For decades, drive belts, V-belts, multi-vee-belts, and serpentine belts have been used to transmit power from the engine crankshaft pulley to components, 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, and some from the camshaft to camshaft, depending on engine design.
The drive belt, timing belt, or timing chain won’t work well, or for very long, if, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making sound. Conversely, an excessively tight belt may cause item or pulley bearing 
damage. Various types of Car Pulley Belt 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 create room for the brand new belt, as the brand new belt is smaller sized compared to the worn drive belt.
You’ll need 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 belts don’t need 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 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, most common, and least prone to failure. There is one caveat, however, as mechanical tensioner pulleys need manual adjustment. This makes them susceptible to user error, resulting in insufficient or excessive belt stress. Additionally, they need to be adjusted to pay for belt stretch over time.