I had replaced my 6 cog freewheel early this week and despite all the deraileur adjustments I made, it was noisy and rough. Did a search here and learned that if a cog is that old and worn down, the chain might be as well. Found a link in a post to sheldon's site, measured my chain by his method, and my chain was off by 1/8th". Replaced it today and everything works great! Thanks for sharing all the mechanical tips everyone. Lotsa knowledgeable and helpful folks here!