mainspring searching

[dirkwulf]

very new to the hobby and just starting in on my first few practice movements. this one is a USA wristwatch, Elgin 33154921.  Which I have not found much info on for parts.  My mainspring measurements come up as 1.84mm high, .08mm thick with a 11mm barrel ID and 3.4 arbor OD.   If I try to run a string along the length and measure i come close to 400mm however using calculations I saw online   L=3.14(R^2-r^2)/2t  I get 536.94 .  I have looked on CAS-KER's Us site and on COUSINS UK site and have not been able to figure a GR code or part number close to those measurements.  Any help would be appreciated but am more interested in what I may be doing wrong or directions to get the right answer over just which mainspring is right.

 

[dirkwulf]

took me a min to get some pictures transferred.

[AndyGSi]

Welcome to the forum.

So from the Serial No you can find from the following sites that it's a Grade 485 Movement.

https://www.elginnumbers.com/index.php

https://pocketwatchdatabase.com/search/result/elgin/33154921

If you then look at the attached PDF you'll see it's a 4789 Mainspring.

An eBay search comes up with these as an example but there is a slight conflict on the strength.

https://www.ebay.com/itm/115496722196?norover=1&siteid=1&mkevt=1&mkcid=16&chn=psoc

https://www.ebay.co.uk/itm/374299307774

The Pocket Watch Database site above also confirms this.

Edit

And again a slight difference on the strength.

Final Edit

If you wanted a GR Mainspring then you could check this site which doesn't appear to be working correctly at the moment.

 

Grade 481 to 520.pdf

Edited April 2 by AndyGSi

[JohnR725]

1 hour ago, dirkwulf said:

CAS-KER

If you look carefully on their website they have a nice PDF to download which I will attach. Then you can take your dimensions and figure out which mainspring you're supposed to have. It also give you the various numbers of the mainspring so you can go look on eBay

42 minutes ago, AndyGSi said:

you'll see it's a 4789 Mainspring.

One of the problems with part numbers for American pocket watches will be or can be typically with balance staffs and mainsprings will be size variations for the same part number. Typically with Elgin when they give you a part number they will give you the thickness of the spring.

If you look at the above example I have you'll notice that for some of the Springs for the same part number you did have various thicknesses or strengths. As time has gone on the quantity of mainsprings available especially the aftermarket springs the quantities or the choices of thicknesses will go away. In other words you're lucky sometimes to get a mainspring at all.

Then from a different listing for the particular part number we can see that the blued steel spring originally came in three different thicknesses. With the initials DP standing for Elgin's alloy DuraPower.

Personally especially on the smaller size American watches I would try to go with the original spring as they will be more likely to be sized correctly. Then DuraPower Would be the preferred choice. Then even though the listing up above only shows one thickness/strength according to the seller below there were three different thicknesses and other words you get a choice.

https://www.ebay.com/itm/156090848585

 

Mainsprings Cas-Kar Catalog 2018.pdf

[AndyGSi]

This shows the strength as 0.17 which appears to contradict everything else?

13 minutes ago, JohnR725 said:

[JohnR725]

1 hour ago, AndyGSi said:

This shows the strength as 0.17 which appears to contradict everything else?

I wonder if somebody copied the number wrong? Because that would definitely be stronger than anything else we have listed that would be more like a mainspring for something much much bigger.

Then often times at least in this country the mainsprings you get are Sometimes repackaged GR mainsprings and that would give you a clue if there is a problem but here they have the right thickness so I'm assuming somebody just made a clerical mistake?

4 hours ago, dirkwulf said:

11mm barrel ID and 3.4 arbor OD.

Oh and if this was a standard Swiss spring and you wanted to shove it in from the ring that it comes in having the barrel ID is nice. With a spring like this with the protruding parts that have to go into a slot in the barrel it's extremely unlikely you can just shove it in from the ring. This means you either will have to hand wind the spring in or if you in a mainspring winder which is what I would preferred there is a procedure. But I'm assuming that you probably don't have a mainspring winder so you'll probably put it in by hand but the case are long I will show you the procedure that I like.

Then having the arbor dimension would be really nice if that was a specification but it's not. With the aftermarket not following the original of the American pocket watch. Personally I find it's a much bigger issue with the smaller size watches like this which is why if you get an original spring it would be preferred.