Originally Posted by khuon
One thing to note about replacing chains. A really worn chain will also wear the cassette and chainring. When you replace a chain that has worn to such a condition with a new chain and mount it onto a drivetrain that's been equally worn, the new chain will also "wear" in to a condition that will almost be as bad as your old worn chain. For this reason, it's advisable to replace both the chain
and cassette/chainrings when the gears have shown signs of considerable wear. Inspect the teeth of your gears. Look for "sharktooth" shaped teeth and the chain not seating correctly into the teeth. See
Sheldon Brown's article on chain and sprocket wear.
Maybe I should have only used the adjectives "old" and "rusty", as the chains don't really have much wear in them at all. Both of these bikes were the type that the original owners purchased, rode twice, and then hung in the garage from the rafters. Both bikes still have lots of gear left on the cassette and rings.