Replacing a serpentine-belt idler pulley on a 4.3 liter V-6 Chevy is a moderately challenging job, depending on the year and model of your Chevy. The idler pulley routes the serpentine belt from one accessory pulley to the next while ensuring the correct angle of deflection on each pulley for the proper amount of torque necessary to turn the pulley at the right speed. In the event the bearing ring inside the idler pulley fails, replacement will be your only option. If you possess basic automotive-repair skills, you can replace the idler pulley in less than 30 minutes.
Plug the end of the belt-tensioner tool into the belt tensioner. You can locate the belt tensioner by following the serpentine-belt routing diagram, printed on a sticker located on the fan shroud.
Move the belt tensioner aside with the belt-tensioner tool and then slip the serpentine belt off the idler pulley with your other hand. Let the belt tensioner move back into its relaxed position.
Remove the mounting bolt from the center of the idler pulley with the socket set. Lift the idler pulley out of the engine bay and position the new idler pulley in its place.
Thread the mounting bolt through the center of the new idler pulley and into the front of the engine by hand. Tighten it down with the socket set.
Move the belt tensioner aside once more with the belt-tensioner tool and then move the serpentine belt over the new idler pulley. Hold the belt in place with your hand while you slowly move the belt tensioner back against the belt with the tensioner tool.
