Mainspring condition

[Klassiker]

Is there any way to spot a tired mainspring without removing the spring from the barrel? Are there any visual clues, or tests, that indicate with reasonable certainty that the spring needs replacing, or that it is in good condition and can be re-used?

Edited April 26, 2020 by Klassiker

[vinn3]

no,     there could be rust penitration where you cant see.    book and videos  will show you how to properly do it.   ITS well worth it.      good luck,   vin

[rodabod]

Most likely sign would be if it’s an older blue steel type. 

[Nucejoe]

You can make a torque o meter of your own, solder a ratchet screw to a bar( hand) and some weights to hang on the bar. Surely there are proprietory tools made for manufacutrers, based on the same principle. Your watch is best tool itself, wind and make a record of how long it runs, to have a better graph repeat at half wind and fourth so on to get a graph of primery coils strength and thereon , in addition to power reserve you theoretically want a smooth curve for the torque throughout the length of mainspring. You agree why just replacing with a new one is the easiest and cheapest.

[Klassiker]

I was thinking more along the lines of how tight the coils lie against one another in the relaxed state. Looking at this example:

 

It takes the spring over one-and-a-half turns from leaving the arbor to resting against the inside of the outer coils. I've seen lots of other examples where the same thing happens in a half to three-quarters of a turn. Is that significant at all?

This watch does have very low amplitude, in fact it hardly runs at all, but that could be down to any number of things. Would anyone suspect a tired mainspring, just going on its appearance?

Edited April 28, 2020 by Klassiker
Wrong photo

[Nucejoe]

I'd test the mainspring for strength, by manual supplement of torque to the barrel.

[rodabod]

20 hours ago, Klassiker said:

I was thinking more along the lines of how tight the coils lie against one another in the relaxed state. Looking at this example:

 

It takes the spring over one-and-a-half turns from leaving the arbor to resting against the inside of the outer coils. I've seen lots of other examples where the same thing happens in a half to three-quarters of a turn. Is that significant at all?

This watch does have very low amplitude, in fact it hardly runs at all, but that could be down to any number of things. Would anyone suspect a tired mainspring, just going on its appearance?

I don’t think that’s a fair way to assess a spring as it may be annealed towards the end to aid the hole punch and forming of the section which holds against the arbor. Plus there are other variables such as the strength of the spring. 
 

In my experience, white alloy springs do not tend to lose much of their power storage. Sometimes I’ll gain ten degrees of amplitude when swapping old for new, for example. For this reason, I do not always swap out springs. That’s down to personal opinion. I’ll almost always bin it if it’s blue steel.

 

[nickelsilver]

In my experience power problems are almost never due to a fatigued mainspring. This includes steel springs. There is certainly no way to assess a spring that is in its barrel; with steel springs the old rule of thumb is that it expands to about 3x barrel diameter when removed. With alloy springs, depending on the type, they will expand further and for most have the "reversed S curve" towards the outer hook.

 

I do a fair bit of work for one of the older and bigger Swiss high end companies, on their vintage pieces (like 1960s and older). These often have quite hard to find mainsprings, either because their height is very low, or special T ends, or whatever. The standard practice, from them, is to not change the spring. Exceptions would be a spring that had been changed in the past and is obviously wrong; usually a thicker spring to compensate other problems, with a shortened running reserve as a result, or a spring that is damaged i.e. kinked or showing signs of cracking at the hooking points. In several years of doing these I think only one has come back- it it did have its spring changed for a new GR at the time of service.

 

That's not to say that it's silly to change the spring when servicing- for modern pieces with ready replacements it's good practice. Just want to point out that the mainspring is really rarely the reason a watch (or clock) is running poorly. In the above example of a watch having an oversize spring installed, typically I find that the escapement is poorly adjusted, pivots might have wear, unjeweled holes in the plate (barrel, center wheel) are worn, the barrel itself is worn and sloppy on its arbor, etc.