Favre Leuba 255 Twin Power Fitting New Mainsprings

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Hi. Just serviced a very slim Mappin and Webb 1970s gold dress watch. This is a 25 years service presentation watch which jeweller's used to supply back in the day. To my delight it had a Favre Leuba twin barrel 255 hiding inside - my favourite movment. A deeply clever design and a joy to work on. Despite clear evidence of at least two services, it ran at very poor amplitude. However the trace was clean so after a good scrub and lubrication the mainsprings were extracted. I've done three of these over the years and every time old mainsprings had been left by servicing watchmakers. This is unfortunate since the layout allows the two barrels to be removed in seconds. Jeweled barrel bridge - posh eh ? The barrel design is unusual because the winding ratchet wheel forms the top cover and arbor thus saving height and complication - see pic. A different approach is needed to replace them which seems to deter servicing watchmakers. The replacements should be 1.50 * 0.07 * 285 at 7.0 mm diameter - GR 4052 will do. The excellent Gleaves & Co supplied mine. The fun starts when you find the central coil is too large for the arbor hook to engage.

I use two methods. The strong cheap flat tweezers fit inside the small barrel and careful squeezing will allow you to tighten that curve enough. The internal post in the barrel will help prevent snapping the spring - be gentle. Plan B is to temper the spring fixing point to a brown colour using a temperature controlled soldering iron and then bend it around a drill shank slightly smaller than the desired end loop size. Both work with patience. Hope that helps guys.