A pocket watch mainspring so big that I think it's actually a clock mainspring

[GregG]

Hello all,

I wasn't sure if this belongs in the watch section or the clock section, but here goes.  I am having some trouble finding a suitable replacement mainspring for this pocket watch.  It's a very large New Haven watch with a very large mainspring.  The mainspring is so large that I think it's actually a clock mainspring.  The dimensions are 6.57mm H x 0.28mm T x 710mm L (est.) x 22.8mm barrel ID.

Watch mainsprings look like they top out at the upper 4mm's in terms of height.  Above that, and you've entered the realm of clock mainsprings.  I am able to find clock springs of similar height and thickness, but they're either way too short, or they are meant to fit into much larger barrels.

Can someone point me in the right direction for a replacement?  Also, I do not have a clock mainspring winder, so the replacement would preferably be of a smaller ID so I could pop it right into the barrel from the holder.

Edited October 26, 2021 by GregG

[KarlvonKoln]

Sounds like the watch could be a size 18s or maybe even 20s.  I know a couple places that might have the springs, but I should ask if you can post pictures please.  And the serial number too (you can use a "*" for the last digit if you don't want to post the exact number.  I will still be able to look it up and hopefully find parts numbers too.  That'll hopefully tell us exactly what we ought to look for.

[oldhippy]

From the description it might be a  Goliath. Can you post photos of it please.

[GregG]

There was no serial number I could find on the movement, unless it's hidden somewhere.

Also, now that I'm looking at it again, it doesn't look like a watch, so much as a scaled down clock stuffed into a large pocket watch case.

[oldhippy]

That's not what I expected. Looks like one of those 2 inch movements that you find in some clocks. Have measured across the movement for it's size?  

[GregG]

I haven't, but I will when I get back home.

[GregG]

12 hours ago, oldhippy said:

That's not what I expected. Looks like one of those 2 inch movements that you find in some clocks. Have measured across the movement for it's size?  

I didn't have a ruler handy, so I had to eyeball it.  It's about 1.5 to 1.75 inches across.

[oldhippy]

A clock mainspring is what you need. Get one as close to the dimensions as the broken one. They do not need to be so precise as if it was for a watch. As long as the movement goes for 30 hours is what you need. 

[GregG]

Thanks hippy.

I've searched several watch part sites and haven't found quite the match I need. 

The first site I found https://www.clockworks.com/clock-parts/clock-movement-hole-end-mainsprings.html

1. 6.4mm x 0.28mm x 400mm x MB
2. 6.4mm x 0.28mm x 990mm x 26mm

The second site I found https://perrinwatchparts.com/collections/clock-barrels-and-clock-mainsprings/products/hole-end-clock-mainsprings-4to13mm

1. 6.4mm x 0.25mm x 600mm
2. 6.4mm x 0.28mm x 390mm
3. 6.4mm x 0.28mm x 840mm
4. 6.4mm x 0.28mm x 975mm
5. 6.5mm x 0.25mm x 325mm

And on Cousins I found https://www.cousinsuk.com/product/english-dial-fusee-french-german

1. 5.9mm x 0.24mm x 650mm x 21mm
2. 6.5mm x 0.29mm x 930mm x 25mm

On site number one, the choices are either way too long or way too short.  The barrel sizes are also either too big, or MB (music box), and I'm not sure what that means.  The second site is promising, choice number one and three look nearly compatible but the barrel diameters aren't listed.  And on Cousins, choice number one looks good, but is 5.9mm too much of a difference from the measured 6.5mm?

[KarlvonKoln]

It's built like the little "travel alarm" clocks, except without the alarm part!  And built into a pocket-watch-facsimile of a case, so you could carry it accordingly.  I've heard about those, but this is the first set of pics I've seen of one of them.  OH is bound to know more about these than I do.  Given it's nature, I think I would look for a small clock spring too.

[oldhippy]

Cousins is the only one that is anywhere near. I would try that.  

[KarlvonKoln]

Are the two holes in the bottom for feet?  It looks like something would screw into there.

[GregG]

34 minutes ago, KarlvonKoln said:

Are the two holes in the bottom for feet?  It looks like something would screw into there.

I see what you're saying, but I don't think so.  If you look on the movement, there are pegs that lay across those holes, I think it's for holding the movement firmly.

[KarlvonKoln]

3 hours ago, GregG said:

  If you look on the movement, there are pegs that lay across those holes, I think it's for holding the movement firmly.

I see them now!  So it's held in its case in three places: the pendent is a mounting screw, and there are the two screws at the bottom.  So that means the large hole in the inner cover was for some kind of winding key, and the central hole would be for the setting knob?  Yeah, this really is built like a carefully disguised travel-clock.  Interesting novelty, that.

Edited October 28, 2021 by KarlvonKoln

[GregG]

Correct, the big hole on the left is for the winding key, which I removed to access the mainspring.