I'm not sure about the '97. I have an '03 5.4L Expedition. I replaced the alternator last week. I didn't do anything to the tension of the belt. If your belts were loose to begin with, I could understand that. But if they weren't loose before you pulled the alternator out, they should not be loose after. On the '03 the alterernator is a 1 man job and does not require any belt tighten/loosen.