the movement - friction in the movement from old oils, dirt, worn parts, etc.

Cheers, Al

Kargol · Apr 28, 2021

Dan S
I suspect there is a language barrier, but if you are suggesting that the mainspring gets stronger with age, then I think this is where the misunderstanding lies. Think about your experience with other types of springs. They don't generally get stronger as they get older. They fatigue with time and are less prone to return to their original shape when unloaded.

Yes that’s what he meant. I am sorry I did not translate it right. I should say stiffness.

Kargol · Apr 28, 2021

Archer
Can I ask in what context the statement was made by your watchmaker? Calling it the "main" reason for a reduced power reserve is not something I would agree with at all.

Jim has given a pretty good description of what you commonly see with the older blued steel mainsprings - over time they do lose elasticity and become "set". They also suffer from a number of other issues like rust, and breakage as they become brittle over time (possibly hydrogen embrittlement). This is generally not a big issue with modern alloy mainsprings though.

The mainspring is sort of one side of the equation in the run time of the watch - it's the power side. The "main" reason for a reduced run time is more on the load side of the movement - friction in the movement from old oils, dirt, worn parts, etc.

Cheers, Al

Hey Al,
Well I don’t know why but he doesn’t always change mainsprings when he services my watches unless I tell him so, so it was my mistake mostly. He serviced and oiled the watch, checked that everything was ok when he put the parts back together. When I received it I noticed that although I wore it for a full day of work (my work includes a lot of moving and climbing stairs etc so it’s not a desk work), it stopped after 8 hours when I took it off and placed it next to my bed. I woke up in the morning and it was stopped. when I was complaining the next morning, he told me this about stiffness and that he must open the watch again and change the mainspring.
Well , this thing with the power reserve happened to me before and we didn’t service the watch . We only cleaned the automatic parts at that time and it was perfect. It is mostly my mistake because I forgot to tell him to order a mainspring and just charge me more. He has told me many times that parts are not included in the price of his service .

JwRosenthal · Apr 28, 2021

Replacing a mainspring is SOP during a service, wether it needs it or not. It’s like doing the clutch on your car when the transmission it out for something else- just worth doing it since you are there.

Kargol · Apr 28, 2021

JwRosenthal
Replacing a mainspring is SOP during a service, wether it needs it or not. It’s like doing the clutch on your car when the transmission it out for something else- just worth doing it since you are there.

Yes of course . I forgot to ask him though … as I said earlier he has told me before to tell him to change it so he can charge me accordingly

JwRosenthal · Apr 28, 2021

Kargol
Yes of course . I forgot to ask him though … as I said earlier he has told me before to tell him to change it so he can charge me accordingly

I hope he doesn’t charge you more to take it apart again. An 8 hour power reserve is something he should have caught before he let it out the door and advised it needed replacement. I get if he thought the mainspring was fine and got 45 instead of 48 hours out of it, but 8 hours- yikes.
Perhaps in the future you should just make a standing policy with him that all watches get a mainspring, any wear parts that are out of spec you will happily pay for replacement, and if it’s not 100% at the time of his final assembly, to call you and discuss.

Kargol · Apr 28, 2021

JwRosenthal
I hope he doesn’t charge you more to take it apart again. An 8 hour power reserve is something he should have caught before he let it out the door and advised it needed replacement. I get if he thought the mainspring was fine and got 45 instead of 48 hours out of it, but 8 hours- yikes.
Perhaps in the future you should just make a standing policy with him that all watches get a mainspring, any wear parts that are out of spec you will happily pay for replacement, and if it’s not 100% at the time of his final assembly, to call you and discuss.

Yes that’s exactly what I am going to do.
However the mainspring with manual winding had more than 40 hours reserve. 8 hours was by auto winding and through a normal day, not banging it right and left. Anyway I have more than 20 hours reserve in other watches I have by just wearing them all day and I would be happy if this had 16 for example. As you said 8 hours is not enough when you sleep only 7-8 hours every night or if you have a shower in the afternoon and forget the watch in the bathroom on a Sunday …, waiting it to be ready Monday morning when you go to work

ChrisN · Apr 28, 2021

If you had 40 hours reserve with manual winding but only 8 hours after wearing all day while being active, then I would look first at the auto system. Even if you didn't give it an initial wind when you picked it up and set the time, no auto system is designed to just build 8 hours reserve in one day. If the spring was set, then the manual wind power reserve would also be low and the explanation you have understood doesn't make sense anyway.

You also seem to be happy with reduced power reserve after auto winding and it should be the same as with manual winding so, if you are regularly seeing this then something is wrong. Obviously, you need to wear the watch for a few days from zero reserve to build up full reserve - always better to wind the watch twenty times when you set the time if it has been out of rotation and has stopped.

Cheers, Chris

loniscup · Apr 28, 2021

Forgive me but, after a service I expect the power reserve to be as close as it can be to the specifications of the movement and not to hope for 16hours so it is ok after a night's sleep.

Dan S · Apr 28, 2021

If the watch has 40 hours power reserve with manual winding, the problem doesn't seem to be mainly with the mainspring.

NGO1 · Apr 28, 2021

Here a 20yo main spring from my recently serviced Monaco.
Just giving this thread a visual.