Hello,
Do you think that a too short mainspring can make a watch run fast. The end broke off the new spring about 3/4 inch from the end so I tried heating it and bending a new tongue. Which to my surprise worked. But it runs fast I demaged the watch checked the hairspring etc and all looks good. So I am suspect of the MS. Any thoughts?
It could. A shorter spring will mean less power reserve. Also, as the dimensions of a mainspring are critical to the running of the watch and are mathematically linked to various components, you may notice less power to the escapmement as the watch unwinds, which can cause lower amplitude and a faster rate in the last half of the power reserve. 3/4 inch is not that much, but it would be noticeable. My advice would be get a watchmaker to have a close look at it on the timing machine to see how it is running, you may have other issues as well, particularly if the watch hasn't been serviced in awhile. I assume you cleaned and lubed the mainspring when you put it back in the barrel? A dry, dirty mainspring can stick. It really depends on the watch. Mainsprings are still available for most old calibres.