Slipping automatic mainspring

[fixermole]

I have a NEW automatic mainspring that is prematurely slipping. What to do next?

I installed a new mainspring into a new barrel (the old barrel wall was gouged out bad) and the power reserve only lasted 6-8 h after a full wind. When I wind the crown only 10 or so turns, I can hear the mainspring slip prematurely. The wall of the new barrel is smooth and had 8217 grease applied prior to insertion of the mainspring. Below are pictures of the sourced and installed mainspring; it is in an old Bulova with a 10 CSC movement. Does anything look incorrect or goofy?

I've seen a couple of posts where some suggestions were to rough up the smooth walls or bend out the bridle a little more. Any suggestions or best practices would be appreciated.

 

[mikepilk]

Possible that the bridle hasn't been hardened properly. I fitted a new mainspring which turned out not to be hardened correctly - you could just bend it to any shape.

Maybe take the spring out and check the bridle ?

[Nucejoe]

   Look for sign of slippage on greaesd barrel wall, slippage can happen at arbour too, arbour hook might slip out of MS eye.

 

[steve1811uk]

Shouldn't the bridle be longer, around the length of the barrel wall? Looks to be about 1/6 of a turn maximum. Possibly a faulty part.

[nickelsilver]

That's a normal, non-automatic, tongue end spring. Totally normal that it slips prematurely, it's the completely wrong part.

Edited June 13, 2021 by nickelsilver

[JohnR725]

5 hours ago, nickelsilver said:

That's a normal, non-automatic, tongue end spring. Totally normal that it slips prematurely, it's the completely wrong part.

there is a tiny possibility that this is the correct spring if? In the earlier days of automatic watches the bridal would be a separate component and then a normal mainspring would go in. today all the modern replacement mainspring should come as one component.

 

On 6/6/2021 at 10:25 AM, fixermole said:

old Bulova with a 10 CSC

then something interesting in the Generale Ressorts mainspring catalog it doesn't indicate that this is an automatic mainspring? I snipped out a section higher up on the list there is an automatic and it does say it's an automatic and in the mainspring would have a X on the part number to indicate that is not your regular mainspring which yours does not have?

[fixermole]

Thanks for everyone's input. I thought I was losing my mind. I had originally sent a question on 6/3 asking about the bridle length and got no responses, so I thought it may be OK.

11 hours ago, nickelsilver said:

That's a normal, non-automatic, tongue end spring. Totally normal that it slips prematurely, it's the completely wrong part.

I'm starting to be convinced that what's packed into these Buloloy packs is a manual mainspring with a tongue end as nickelsilver notes. The original mainspring was broken (first picture below) and looked original but I didn't notice the bridle length and chunked it (I know, I know; never throw anything away, right?). The second picture below is the first replacement Buloloy mainspring I installed which obviously slipped like crazy so I removed it and sent the seller a note that they had sold me a manual one, so they shipped another they had in stock. The second Buloloy is shown installed in the original post. I have a third Buloloy pack and the bridle is the same length (4 mm) as the first replacement one I removed.

Any ideas what to do now? I took a quick look around and don't see any online or in the catalogs that are close to the right size going just by measurements. Using the 10CSC model number brings up only Buloloy packs.

JohnR, thanks for the info. I didn't quite follow the text -- do you think there may be a solution out there, or a different part number?

[Nucejoe]

Early type automatic mainspring John talks about.

https://watchguy.co.uk/wp-content/uploads/2012/12/Repairing-Omega-self-winding-watches-bumper.pdf

 

[Nucejoe]

 

[fixermole]

Nucejoe, thanks for the pdf reference and the photo; both are very helpful. More research and hunting to ensue...

[mikepilk]

 

GR3930X is pretty close, just a bit stronger - 1.45 x .085 x 240 x 7.5 Automatic

[fixermole]

Mike, thanks; somehow I missed that when I searched the Cousins site.

Can someone check my math: it appears going from a 0.080 to 0.085 increases the strength by 20%. Is that correct? If so, that seems in the realm of acceptable overpowering, but I'd appreciate input on whether that is too much and will cause undue damage.

Cheers.

[mikepilk]

It is 20% stronger, but the difference is only 0.005 in thickness. How precise will the actual thickness be?   I've measured springs which vary quite a bit along the length, certainly by +/-0.01. 

[JohnR725]

2 hours ago, fixermole said:

Can someone check my math: it appears going from a 0.080 to 0.085 increases the strength by 20%.

this assumes that strength follows a linear curve unless the math takes this into account.

15 minutes ago, mikepilk said:

It is 20% stronger, but the difference is only 0.005 in thickness. How precise will the actual thickness be? 

II don't think I've ever seen published but does anyone know what the percentage of strength variation is with mainsprings?

then we get the interesting thing which is? Omega has a technical document if you have too much amplitude you do use heavier oil uncertain pivots. If that doesn't work you to replace the entire mainspring barrel with mainspring. This would suggest that perhaps Omega thinks that there were variations between the strengths of their barrels? The Elgin watch company when they're doing their final testing if there was too much amplitude the watch would go back to the mainspring department and they would swap with a barrel of lighter strength. In both examples it indicates that there may be a variation in mainspring strength.

So the real life the mathematical calculation is not an exact science at least that's my guess. Then depending upon where the mainspring came from who made it when I was made etc. there will be variations in the strength.

[fixermole]

On 6/19/2021 at 5:51 PM, JohnR725 said:

this assumes that strength follows a linear curve unless the math takes this into account.

John, the 20% is a back-of-the-envelope calculation where thickness has a power of 3 effect on strength, not a linear relationship. I can't find the reference to that right now; it just stuck in my head, thus the request for someone to check it.

[JohnR725]

1 hour ago, fixermole said:

John, the 20% is a back-of-the-envelope calculation where thickness has a power of 3 effect on strength, not a linear relationship. I can't find the reference to that right now; it just stuck in my head, thus the request for someone to check it.

I'm not criticizing your math skills or even the theory other than I don't think it's an exact science I think there's too many variables. Which means at some point in time you just stuck shoving a mainspring in and seeing what happens.

[mikepilk]

8 hours ago, fixermole said:

John, the 20% is a back-of-the-envelope calculation where thickness has a power of 3 effect on strength, not a linear relationship. I can't find the reference to that right now; it just stuck in my head, thus the request for someone to check it.

It comes from the second moment of area for a rectangle = bd³/12

The spring is assumed to be a series of connected rectangles, each acting as a beam in bending.