For decades, drive belts, V-belts, multi-vee-belts, and serpentine belts have been used to Car Pulley Belt transmit power from the engine crankshaft pulley to accessories, 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 well, or for very long, if, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and producing noise. Conversely, an excessively tight belt may cause item or pulley bearing damage. Various types of tensioner pulley keep long-term engine and accessory quietness and reliability.
Tightening or Loosening
Sometimes, maintenance or restoration will require tightening or loosening a tensioner pulley. Changing a drive belt or timing belt, for instance, would require you to loosen a tensioner pulley to make room for the brand new belt, as the brand new belt is smaller sized compared to 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 belts don’t need tensioner pulleys but are “stretched” into place utilizing a special tool-always use the special tool to avoid belt damage.
Tensioner pulleys generally fall into two types: accessory-integrated (AI) and non-accessory-integrated (NAI). Think about AI tensioners as adjustable components, such as for example an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and many methods to loosen them.
Mechanical tensioner pulleys will be the simplest, many common, and least prone to failure. There can be one caveat, nevertheless, as mechanical tensioner pulleys require manual adjustment. This makes them susceptible to user error, leading to insufficient or extreme belt tension. Additionally, they have to be adjusted to compensate for belt stretch over time.