The only S.Y. derailleur that I have seen has the words ‘Yamashita Japan’ stamped on its inside parallelogram plate. Coincidentally, I acquired a Sun-Bow derailleur with a brown card label attached to it saying ‘Yamashita Iron Works Ltd. YA-100 Rear Derailleur’. This Sun-Bow also shares some small parts with the S.Y. derailleur.
Based on these tiny crumbs of evidence, my pitiful researches on Google have thrown up two possible companies who may possibly have manufactured the S.Y. brand.
- The first of these is the Yamashita Manufacturing Company based in Sakai, Japan the home of Shimano and SunTour. This company was established in 1902 as the Yamashita Ground Metal Shop (!?) and started producing bicycle components in 1947. In 1973 the company appears to have changed its name to Koyo Giken Company Ltd, and then to have established Koyo Engineering Company Ltd in 1980. It also appears that, in 1973, it changed its main business to producing engineered parts for furniture - and so it is possible that the manufacture of bicycle components died out at this point. Koyo Corporation exists to this day. It has a history page on its web site. It has been suggested to me that the ‘S’ in the brand name is for Sakai, and the ‘Y’ is for Yamashita - but I don’t know if this is true.
- A company called Yamashita Iron Works was established in 1931 in the Nishiyodogawa ward in Osaka, about 20 km from Sakai. Shimano also started out (in 1921) called Shimano Iron Works and SunTour started out (in 1912) called Maeda Iron Works. In 1968 Yamashita Iron Works spun off Yamashita Machinery Co. Ltd. a maker of industrial handling equipment which seems to continue to have a serious business supplying production lines to Toyota, amongst others. Yamashita Machinery Co. Ltd. also has a web site.
The strength of the first possibility is that the company definitely made bicycle components in the relevant period. The strength of the second possibility is that the company definitely had ‘Iron Works’ in its name.