Mainspring sizing and sourcing

[nickvon]

Hello all,

I am a complete novice working on my first movement. I have successfully (as in I didn't lose anything) taken apart, cleaned, greased/oiled and reassembled an ETA 2375. I bought myself a time-grapher and have managed +/- 0 s/d, 230 degrees amplitude and a woeful 2.4ms beat error. Not bad considering I had to disassemble the entire balance to attempt to oil it as it has no incabloc. Anyway, ignoring the beat error, the amplitude I think is a touch low, and I suspect that's because I cannot put more than 10 winds into the main spring until I feel something (I assume the mainspring) slip. So far as I can tell, the mainspring for this movement has the following dimensions 1.5(h) x 0.11 x 374(l) x 10.5 (barrel). I searched Cousins Uk which I understand to be the main repository for mainsprings, and I cannot find any automatic mainsprings with a bridle termination in this size, or anything that close. I did more searching and found this very helpful website  https://www.timeparts.nl/ and after sending them an email was advised that I needed to order a 1.5x0.11x380 which they had in stock, but it didn't have a bridle like the original one, but rather one that simply terminated. I suspect therefore that it's not putting enough pressure on the barrel wall to prevent slippage.

So to cut a long story short, I assume there are only two parameters that allow some kind of flexibility in terms of finding the closest correct mainspring for a barrel, thickness and length, is this a correct assumption, and if so how much flexibility does one have? The second question is, where can one shop for mainsprings, other than Cousins and https://www.timeparts.nl/ that I might be able to find my correct part?

 

Edited October 26, 2024 by nickvon

[RichardHarris123]

Strength (thickness) and height are the most important factors.  Length changes the reserve, the amplitude may or may not be related to the mainspring. 

[AndyGSi]

So you didn't find this on Cousins looking under parts for the ETA 2375.

As @RichardHarris123 said, the amplitude may or may not be related to the mainspring.

Depending where you are in the world there are numerous places for parts in general.

https://www.watchmaterial.com/eta-2375-2381-2384-automatic-mainspring-self-lubricating/

Edit

What bridle did the original have? Was it a separate one?

What was it you actually got from timeparts?

 

Edited October 26, 2024 by AndyGSi

[JohnR725]

8 hours ago, nickvon said:

because I cannot put more than 10 winds into the main spring until I feel something (I assume the mainspring) slip.

it's probably not broken and yes it's supposed to slip sort of?

8 hours ago, nickvon said:

but it didn't have a bridle like the original one, but rather one that simply terminated. I suspect therefore that it's not putting enough pressure on the barrel wall to prevent slippage.

it would really be nice to have pictures so we can see what the end of the mainspring looks like.. Then did you apply breaking grease to the outer barrel wall?

 

[nickvon]

It would of course have helped if I looked in the right place! Thank you AndyGSI, I was looking under the unbranded section, I didn't think to look for the brand of the movement itself! 

I actually live in Switzerland, and I have yet to find an online supplier of watch parts here.

John, I shall post an image of the spring later in the week when I have a chance to take out the barrel. I have indeed put breaking grease on the outside of the barrel, Mobius 8213.

This will be the third attempt at getting a mainspring in, the first was for a bigger 11mm barrel because I measured badly, so that ended up springing across the room, and the second I shall post on here to get your opinion on the termination. In the meantime I shall order the correct mainspring from Cousins.

Is there a technique to getting a mainspring in without a winder? Both time have been failures with the spring unravelling. It seems the termination end of the spring that pushes against the barrel wall tends to not slide in and fouls on the edge of the barrel. Should one angle this part in first, and then work the rest of the spring in?

 

[AndyGSi]

Note that the GR4154X is also designed for an 11mm barrel so without a winder your only option would be to wind it in by hand.

What part number was the mainspring you've already got and what's currently in the barrel as it does appear to have a bridle?

[JohnR725]

6 hours ago, nickvon said:

I actually live in Switzerland, and I have yet to find an online supplier of watch parts here.

before online material houses there were physical material houses existed in the real world. Scattered across the planet including possibly Switzerland? So depending upon the city lived in there may have been one or more material houses you could physically go there. Stand at the counter asked for your parts and they would bring you the parts. If you weren't in the big city you could telephone or fax or even just send a list by mail. In some of the old catalogs and stuff I've acquired I've seen the forms you could fill out for ordering parts.

The only reason I bring up these physical material houses are some of them still exist and are still not online. Another is the minor little problem of some of them won't sell to people unless you have a business license it depends upon probably where you are on the planet. Some of it has to do with tax reasons.

The reason I bring this up it seems very hard to believe that the risen to material house somewhere in Switzerland?

6 hours ago, nickvon said:

Is there a technique to getting a mainspring in without a winder? Both time have been failures with the spring unravelling. It seems the termination end of the spring that pushes against the barrel wall tends to not slide in and fouls on the edge of the barrel. Should one angle this part in first, and then work the rest of the spring in?

usually the most common thing people do is push it out of the ring directly into the barrel. You do need to make sure we are pushing that you push the entire spring and not push the middle first. This is because most people don't have a Winder and don't want to deal with winding mainsprings.

The most likely place for you would have a problem but not on this watch would be some barrel set have protruding  hook to catch the mainspring and that presents a problem when inserting not to catch on that.

On 10/26/2024 at 11:51 AM, AndyGSi said:

this on Cousins looking under parts for the ETA 2375

just to make sure I looked in the parts catalog and we get the same part number for the mainspring