When do you replace a timing chain on a 2002 Saturn SL2?

A timing chain typically doesn't need to be replaced until you tear down the engine for a rebuild.

Unlike a timing belt, which is operated dry, the timing belt is in an oil bath and will last much longer.

If your engine needs a valve job, rings, oil pump or any other components that require a "tear-down", that would be the right time to replace the timing chain, sprockets and chain tensioning rails.