Seth Thomas Sonora chime

If all else fails, try measuring the old one. Width and thickness are somewhat more important than the exact length. You'll need a micrometer or some similar instrument to get the thickness right.

M Kinsler

 

My records from one that I serviced indicate that the Sonora unit spring is 1" x 0.022" x 130". It will put the best spring winder to the test!\

Timesavers No. 23137 is listed as a replacement for the Sonora spring 1" x 0.022" x 136"

RC

 

I also have a spring chart (not sure where it came from) that says 1" x .0228" x 130". I believe the 1 7/8" width has to be an error, the barrel isn't close to that wide.

RC

 

Holy smoke. I've heard about the Sonora (here) but know nothing about them. That mainspring sounds like a real champ.

M Kinsler

 

Yes, and I'm not sure why. The Sonora is basically just a stand alone chime movement, and shouldn't need any more power than a typical chimer. There must be a reason for that big honkin' spring, but I don't get it.

 

It does seem to require a lot of power. If you look closely at the chime hammer assembly you will see a very short moment arm between the hammer arbor and the chime drum and rather long hammer arms with relatively heavy hammers and the hammer lift is also rather high. Also the hammers are directly lifted by the chime drum instead of by an intermediate lever or lifter. I think that just adds up to a lot of required torque to turn the chime drum. My observation is that it really needs all that power. Thank goodness ST include a gear reduction winder.

RC

 

I'll be. Were the reduction gears for that inside the clock case?

M Kinsler

 

Yes. The Sonora winder shaft is at about 3:00 o'clock. The shaft extends to the Sonora unit in the back of the clock and terminates in an open pinion gear that drives a gear to wind that monster spring.

RC

Here are a couple pictures showing the Sonora gear reduction winder system. At least ST included a very substantial click.

 

Mark, see pictures added to post #10 above.

RC