That's an old-style 5-speed freewheel. Even a "normal 8-speed chain" is designed for cog spacing tighter than that freewheel provides. You need a - what's the dimension again - 1/8" chain? Like maybe a fixie chain? Edit: 3/32", as more erudite posters point out below...
Alternately, a closer-spaced freewheel, like an Ultra-6, would help.
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1987 Nishiki Prestige (now 650B!)
1981 Trek 710
198? Nishiki Olympic 12 mixte (now 650B!)
2020 Surly Troll fat-tire build
Last edited by ctmullins; 02-08-12 at 06:27 PM.