Joined: Jan 2010
Posts: 9,814
Likes: 1,790
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I bought a ~1991 Torrelli with a Athena-copy Xenon gruppo that indexed 7s perfectly.
I later put a larger 13-25t 7s Sunrace freewheel on, replacing the Regina 7s, and the indexing really suffered, couldn't get it adjusted right.
I then put a Shimano 9s chain on, and the shift action was again quick to shift and silent in every gear.
What worked poorly during the Synchro years just might work well with modern, narrower chain fitted.
Having said all that, it is easiest to start with a Synchro-equipped bike that is already shifting properly but with room for improvement that a modern, narrower chain just might enable.
Much like any Suntour U-7 or Accu-7 setup, that would be greatly improved just by using Shimano 9s chain.