Eta 2783 Mainspring

[canwdarose]

Guys - tonight I broke the arbor end (with the hole) of my ETA 2783 mainspring where it grips the lug on the arbor - those moments are the reason swear words were invented.  ham-handedness isn't normal, but tonight a momentary lapse of judgment and that was that.

 

I have the specs for the spring - 1.45mm height, 0.12mm thickness, 368mm length, 10.5mm barrel diameter, and as I said it has a hole end (actually slotted hole) and the 2783 is an automatic movement.

 

Any suggestion on sourcing a replacement?  I had a quick look at Cousins and Ofrei, but the GR3729 is obsolete on Cousins and Ofrei only had a couple options that were close but not exact.  And neither defines the end type - or at least my knowledge of horological parts is not up to scratch.

 

Can someone point me to the correct way to assess potential equivalents or substitutes and order a replacement?  I can make some guesses about whether a 1.4 height or 0.11 thickness or 360 length spring will or will not work, but I really want to know how to assure I get the correct arbor end - a slotted hole is essential for the tiny ramp-shaped lug on the arbor, and I'm assuming one needs the little spot-welded counter-spring on the barrel wall for the automatic to slip at full wind.

 

I can always default to a donor watch on ebay, but looking for options on an actual replacement before I do that.  And I'm up for a repair, but the spring was oddly mis-shapen when it came out of the barrel - didn't have that distinctive "S" shape - was tightly curled - so maybe it's shot anyway - so I'd prefer a replacement

 

Thanks

Bill

[JohnR725]

So I looked up your watch got the numbers below. Then out of curiosity I looked up your spring in my catalog it's definitely not for this watch which is probably why it's discontinued. Then yes you can get the mainspring from cousins image attached.

 

 A/7292
 MAINSPRING 1.45-.125-400 11
 GR 4006-X

[canwdarose]

Thanks JohnR for finding that - follow-on question, though.  How do you know the GR4006X will have the "TR=with Hole" option that is listed?  I would have expected the part number to be GR4006TR, or some such indicator of the end fitting.  Any knowledge you'd care to impart would be appreciated!

Thanks again for the part number.

Bill

[Marc]

 I think you will find that the "DB", "DBH", "T", and "TR" designations refer specifically to the outer end of the spring where it interacts with the barrel, and not to the inner end that hooks onto the arbor.

I am fairly certain that the inner end of the spring universally has a hole to latch onto the hook of the arbor, making it unnecessary to specify this when ordering.

[clockboy]

The X = for automatic & looking it up in my General resorts catalogue the spring ( ETA 2783) quoted by John is correct i.e. GR4006X

 

Why it does not also have TR (with hole) is because it is not a hole end spring but an automatic spring.

[canwdarose]

Aha!  Got it - thanks John, Marc and Clockboy - the fancy ends depicted are interacting with the barrel, not the arbor - didn't realize that before.  Although with the clarity of hindsight, how could those attached bridle pieces have been formed into the tight curl for an arbor connection and withstood the repetitive bending stresses at each winding.  Should have figured that out on my own.  Continuing down that line, those mechanical connections must mean it is possible to over-wind a manual watch?  Or that there is a clutch mechanism to protect the works from an enthusiastic user?  More to discover, I suppose.

 

All the watches I've done so far have been automatics, so now I'm keen to open up one of my "future project" watches that is a manual and see what that mainspring looks like at the barrel end.

 

Thanks again.

[JohnR725]

I've attached some images which may be helpful. So one of the pictures shows the inside that's almost never discussed. I did see one American pocket watch where it required a slightly bigger slots but otherwise I don't even think there's a reference anywhere to the slot size internally. Then a picture of an automatic mainspring laid on the bench.

 

Then regarding ends usually on the packages if it's the standard, normal or tongue end Basically the normal one it's not even mentioned it's just assumed. All the other ones that are mentioned, are mentioned because they're not normal. Basically everything else is for an older style watch. Or if you learned with American pocket watches you always pay attention to the end because they're all different for the various watch companies. Then not shown here there is another variation for the automatic where the last little bit was actually a separate component. Before they permanently attached and made it one spring. So then for that watch it's two separate components or one spring if you can find one that fits which would be better.

[canwdarose]

Great reference images, John - thanks.  I see in the "Yellow Section" image there's the reference to the "X" suffix - meaning "with welded brake-spring...etc" that Clockboy previously pointed out, above.

 

When I pulled the mainspring, it did NOT have the characteristic reverse "S" shape - the barrel/bridle end was tightly curled on itself, just like the arbor end.  I wonder if a previous service wound the spring in backward, discovered their mistake and rewound it correctly, but damaged the spring?

 

Regardless, my foolishness consisted of trying to tighten the grip on the arbor - when I had cleaned and lubed the spring and re-wound it into the barrel, the spring diameter was too large and loose-ish on the arbor, so the lug (which under inspection looks okay) didn't seem to want to engage the hole.  My previous experience (with Seikos, not an ETA til this one) is the arbor is REALLY snug, you need an angled twisting/pushing motion to even insert the arbor into the center of the spring and there is a noticeable 'click' when everything goes home.  Anyway, a little enthusiasm with some needle-nose pliers to tighten the grip and the tip of the spring broke.  

 

I'm getting the replacement on order today... 

 

Thanks again

Bill