Omega Seamaster 351 and 354 mainspring condition

[Andy F]

Recently I have been working on the above two movements, one for a friend and one my own. Upon opening the barrel and removing the mainspring, I noticed that once the arbor was removed, the arbor end of the mainspring was under such tension that the end that wraps on the arbor sprung itself up against the wound up coils of the mainspring in the barrel. I should have captured photos but didn't think of it at the time. I am used to seeing the arbor end of a mainspring centered within the barrel, not sprung out toward the outer coils of the mainspring. I replaced both mainsprings and the replacements had the arbor end centered. One of the watches (351) has been back together and running well for four weeks. I am not finished yet with the other (354).

What causes the spring to take this "set" upon removal of the arbor? I doubt its normal because of the load this must place on the arbor against the barrel. Is it a sign of a worn mainspring? Were they just "bodged" and I was unlucky enough to have two like that?

Edited: Dec 29, 2020

 

[Archer]

It's not unusual for the arbor end of the spring to not line up with the hole in the barrel. Generally I don't see this as a real problem.

Cheers, Al

 

[Canuck]

A Andy F

Recently I have been working on the above two movements, one for a friend and one my own. Upon opening the barrel and removing the mainspring, I noticed that once the arbor was removed, the arbor end of the mainspring was under such tension that the end that wraps on the arbor sprung itself up against the wound up coils of the mainspring in the barrel. I should have captured photos but didn't think of it at the time. I am used to seeing the arbor end of a mainspring centered within the barrel, not sprung out toward the outer coils of the mainspring. I replaced both mainsprings and the replacements had the arbor end centered. One of the watches (351) has been back together and running well for four weeks. I am not finished yet with the other (354).

What causes the spring to take this "set" upon removal of the arbor? I doubt its normal because of the load this must place on the arbor against the barrel. Is it a sign of a worn mainspring? Were they just "bodged" and I was unlucky enough to have two like that?

This usually happens prior to disassembly when the mainspring power is released too rapidly, allowing the ratchet wheel to over-rotate, causing the arbor to “back out” of the centre coil of the mainspring.

 

[Andy F]

Thanks for the replies so far. In both cases though the arbor was still captive in the center of the mainspring. Only after removing the arbor did the center coil unload itself and rest against the coils of the remainder of the mainspring. You have me thinking though. Is it possible that the way I am letting the spring down is causing the spring to unwind in an "unnatural" way?

 

[Archer]

A Andy F

Thanks for the replies so far. In both cases though the arbor was still captive in the center of the mainspring. Only after removing the arbor did the center coil unload itself and rest against the coils of the remainder of the mainspring. You have me thinking though. Is it possible that the way I am letting the spring down is causing the spring to unwind in an "unnatural" way?

No, even new mainspring will be this way sometimes - here's an example:





Unless you are not controlling the release of power on the mainspring, it's not anything you are doing that causes this.