Mainspring - Re-Use or Replace?

JimInOz · Mar 22, 2019

I have started disassembly of an Omega Caliber 38.5 L T1 (160 family) for @verithingeoff and I'm not sure about the condition of the mainspring. It's not rusted or deformed, but I don't know how set it is so I'm calling for some expert guidance.
(@Archer @ChrisN @Canuck).

This pic shows the fitted mainspring with its protective pools of oil 😉.

This is the free spring, the yellow circle is the diameter of the barrel cap.

So is it still good enough to use or fit a new one?

Ed: I don't know if this is the shape of an Omega spring or if it should be the long "S" shape

JimInOz · Mar 22, 2019

And while the mentors are here..........

I have a stubborn crown wheel screw. I shaped a 300 blade to fit and tried to unscrew it (clockwise) but it wouldn't budge and the 300 screwdriver applies a good amount of force.

I'm reluctant to get too heavy with it in case somebody stronger than me has tried to "undo" it previously.

Any tips on penetrants? heating/freezing? ultrasonic? big hammer?

verithingeoff · Mar 22, 2019

JimInOz
And while the mentors are here..........

I have a stubborn crown wheel screw. big hammer?
Noooooooooooo😲😎

jimmyd13 · Mar 22, 2019

JimInOz
And while the mentors are here..........

I have a stubborn crown wheel screw.

As an engineer, apply gentle heat:

(Of course, Al or others will be along shortly with good advice. Personally, I'd drop it in the cleaner first and try again. Failing that, a quick flash freeze of the screw itself to see if that will shock it apart).

ChrisN · Mar 22, 2019

Hi Jim

For a non reverse wound spring, the BHI define a good spring as one that still has approximately even spacing to the coils when unfurled so, your spring would not be good. Although the overall diameter is not bad, the inner coils are very closely spaced versus the outer.

As a rule, I replace mainsprings because you can't tell how close one is to failure and so partly, I'm protecting myself from an unnecessary return - mind you, new mainsprings can also fail but, that's bad luck.

I'd also clean the movement first to see if that crown wheel screw frees up but, if that doesn't work then it could be someone has locked it with Loctite 270. In which case, it will need heat to break the bond. I'd try holding an electronics soldering iron (mine goes up to 450C) on the screw head and spread some heat that way. Just be careful (goes without saying😁).

Cheers, Chris

Canuck · Mar 22, 2019

JimInOz
And while the mentors are here..........

I have a stubborn crown wheel screw. I shaped a 300 blade to fit and tried to unscrew it (clockwise) but it wouldn't budge and the 300 screwdriver applies a good amount of force.

I'm reluctant to get too heavy with it in case somebody stronger than me has tried to "undo" it previously.

Any tips on penetrants? heating/freezing? ultrasonic? big hammer?

Turn the bridge, wheel side down, over a bench block, with the head of the screw in a hole on the block. Use a staking tool punch that is a tiny bit smaller than the tip of the screw which will protrude through the plate. A light tap with a small riveting hammer on the tip of the screw, and try it again.

Archer · Mar 22, 2019

I replace the mainspring in every watch I service. I would never put a blued steel spring back in. The only exception (and it's very rare) is when a new alloy spring can't be found.

As for the stuck screw, I agree with Chris - run it through the cleaning machine and see if that helps.

Cheers, Al

JimInOz · Mar 22, 2019

Thanks for the tips gentlemen. A new mainspring is on the way, along with a new balance staff.

After 15 minutes in a hot ultrasonic bath I tried again and after slightly more pressure than I'm used to it gave. So next is balance staff replacement and balance poising, but I'll leave that for a few days.

We're off to the hill country to celebrate a birthday so no watch work until I'm well recovered.

verithingeoff · Mar 22, 2019

Have a great trip Jim

Archer · Mar 23, 2019

Glad the new mainspring is coming in, and that you got the screw broken loose.

Broken mainspring can cause a lot of damage depending on the watch, so replacing the spring is something that all service centers and most watchmakers do as a matter of routine. I've received some watches in recently with broken mainsprings, and the first is a Panerai 112, where the spring broke near the inner coil:

Broken area of the spring:

Mainsprings often let go at their most stressed state, so when the watch is fully wound or close to it. When the spring is fully wound in this watch, the spring is coiled around the barrel arbor. When the spring breaks it rapidly uncoils, and the only thing that stops the expansion is the inner wall of the barrel arbor. When it expands to fill the barrel, it slams up against the barrel wall, and this imparts a torque to the barrel, causing it to rotate. The barrel teeth are engaged with the teeth on the center wheel, so the barrel can't turn, and in some cases this results in the barrel teeth taking damage:

The barrel is made of brass (rhodium plated) and the teeth on the center wheel the barrel teeth mesh with are steel, so the barrel takes the damage. In some cases though the forces can be carried further down the wheel train, so this is a Nomos I'm working on right now that also had a broken mainspring - again the barrel teeth suffered:

Again the barrel is brass and the center wheel pinion is steel, but the wheel portion of the center wheel is brass, and those teeth also took some damage:

New parts will arrive from Nomos on Monday...but the point is the mainspring is a consumable item, so it really should be replaced at every service. As Chris points out you generally never know how long the spring has been in the watch you are servicing, and you don't know what life it has left.

Cheers, Al

Theluglife · Mar 24, 2019

@Archer

Archer
Glad the new mainspring is coming in, and that you got the screw broken loose.

Broken mainspring can cause a lot of damage depending on the watch, so replacing the spring is something that all service centers and most watchmakers do as a matter of routine. I've received some watches in recently with broken mainsprings, and the first is a Panerai 112, where the spring broke near the inner coil:

Broken area of the spring:

Mainsprings often let go at their most stressed state, so when the watch is fully wound or close to it. When the spring is fully wound in this watch, the spring is coiled around the barrel arbor. When the spring breaks it rapidly uncoils, and the only thing that stops the expansion is the inner wall of the barrel arbor. When it expands to fill the barrel, it slams up against the barrel wall, and this imparts a torque to the barrel, causing it to rotate. The barrel teeth are engaged with the teeth on the center wheel, so the barrel can't turn, and in some cases this results in the barrel teeth taking damage:

The barrel is made of brass (rhodium plated) and the teeth on the center wheel the barrel teeth mesh with are steel, so the barrel takes the damage. In some cases though the forces can be carried further down the wheel train, so this is a Nomos I'm working on right now that also had a broken mainspring - again the barrel teeth suffered:

Again the barrel is brass and the center wheel pinion is steel, but the wheel portion of the center wheel is brass, and those teeth also took some damage:

New parts will arrive from Nomos on Monday...but the point is the mainspring is a consumable item, so it really should be replaced at every service. As Chris points out you generally never know how long the spring has been in the watch you are servicing, and you don't know what life it has left.

Cheers, Al

Archer, are mainsprings a difficult part to source for vintage watches? Or are they pretty generic and shouldn't be a problem for a good watchmaker?

Archer · Mar 24, 2019

T Theluglife
Archer, are mainsprings a difficult part to source for vintage watches? Or are they pretty generic and shouldn't be a problem for a good watchmaker?

It depends entirely on the watch in question - some are plentiful, and others are not. In some cases if you can't find an exact match, you can find something close that will work - some dimensions on a mainspring allow for significant leeway, and others not so much.

JimInOz · Mar 27, 2019

New mainspring arrived.

Anybody see a problem?

Looking closer.

That's it for today, I'm going to get a cold beer to cool me down!

verithingeoff · Mar 27, 2019

B$#@%@%d🤦

Archer · Mar 27, 2019

On modern mainsprings, the tang end is often a separate part that is welded to the main part of the spring. I can’t see enough to be sure, but I do see what appears to be a spot weld (heat affected zone) on the tang in the last photo, so the spring may be okay...

JimInOz · Mar 27, 2019

Thanks for that Al (and Doug and Chris). It seems to be the method for fabricating the hook now.
Bend it until it almost breaks and then spot weld it.
Donald would be spinning in his grave.

So Geoff, we can proceed. I've just finished cleaning my cleaning machine so will be putting all the parts through an ultrasonic to lift the dirt and then into the cleaning machine for a good wash/rinse/rinse/dry cycle.

verithingeoff · Mar 27, 2019

Sounds good

Mainspring - Re-Use or Replace?

JimInOz

JimInOz

verithingeoff

jimmyd13

ChrisN

Canuck

Archer

JimInOz

verithingeoff

Archer

Theluglife

Archer

JimInOz

verithingeoff

Archer

JimInOz

verithingeoff

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