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 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 at all, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making sound. Conversely, an excessively limited belt may cause item or pulley bearing harm. Various kinds 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 need you to loosen a tensioner pulley to make room for the brand new belt, as the brand new belt is Car Pulley Belt smaller compared to the worn drive belt.
You’ll need to tighten a tensioner pulley, in most cases, after the installation of a new drive belt, or even to adjust for a stretched drive belt that hasn’t worn enough to warrant replacement. Extend belts don’t require tensioner pulleys but are “stretched” into place using 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 components, such as an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and several methods to loosen them.
Mechanical tensioner pulleys are the simplest, many common, and least susceptible to failure. There is definitely one caveat, however, as mechanical tensioner pulleys need manual adjustment. This makes them susceptible to user error, leading to insufficient or excessive belt stress. Additionally, they need to be adjusted to pay for belt stretch over time.