ETA 12836 runs very well after service, but with extremely low amplitude

[cortman]

Hi all,

As the subject states, I'm having an odd problem with an ETA 12836 movement I just serviced. It runs steadily with an excellent trace on the timegraph, but with very low amplitude (175-190). It also doesn't appear to usually start running when the watch is wound; it takes a little shake or nudge of the balance wheel to get it going, but once it's going it runs consistently and smoothly.

I have disassembled the entire wheel train and re-cleaned them to be sure I didn't over-oil. I checked that the mainspring barrel was seated correctly. I removed the top balance jewels, soaked the entire balance in one-dip and reassembled with a fresh drop of oil, and the watch shows absolutely no improvement. I have also tried demagnetizing to no effect.

The movement and wheel train all seem to be in great shape as is the balance. When given a puff with an air blower the balance oscillates very freely, continuing to move down to a very small increment.

In the course of the service I replaced the mainspring with a brand new one from a reputable (I think?) dealer (watchmaterial.com). I greased the barrel wall in six places with 8217 before installing the mainspring.

I am really at a loss as to why the amplitude is so low. Is there something I'm overlooking here?

Thanks a lot!

EDIT: I should add that visually the balance runs true and snappy, but it does appear to have a very short arc.

Edited January 14, 2023 by cortman

[dadistic]

A movement requiring a shake to start is an indication that the watch is very far out of beat.  Your timegrapher may not be giving you good information. 

[cortman]

18 minutes ago, dadistic said:

A movement requiring a shake to start is an indication that the watch is very far out of beat.  Your timegrapher may not be giving you good information. 

Oh that's a very good point that I hadn't even thought of. Makes a lot of sense. I'm going to play with that a bit and report back.

[HectorLooi]

2 hours ago, dadistic said:

A movement requiring a shake to start is an indication that the watch is very far out of beat.  Your timegrapher may not be giving you good information. 

But looking at his timegrapher trace, his beat error is zero. Could be a dirty balance of pallet fork.

[ColdWind]

I assume that you did check the wheel train and balance wheel, so that they're all good, the train runs with almost no friction and the balance oscillates very freely. Timgrapher shows stable running means the escapement is ok. At this point I think the problem could be some where in the mainspring barrel. I once had a case that the watch runs at low amplitude because a previous watchmaker damaged the barrel lid putting it back in using tweezer. Basically the lid got bent inward and it was rubbing against the mainspring. I bent the lid back to flat and that solved the amplitude problem. You did replace the mainspring with a new one from a reputable dealer so the mainspring height should be right, but check for that as well.

[fellerts]

How does the balance spin if you remove the escape wheel and give the balance a puff of air? The balance should be able to move the pallet fork from side to side without much resistance. However if the impulse jewel or the pallet fork horn is dirty you could lose a lot of amplitude there. I had an ETA 2472 with very low amplitude that was solved by properly cleaning the horn.

[Nucejoe]

Does adding little power ( manually) to the barrel , give you GOOD  the amplitude?   If not lets see the lock of pallet on escape teeth. 

Regs

 

[cortman]

Just closing the loop on this one- the mainspring slipped off the arbor, and in the process of re-shaping it to catch it broke- so I got an entirely new mainspring/arbor/barrel assembly (only a couple dollars more than just a mainspring, surprisingly) and after installation and reassembly, I'm getting 290 degrees right away. It appears the mainspring was probably not correct for this watch (boo, watchmaterial!).