The Sun-Bow YA100 is a gruesome, Frankenstinian copy of an early SunTour Honor.
It has the folded steel knuckles, the ribbed black plastic spring cover and it has a jockey wheel that can be removed with a (plastic) wing-nut - all of these echo SunTour features of the late 1960s and early 1970s. Most disturbingly it has a slant parallelogram - but the slant is so slight that you can barely detect it - perhaps Sun-Bow were hoping that it would pass unnoticed by SunTour’s eagle-eyed patent attorneys.
What the Sun-Bow YA100 conspicuously lacks is any sense of composition, coherence or quality. Both the b-knuckle and the p-knuckle are oversize pieces of bent steel sheet, while the parallelogram is weirdly undersized. The edges are rough and the corners sharp to touch. All of this is particularly strange, because composition, coherence and quality were exactly the qualities that marked out other Japanese derailleurs of the time.
I have dated all my Sun-Bow YA100 derailleurs at 1977, because this is the date of the three related patents.
This particular Sun-Bow YA100 displays the following distinctive features:
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