There are multiple ways a TJ mounts and adjusts it's serpentine belt. If you have a 4.0 made in 1998-99, this should work for you. Probably works on a '97 but who knows. Later models have newer, better ways of adjustment to include a lever loosened adjustable idler tensioner but this method works just fine and you don't need to buy a lever tool.
My Jeep has 86,000 + (babied). Serpentine belt is splitting (a real warrior though). Time to replace.
Replacement belt (what I bought, others might disagree but it worked):
Gates K060923 Multi V-Groove Belt
Currently about $28U.S. on Amazon
Remove radiator overflow bottle (I had to get my hand underneath to push up to get it to release)
Get a trouble light. Locate power steering pump and look directly below. See adjustment pulley (pictured below). Loosen (do not remove, just loosen) 15mm mounting bolt holding adjusting idler pulley to mount to allow for up/down adjustment of that pulley by adjustment screw, in back (next diagram). Will likely require breaker bar to release bolt. Should be tight.
Once bolt is loosened, you can adjust the machine screw that screws up and down to move the pulley up and down to allow for loosening (to remove belt and install new) and tightening (to re-tighten the belt for operation) Illustration shows 1/2 inch ratchet with 15mm socket at the end of a socket extension. Where the screw had been sitting in the mount for years, it looked a bit dry and a bit rusty. I put a dab of red grease on it before I tightened it back up.
Take off old belt. Have fun running the new one over and around the fan and trying to get it down around the crank, etc., etc. PIA (see my diagram, following, for help with routing the new belt) I had my esposa help hold it in place when I went underneath to get it wrapped on the crank but I'm a wimp. She also helped review the diagram and look at the routing before I started ratcheting the machine screw back down to tighten it.
Make sure you re-tighten the mounting bolt once the new belt is installed AND you tighten the adjusting screw back to approximately where it was when you started and the belt was tight. I ran the engine for a while and re-checked the tension. My tension screw only had a few threads left once it was tight. The youtube video referred to below shows how to check belt deflection.
I also made myself a crude belt diagram to help me install the new belt once the old one was removed. Obviously the fan blades are outside the belt, not inside as drawn. I added the blades for reference only. They should be dotted lines. Try not to laugh.
The best Youtube video (linked below) I found for the job for this year TJ (98-99) after watching a dozen or so. Might be all you need. As funny as my diagram is, it's better than the decal provided in the engine compartment.
https://www.youtube.com/watch?v=HbhVqNO4vYo
