For many years, drive belts, V-belts, multi-vee-belts, and serpentine belts have already been used to transmit power from the engine crankshaft Car Pulley Belt pulley to add-ons, 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, based on engine design.
The drive belt, timing belt, 
or timing chain will not work well, or for lengthy, if, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making noise. Conversely, an excessively limited belt may cause item or pulley bearing damage. Various forms of tensioner pulley keep long-term engine and accessory quietness and reliability.
Tightening or Loosening
Sometimes, maintenance or repair will demand tightening or loosening a tensioner pulley. Replacing a drive belt or timing belt, for instance, would need you to loosen a tensioner pulley to make room for the new belt, as the new belt is smaller than the worn drive belt.
You will have to tighten a tensioner pulley, in most cases, after the installation of a new drive belt, or to adjust for a stretched drive belt that hasn’t worn enough to warrant replacement. Stretch out belts don’t require tensioner pulleys but are “stretched” into place using a special tool-always use 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 accessories, such as for example an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and several ways to loosen them.
Mechanical tensioner pulleys will be the simplest, the majority of common, and least susceptible 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 extreme belt pressure. Additionally, they have to be adjusted to compensate for belt stretch as time passes.