Galloping Felsa 100...?

[bsoderling]

Hi guys,

 

I’m working on an old movement in the Felsa 100 series. Main problem was a broken mainspring so I got that replaced and after a cleaning the thing runs strong with an amplitude > 310 and nice straight lines with low beat eror on my timegrapher app.

 

I actually haven’t seen any of my other watches of similar design and age run this well.

 

But....the thing runs crazy about 2 shorter periods per minute as can be seeen in the timegrapher plot.

 

I decided to record and listen to the tick sound and it’s pretty clear; during these periods the tick sounds more like a horse galopping rather than the steady stroll I hear in between.

 

I presume something is going wrong in the interaction between balance jewel, pallet for and escapement wheel and would appreciate any ideas on the cause and what to do about it.

 

 

 

 

 

 

Sent from my iPad using Tapatalk

[rodabod]

It’s knocking the bankings due to excess amplitude. 

[bsoderling]

Hi Rodabod and thanks for the quick reply.

Can you (or someone else) expand a bit on that for an amateur? Or a link to some write-up?

I was kind of having a feeling that the high amplitude could be part of the problem but as I usually hear that one should strive for a 300 degree amplitude (which I usually never get to) I never took that feeling further.

What can be done to reduce amplitude? I usually face the oppsite issue so this a new one for me.




Sent from my iPad using Tapatalk

[nickelsilver]

The new mainspring may be slightly too strong. You can try a slightly thinner one. Either that or you have to get into the escapement, increasing the lock (either by opening the bankings or pulling the pallet stones out a bit or both).

[bsoderling]

Googled a bit and found this:

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

Well explained and interesting.

The author is even using my ”galopping” to describe what the sound resembles [emoji3].

Have to think a bit about next steps but generally very hesitant to fiddle with banking pins and/or pallet jewels.


Sent from my iPhone using Tapatalk

[rodabod]

I have heard in the past that modern balance end-stone and pallet stone lubricants can increase amplitude on some older movements to higher than expected. Some calibers are more prone to this than others. I tend to find that with early IWC Cal 83 movements that I’ll be hitting 310 degrees+ with an original blue mainspring. 

Your best option is probably to choose a thinner spring as nickelsilver suggests. Remember that strength compared to thickness follows a cube law. It’s hard to calculate how much thinner your new spring should be, but as a ballpark figure, maybe try something with 80% or 90% of the thickness of the original. 

270 degrees+ is a good point to aim for as at this point you achieve some level of isochronism as far as balance poise is concerned, ie. poor poise will be less noticeable at this amplitude since the uneven distribution of balance wheel weight will be spread around evenly as it rotates. It’s more of a problem at very low amplitudes (say less than 180 degrees). 

[bsoderling]

I have a feeling that the knocking started after I had added lubrication (9010) to the pallet stones (I tend to forget this during the assembly and have to fiddle with it later on [emoji1]).

I think I will start with removing that oil and continue with the mainspring if it doesn’t help.

I also note that the knocking goes away when the mainspring is somewhat unloaded and delivers less force. So maybe it doesn’t take too much to get rid of it over the entire winding span....




Sent from my iPhone using Tapatalk

[JohnR725]

what you're experiencing is called Rebanking and I have a video below that shows what's going on. The usual causes for this is too strong of a mainspring or if you polish the balance pivots and made them nice and round. The ends a balance pivots are supposed to be not around slightly flat as you actually want a little bit of friction there.

when you changed the mainspring did you get the proper spring for this watch? then mainsprings the blue Springs for the same thickness as a light spring isn't as strong. So if you try a modern spring at the exact size are supposed to have its too strong.

Removing the lubrication from the end of the pallet stones is not considered the proper fix for this. You're supposed to have lubrication on the escapement. If it's borderline wait a couple of days and see if it settled down by itself. I had an instructor in school that said to do that and on some of the borderline ones that solves the problem. then finding a slightly weaker mainspring would be the easiest fix.

https://www.youtube.com/watch?v=Rcqrb3_vin8&t=3s

 

[bsoderling]

Hi and thanks a lot, that video tells it all!

The mainspring is the specified size for the movement. But as it has been pointed out previously it seems that modern materials may have a great influence and the original spec’s is becoming more of a guidance to work from.

I did clean out the pallet fork and escapement wheel from any oil and this did reduce the problem significantly and to only show up for the last few turns on the crown.

This is (as all my watches) not a valuable piece and I will be happy if it runs decently without the desired lubrication.

I will pick up on your advice and let it run for a few days to see if it cools down a bit.

Maybe it’s a bit like an old friend said about issues with his old SAAB (the now gone Swedish car brand); I never touch it, it usually mends itself over time.... :-)




Sent from my iPad using Tapatalk

[bsoderling]

And btw, this is what it looks like put together...




Sent from my iPad using Tapatalk

[nickelsilver]

If the rebanking is just on the very last turns of wind, and probably with the movement perfectly flat, in use on the wrist you'll be fine. If it's for a customer dig deeper. Personal watch wear it and see how it goes.