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Discussion Starter · #1 ·
Hi guys, need a quick bit of advice as cannot find any info out there on this...

Will an ETA 2892 mainspring fit into an Omega 1120 movement?

Omega's part, as you may have guessed, is around 6X the price!

Thanks very much!
 

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Yes, theoretically it should.
Notice the mainspring dimensions in the two Ranfft archive entries below:
bidfun-db Archive: Watch Movements: ETA 2892-2
bidfun-db Archive: Watch Movements: Omega 1120 (ETA 2892-2)

Oddly enough, the cal. 1120 appears to have 5 hours of power reserve more than the standard 2892, so while they theoretically share the same mainspring, there must be more to that- I don't pretend to know what exactly causes that difference, though.
Take the information posted on Ranftt with a grain of salt - although it's a great general resource, it has it's limitations.

The ETA 2892A2 has a rated power reserve of 42 hours. The Omega 1120 has a rated power reserve of 44 hours - this is directly from Omega's documentation, so I have no idea where Ranftt gets 47 hours from.

Coincidentally I recently finished a Longines with an ETA 2892 inside, and in my power reserve testing after spending time on the final test winder, it ran for 50 hours - I have had many 1120's run that long and a few even longer. The power reserve indicated by brands will typically be underestimated, so if the movement is in good condition and has been properly serviced, it will run much longer than the rating.

I don't believe you will find that there are any dimensional differences between a 2892 mainspring and an 1120 spring. They are both made by Nivarox, and the only thing I'm not 100% sure of is that they are the same alloy, as I have no way to test that.

Not sure where the OP is getting the Omega spring from, but the prices are pretty much the same for me...

Hope this helps.

Cheers, Al
 

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Take the information posted on Ranftt with a grain of salt - although it's a great general resource, it has it's limitations.

The ETA 2892A2 has a rated power reserve of 42 hours. The Omega 1120 has a rated power reserve of 44 hours - this is directly from Omega's documentation, so I have no idea where Ranftt gets 47 hours from.

Coincidentally I recently finished a Longines with an ETA 2892 inside, and in my power reserve testing after spending time on the final test winder, it ran for 50 hours - I have had many 1120's run that long and a few even longer. The power reserve indicated by brands will typically be underestimated, so if the movement is in good condition and has been properly serviced, it will run much longer than the rating.

I don't believe you will find that there are any dimensional differences between a 2892 mainspring and an 1120 spring. They are both made by Nivarox, and the only thing I'm not 100% sure of is that they are the same alloy, as I have no way to test that.

Not sure where the OP is getting the Omega spring from, but the prices are pretty much the same for me...

Hope this helps.

Cheers, Al
As always, the cavalry has arrived:). Thanks for the clarification, Al. Well, every resource does have its limitations indeed... If I recall correctly, the good Doctor's using manufacturer's tech specs, quite certainly also Bestfit- most of the movements in his archive are ones he has handled himself, but some photos and info come from his acquainted watchmakers and watch collectors. It may well be, that the one he has been checking out has been running for 47h. Or he has made a typo... He's on WUS, posting in the Vintage forum from time to time, so you can ask him if you want.

I've noticed inconsistencies in the archive before- a lot of well-known movements are missing from it (for example, the Zenith 120, the MST 360...), and the production figures tend to be inaccurate sometimes (differences between the figures provided in the archive entries for some Zeniths, and the info in Manfred Rossler's Zenith book).

As I'm spending a lot of time researching the vintage stuff, the Ranfft archive is pretty much a holy scripture to me, and it rarely has ever failed me- guess this one goes to the rather short list of cases, in which it actually did.
 
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Ranftt is a good resource as I said, just that for very specific technical information, I would not trust it. By that I mean that I would cross check the information elsewhere if at all possible, in particular for things like mainspring sizes because I have seen sources that certainly contradict the sizes he has given in a few cases. I know he's on the site...

Cheers, Al
 

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Discussion Starter · #6 ·
Thanks very much for the feedback guys, much appreciated... I buy them from Cousins in UK, ETA spring around £6, Omega version around £35 as I recall. Obviously if the ETA one fits that will by my choice!

I'm not an expert, but I can only guess the longer power reserve of the Omega is due to the barrel pivots sitting in jewels rather than plan sleeves?

Yes, Ive also found that most ETA power reserves are longer than officially stated, at least on fairly new movements anyway.

So, I'll get this spring ordered following your advice.
 

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I'm not an expert, but I can only guess the longer power reserve of the Omega is due to the barrel pivots sitting in jewels rather than plan sleeves?
6 pounds is very cheap for a branded mainspring, so does it come in an ETA package, like this:



As you can see here, it should have the ETA logo on the package:



If not, they could be selling you a generic spring "to fit" an ETA 2892, rather than a genuine ETA part. The terminology used on the description is important to pay attention to. Of course they are charging a premium for the Omega spring as they can't get them anymore. It seems everyone is making as much as they can on the parts they have left after being cut off, and since they were cut off all Swatch product including ETA mainsprings, it doesn't make sense that they would be charging so little for a proper ETA spring as I've shown. If it's a generic spring, then I would personally reconsider using it - the mainspring is the engine of the watch and if it is not delivering a smooth and constant flow of torque to the wheel train, then performance can surely be affected.

Anyway, on the theory above that I quoted, having a jewel or bushing here has no effect on power reserve. The barrel arbor only turns during winding, so any reduced friction at this point is affecting the efficiency of the automatic winding system, rather than how long the watch runs on a full wind. In most modern watches, the barrel turns and the arbor stay stationary as the watch runs down...

Cheers, Al
 

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Discussion Starter · #8 ·
That's awesome info, thanks Al. You might be right about the mainspring, I can't see any mention that's it's an ETA part, although it is listed under the ETA parts category. I'd probably best try and find one elsewhere then, as I quite agreed about it affecting the constant flow and torque to the system.

Good point about the barrel jewels, hadn't really thought about it that much, but make sense now... so in reality the Omega upgrade doesn't really make much difference I guess.

It's a shame about the constant availability problem of ETA parts, indeed... hope one day the situation gets back on track!
 
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