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, such as the power steering pump, air-con 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, based on engine design.
The drive belt, timing belt, or timing chain won’t work well, or for lengthy, if at all, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making noise. Conversely, an excessively restricted belt may cause accessory or pulley bearing harm. Various types of tensioner pulley preserve long-term engine and item 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 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 to adapt for a stretched drive belt that hasn’t worn enough to warrant replacement. Stretch out belts don’t Car Pulley Belt require tensioner pulleys but are “stretched” into place utilizing a special tool-always use the special tool to prevent belt damage.
Tensioner pulleys generally fall into two classes: accessory-integrated (AI) and non-accessory-integrated (NAI). Think of AI tensioners as adjustable add-ons, 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, most common, and least susceptible to failure. There is usually one caveat, nevertheless, as mechanical tensioner pulleys need manual adjustment. This makes them susceptible to user error, leading to insufficient or excessive belt stress. Additionally, they have to be adjusted to compensate for belt stretch as time passes.