Easy, if the belt tension is good to drive the alternator and engine accessories it's ok. If the belt does not maintain proper tension, or it's making noise replace the tensioner. There is no user adjustment. I like the NAPA part as oem replacement.
I belive that there is no adjustment on the serp belt on your lumina. Should be a spring loaded tensioner. If you are having problems with the belt slipping you most likely need to replace the belt/ tenssioner.
The 1990 has a chain. The 1991 has a belt.
Chain
It has a serpentine belt that runs all the accessories not just the fan
Timing chain.
bad retractor
http://wiki.answers.com/Q/How_do_you_mount_a_serpentine_belt_on_a_chevy_lumina"
it doesn't have one
usually serpentine belts get their tension(tightness) from the belt tensioner
the single belt that runs around the engine, alternator, a/c and water pump is the serpentine belt.
The 1993 Chevy Lumina 3.1 liter engine timing belt can be found on the front of the engine. You will need to remove the front engine cover in order to access the timing belt.
First and foremost, make sure you have a diagram before removing the old belt. If there isn