Solving knocking

[Simeon]

I have just serviced a 1950's(?) Wittnauer 10S (actually seems to be an AS1200 as base calibre). This watch came to me with a broken balance pivot and extremely gummed up. I replaced the balance complete and cleaned and serviced the watch. The old blue mainspring was also set so I replaced it with a slightly stronger 0.01mm I think) GR mainspring as the original size was no longer available.

The watch performs exceedingly well - too well in fact. With DU and DD amplitudes in excess of 310 degrees with a full wind. In vertical positions it does around 270-280 degrees. As you can imagine, it gives a galloping, knocking sound when DU/ DD but only when fully wound. When it had been running for about 20 hours it was a reasonable 270 degrees DU / DD and about 220 degrees in vertical positions with good rates and beat error so there's nothing structurally wrong with it. I obviously have a problem with knocking (or is it called over-banking?).

This article suggests that this is common for old watches with new, white metal mainsprings and suggests a few 'dodgy' solutions to try and prevent / mitigate the knocking. I haven't looked at adjusting the banking pins (they looked vertical to me so wasn't particularly expecting to have to adjust them). Things like running the escapement with minimal lubrication, using a heavier oil on the balance or lubricating the pallet fork pivots.

Which of these solutions would you choose or what would you do differently?

 

https://adjustingvintagewatches.com/amplitude-attacks-dealing-knocking/

 

 

[JohnR725]

5 hours ago, Simeon said:

I haven't looked at adjusting the banking pins

the banking pins are safety feature of the watch adjusting of them for other reasons will probably have other consequences.

5 hours ago, Simeon said:

The old blue mainspring was also set so I replaced it with a slightly stronger 0.01mm I think) GR mainspring as the original size was no longer available.

I don't suppose you remember the mainspring number? Then it would be preferred to replace the mainspring was something slightly lighter rather than modifying the watch to work with your overpowered mainspring. but it would be nice to have the mainspring number so I can know the actual spring to compare what I perceive the watch is supposed to have.

 

[Simeon]

3 hours ago, JohnR725 said:

the banking pins are safety feature of the watch adjusting of them for other reasons will probably have other consequences.

I don't suppose you remember the mainspring number? Then it would be preferred to replace the mainspring was something slightly lighter rather than modifying the watch to work with your overpowered mainspring. but it would be nice to have the mainspring number so I can know the actual spring to compare what I perceive the watch is supposed to have.

 

The mainspring I used was a GR4514 1.60 x .11 x 300 x 9mm. The required mainspring was a GR4486 at 1.60 x 0.100 x 300 x 9.0 mm

[Simeon]

Here's the old mainspring. Not kinked or coned shaped but had been sitting fully wound for a long time. 

[JohnR725]

for an alternative number you go to eBay and search for this mainspring 711K.

then you may find the numbers a bit confusing because they typically and Dennison numbers not metric so I've attached a conversion chart. In any case you get a mainspring for between 10 and $20

Mainspring - DennisonChart.pdf

[Klassiker]

Why not refit the old mainspring first? Maybe it isn't set after all.

[Simeon]

20 minutes ago, Klassiker said:

Why not refit the old mainspring first? Maybe it isn't set after all.

I may well. I will probably have to wait a few weeks for a delivery, so I might as well try the original in there. If nothing else it will be an experiment in how much contribution a new mainspring makes compared to an old one. 

30 minutes ago, JohnR725 said:

for an alternative number you go to eBay and search for this mainspring 711K.

then you may find the numbers a bit confusing because they typically and Dennison numbers not metric so I've attached a conversion chart. In any case you get a mainspring for between 10 and $20

Mainspring - DennisonChart.pdf 41.23 kB · 0 downloads

Thank you, I had a look at Dennison sizes and the 711K but got put off by measurements in inches (plus Ofrei won't post overseas). I rhen found the overly strong GR spring at Cousins instead (because I thought it was an easy option). I will have to hit eBay armed with this additional search term!

[AndyGSi]

You could look at just getting a GR4484 or GR4485 from Cousins which are just shorter versions of your GR4486.

[Neverenoughwatches]

1 hour ago, Klassiker said:

Why not refit the old mainspring first? Maybe it isn't set after all.

Doesn't look too bad to me either, I've re- fitted much more set springs than this and they still run with adequate amplitude but run a little short on reserve. Throwing in a new stronger mainspring isn't the answer to overcoming excessive friction, i woukd check everything else was functioning  well first, a new spring woud be my last resort.

1 hour ago, Simeon said:

I rhen found the overly strong GR spring at Cousins instead (because I thought it was an easy option). 

Dont do it !!! , get the most you can from the spring you have.....fitting an overly strong spring as you describe it.....doing this may cause REBANKING....not again I'm fed up of hearing this word ....or you may end up pushing through excessive friction in the train to get what you want.......thats going to create more torque in the train up to the point of where the friction is.......which could  very well be starting at the barrel end.....solve any friction first through the testing of function groups.....then when everything else checks out ok and you have good free running..look at changing the spring, at that point you probably wont need to. 

[nickelsilver]

1 hour ago, Simeon said:

I may well. I will probably have to wait a few weeks for a delivery, so I might as well try the original in there. If nothing else it will be an experiment in how much contribution a new mainspring makes compared to an old one. 

 

It's not so much old vs new, as weaker vs stronger. A 0.01mm increase on a 0.10mm thick spring is significant.

 

I have worked on many older, vintage, antique watches- for the factory. In most cases they wanted me to reuse the mainspring. I have compared new to old many times though, same dimensions, including steel to modern alloy, and most of the time the results were close enough to be considered identical. This is true also for steel springs that most would consider "set"- if it opens up to at least the movement diameter, it's really fine.

 

I know there's a push to always replace the mainspring, but there's a good argument for keeping the old/original one: the fact that it has lasted for years (perhaps decades) proves it's reliable. I have dealt with far more broken mainsprings post-repair where it was a new one I installed than repairs where I reused the original. I'm quite sure this is the thinking from the Factory I did work for; in many cases the cost of the repair was well over 1k, so 10-20 bucks for a spring is nothing in the mix.

[Neverenoughwatches]

8 minutes ago, nickelsilver said:

It's not so much old vs new, as weaker vs stronger. A 0.01mm increase on a 0.10mm thick spring is significant.

 

I have worked on many older, vintage, antique watches- for the factory. In most cases they wanted me to reuse the mainspring. I have compared new to old many times though, same dimensions, including steel to modern alloy, and most of the time the results were close enough to be considered identical. This is true also for steel springs that most would consider "set"- if it opens up to at least the movement diameter, it's really fine.

 

I know there's a push to always replace the mainspring, but there's a good argument for keeping the old/original one: the fact that it has lasted for years (perhaps decades) proves it's reliable. I have dealt with far more broken mainsprings post-repair where it was a new one I installed than repairs where I reused the original. I'm quite sure this is the thinking from the Factory I did work for; in many cases the cost of the repair was well over 1k, so 10-20 bucks for a spring is nothing in the mix.

I realised this and came to the same conclusion earlier this year,( all by myself may i add )  swapped a stronger spring for the original one that i was convinced was set ( looked worse than the OPs ) in a little old Oris. The stronger spring caused high amplitude and rebanking, easy to hear in the mic and the tg trace and readings showed a regular step in the rate happening. Despite the high amplitude it still had low power reserve. Decided to go back inside and see if i could find some friction somewhere, found it in an incorrect cannon pinion fitted, rubbing on the plate, solve this then re-fiited the original spring.  Touted power reserve is about 40 hours, this is getting 35ish now .

Amplitude is 260ish after an hour of full wind, then down to 210ish after 24hrs. This could be from the original factory spring.

[Simeon]

1 hour ago, Neverenoughwatches said:

Throwing in a new stronger mainspring isn't the answer to overcoming excessive friction, i woukd check everything else was functioning  well first, a new spring woud be my last resort.

That wasn't why I did it. The train was running free with limited friction after service.i was not trying to overcome any deficiency in the train with a stronger mainspring. 

I did it because I thought that the mainspring was probably done for after sitting fully wound for decades and also not wanting to have to wind the mainspring back into the barrel with my Chinese mainspring winders (or more likely by hand since the winders are only suitable for maybe 1 in 4 mainsprings). Swapping out the mainspring seemed better practice than messing around with an ancient mainspring, unfortunately I chose the wrong one. 

[Neverenoughwatches]

1 hour ago, Simeon said:

That wasn't why I did it. The train was running free with limited friction after service.i was not trying to overcome any deficiency in the train with a stronger mainspring. 

I did it because I thought that the mainspring was probably done for after sitting fully wound for decades and also not wanting to have to wind the mainspring back into the barrel with my Chinese mainspring winders (or more likely by hand since the winders are only suitable for maybe 1 in 4 mainsprings). Swapping out the mainspring seemed better practice than messing around with an ancient mainspring, unfortunately I chose the wrong one. 

Makes sense Simeon to avoid future issues and work, as already discussed a new mainspring just isn't a necessity if the current one can do thd job. I wasn't particularly aiming my comments to your situation decision making....so no offence intended as to your reasoning. More with me about providing information that i feel is relevant so that other new learning folk can pick up and think about. 

[Simeon]

Just to loop back to this. I got back from a week's holiday and got back around to reinstalling the old mainspring. Comparison with the new but stronger spring shows that the old spring was quite set considering that they are supposed to be the same length. A full wind and onto the timegrapher - 200 degrees amplitude. Definitely no knocking!

Thanks for the tip about Dennison sizing @JohnR725. I have ordered a new white alloy spring in the 711K size.