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Greg Crockett
11-02-2002, 06:31 PM
I have my 19.5 ligne Chrono (w/a British name on the dial) all appart. Under one plate, I see it's a Montbrillant Swiss brand.

The question is the broken main spring.

The main spring is a Dennison size 11Wide, strength 1/2, by 21 inches long. The closest spring I have is of Dennison strength 3 (other dimensions are about the same). This is clearly not as strong as the original spring. Ordinarily I would put it in and see how it goes. However, with the chrono complications, I would rather not take it appart more than once. What does collective experience advise regarding the interchageability of a Den 3 for a Den 1/2 strength main spring?
Greg Crockett
11-02-2002, 06:31 PM
I have my 19.5 ligne Chrono (w/a British name on the dial) all appart. Under one plate, I see it's a Montbrillant Swiss brand.

The question is the broken main spring.

The main spring is a Dennison size 11Wide, strength 1/2, by 21 inches long. The closest spring I have is of Dennison strength 3 (other dimensions are about the same). This is clearly not as strong as the original spring. Ordinarily I would put it in and see how it goes. However, with the chrono complications, I would rather not take it appart more than once. What does collective experience advise regarding the interchageability of a Den 3 for a Den 1/2 strength main spring?
Greg Crockett
11-03-2002, 05:31 AM
The sample looks original. I don't think this watch has ever been taken appart before.
Steve Maddox
11-04-2002, 08:14 AM
Greg,

Chances are, your watch probably needs the stronger spring. Just a small difference in the thickness of watch springs makes an exponential difference in their strength, and in your case, the difference is significant. I think your chronograph will have a greatly diminished balance motion if you try to use a #3 spring where a #0 is correct.

Your best option would probably be to order a spring of the correct size, but if that's not available (and some aren't), you may have to try to get by with something that's as close as possible. For what it's worth, rather than trying a spring that's significantly too thin, you'd be better off trying one that's just a bit too narrow, but of approximately the same thickness.

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Steve Maddox
President, NAWCC Chapter #62
North Little Rock, Arkansas