For decades, drive belts, V-belts, multi-vee-belts, and serpentine belts have been used to transmit power from the engine crankshaft pulley to accessories, like the power steering pump, air conditioning compressor, water pump, or cooling fans. Toothed timing belts and timing chains, too, are accustomed 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 item reliably, slipping 
and producing sound. Conversely, an excessively tight belt may cause accessory or pulley bearing harm. Various forms of tensioner pulley preserve long-term engine and accessory quietness and reliability.
Tightening or Loosening
Sometimes, maintenance or restoration will demand tightening or loosening a tensioner pulley. Changing a drive belt or timing belt, for instance, would need you to loosen a tensioner pulley to make room for the brand new belt, as the new belt is smaller than the worn drive belt.
You will have to tighten a tensioner pulley, generally, after the installation of a fresh drive belt, or to change for a stretched drive belt that hasn’t worn enough to warrant replacement. Stretch out belts don’t require tensioner Car Pulley Belt 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 groups: accessory-integrated (AI) and non-accessory-integrated (NAI). Think of AI tensioners as adjustable add-ons, 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 will be the simplest, most common, and least prone to failure. There can be one caveat, nevertheless, as mechanical tensioner pulleys need manual adjustment. This makes them prone to user error, resulting in insufficient or excessive belt tension. Additionally, they need to be adjusted to pay for belt stretch as time passes.