about 6 months ago i replaced my serpentine belt because it was about 5-6 years old and was developing hairline cracks on the inside. the tensioner seemed ok at the time and it was also only 5-6 years old. water pump is about 4-5 years old.
during cold weather, something from the engine started ticking when everything was cold, and the noise went away after about 4 miles. i checked the belt and pulleys. everything seemed ok except the idler pulley bearing was sort of clicky sounding and the tensioner pulley bearing was a little ringy (or vice-versa i don't remember). i replaced the idler pulley first. no help. next i replaced the tensioner pulley and it seemed to fix it for about a month, until i cranked the truck up one cold morning and it started clacking. the sound was coming from the tensioner area and the belt was slipped off rearward one rib. also, the bolt holding the pulley was loose. i tightened the bolt and put the belt back on and all seemed ok for another month.
so this morning its cold and its ticking again and the belt had slipped off one rib again. i put the belt back on and cranked it up and watched it. when it was on the pulley it was clacking. then it slipped back off one rib and the noise changed from a clack to a click. so i wondered if maybe i'd put the pulley on backwards, so just to check, i removed the pulley, checked the bearing (ok), and flipped it over. i put it back on and the pulley bolt stripped out the threads in the aluminum housing. damn. i cobbled it back together with a 2 inch long 5/16 bolt, nut, washer, etc so i could drive it to work. it still had the same problem, clacking when the belt was seated in the pulley, and then clicking after it jumped out one rib. i got a new tensioner from o'reillys for about $66 and put that on to fix it. its running true and not clicking or clacking. i still don't know what's actually wrong with the old tensioner, but somethings causing it to make noise and be out of alignment.
here's how to replace it:
use a not-too-big ratchet and shallow 15mm socket to rotate the tensioner inward and remove the belt from the alternator pulley first. try to prevent the belt from coming off the other pulleys.
disconnect the electrical plug and the distributor wire from the coil and move them out of the way.
look at how the coil is mounted to a U-shaped bracket. don't remove the coil from the bracket. instead loosen the 2 bolts that hold the U-bracket to the block. remove the top bolt, loosen the bottom bolt and rotate the coil bracket down out of the way. 15mm socket
use a 15mm wrench to remove the nut from the rear stud of the tensioner and remove the assy. save the nut because you have to reuse it.
put the new assy on. make sure the tab goes in the slot of the mounting bracket.
rotate the coil bracket up. reinstall top bolt. tighten both.
rotate tensioner inward and install the belt. i found it easier to fit the belt over the tensioner pulley first, put the socket over the tensioner and rotate it in, then slip the belt over the alternator last. check each and every pulley for alignment before starting it up.
here's some old pictures.