mr.

[rickyb]

I took apart a nice old English Fusee watch and noticed the mainspring was broken. I have been trying to find a replacement but with no success. Cousins do not have the exact dimentions. is there a way i could substitute it for another one that is close to size? the dimmentions that i need are 2.5 mm x .25 mm x 460 mm X 16 mm (inside baril dimention).

If somebody could help me out it would be greatly appreciated. 

Rick

[watchweasol]

Hi  finding parts for some of these old pocket watches is a nightmare, I have been looking for a pallet/fork for over a year, GR parts are you best bet or get as close to your measurements as possible remembering its got to fit in the barrel and the cover has to go on, therefore as regards height always go for the one that is less than the old one, lenght again get as close as you can but again err on the lesser side, wish you luck on your quest.

[Endeavor]

Have you tried the spring-calculator? https://www.vintagewatchstraps.com/mainsprings.php

There is a chance that the spring you took out and use as a reference may not be the original anymore (?)

You have to have the height correct, else it doesn't fit in the barrel. Than you have to have the end of the spring (Bridle) right or be able to make it fit. A barrel with a hook (TR) will take a  Normal Bridle.

Also, modern spring may be a bit more stiff (read: more powerful). Start with the closest you can find and proceed from there ...

Perhaps forum member @JohnR725  can give you a better advice ?

Edited November 6, 2019 by Endeavor

[JohnR725]

On 11/4/2019 at 10:33 AM, rickyb said:

English Fusee watch

The problem with fusee watches are there usually old really old. For instance some times when you look at the back sides of the plates you'll see the scribe marks used for drilling the pivot holes. So basically watches of this age are almost hand made or basically a lot of the parts are hand fit.  This means that finding replacement parts is going to be challenging if not impossible.

Fortunately the mainsprings were probably made by somebody else so they will fit within specifications sort of. You didn't mention the type of end usually they got creative and their very different than modern Springs. So if you are going to have to fabricate an end then you can go to a much longer spring and cut to size. Also as mentioned above modern Springs are typically stronger for the same thickness so we can go lighter but are basically are stuck getting whatever you can get.

So rather then me giving numbers out of my catalog you can go to the cousins website I did a search for mainsprings. Then the mainspring catalog is broken up in the sections this is the section you're looking for to download. "GR Mainsprings, No. 6046 to 6800 (1339KB)".  Then scroll through the pages until you get the width of 2.5 mm as you specified above.

So now we make some assumptions like standard end type because you didn't specify. The length if you don't want to shorten and make your own looks like 460 mm is in the list and probably could go to 480 mm.  So we Start with the strongest thickness and go backwards looks like our first spring will be 6702. But I notice there's two of them with the same number one of them has a T end which I suspect is not what you want.  Then the reason for looking at the catalog section is just because it's listed doesn't mean it exist anymore. So you may have to go through looking up quite a few of the numbers to find one that hopefully is still available.

[rickyb]

Thank you so much John for the precious insight. The end is just folded over. But there is a protrusion in the barrel, so I suspect a mainspring with a hole could do. Will a different sized mainspring afect the keeping of time? 

Thanks again Rick.