Seth Thomas Giant No. 1
September 10, 2007 . by BillI just overhauled a Seth Thomas “Giant No. 1″, having an oak case 25-1/4 inches tall (job no. 4433). The movement is marked “8 1/4″ but it is the same movement later called No. 89. It has between-the-plates escapement, and the plates measure 5-5/8 inches tall and 3-5/8 inches wide.
According to a repair label, it had been repaired in 1979. It had two of the overpowering USIBEL FRANCE mainsprings, 0.0180 and 0.0185 inches tick, for the time and strike, respectively. 
Both mainwheels had quite noticeable tooth wear. The strike mainwheel had about twice the wear of the time mainwheel, so I turned the strike mainwheel over so the unused tooth surface could be employed. I judged that the time mainwheel would work okay as is. The time second wheel had quite a bit of wear, so I turned it over.
The previous repairer had installed 2.7 mm tall KWM bushings, which I replaced with 1.8 mm tall KWM bushings (except for the verge pivots, which get 1.4 mm high bushings). I polished the train wheel pivots before installing new bushings.
I discarded the too-strong mainsprings and used the following springs:
Time: 3/4 x 0.0155 x 96 inch Merritt’s mainspring
Strike: 3/4 x 0.0165 x 96 inch, from R & M (or Merritt’s brown box)
Even with this thin mainspring for the time side, the pendulum motion is excellent, the running arc being about 3 times the escape arc. 
Note: I first tried a .0155 inch thick spring for the striking. The striking did run for at least 9 days, but the striking sounded slow, and the customer decided he wanted a faster strike. The 0.0165 inch thick spring should not cause excessive wear, but time will tell. It will certainly be better than the .0185 inch thick mainspring!
