For many years, drive belts, V-belts, multi-vee-belts, and serpentine belts have been used to transmit power from the engine crankshaft pulley to components, such as the power steering pump, air conditioning compressor, water pump, or cooling fans. Toothed timing belts and timing chains, too, are used to transmit power from the crankshaft to the camshafts, plus some from the camshaft to camshaft, depending on engine design.

The drive belt, timing belt, or timing chain will not work very well, or for lengthy, if, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making sound. Conversely, an excessively restricted belt may cause accessory or pulley bearing harm. Various forms of tensioner pulley keep long-term engine and item quietness and reliability.

Tightening or Loosening
Sometimes, maintenance or repair will require tightening or loosening a tensioner pulley. Changing a drive belt or timing belt, for example, would require you to loosen a tensioner pulley to create room for the new belt, as the brand new belt is smaller than the worn drive belt.

You will have to tighten a tensioner pulley, generally, after the installing a new drive belt, or even to modify for a stretched drive belt that hasn’t worn enough to warrant replacement. Stretch belts don’t need tensioner pulleys but are “stretched” into place using a special tool-always utilize the special tool to avoid belt damage.

Tensioner pulleys generally fall into two types: accessory-integrated (AI) and non-accessory-integrated (NAI). Think of AI tensioners as adjustable components, such as an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and many ways to loosen them.
Mechanical tensioner pulleys are the simplest, most common, and least prone to failure. There can be one caveat, however, as mechanical tensioner pulleys require manual adjustment. This makes them prone to user error, resulting in insufficient or extreme belt stress. Additionally, they need to be adjusted to compensate for belt stretch as time passes.