For decades, drive belts, V-belts, multi-vee-belts, and serpentine belts have already been used to transmit power from the engine crankshaft pulley to add-ons, like 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, depending on engine design.

The drive belt, timing belt, or timing chain won’t 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 tight belt may cause item or pulley bearing damage. Various types of tensioner pulley keep long-term engine and item quietness and reliability.

Tightening or Loosening
Sometimes, maintenance or restoration will require tightening or loosening a tensioner pulley. Replacing a drive belt or timing belt, for example, would require you to loosen a tensioner pulley to make room for the new belt, as the brand new belt is smaller sized than the worn drive belt.

You’ll need to tighten a tensioner pulley, in most cases, after the installing a new drive belt, or even 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 using a special tool-always use the special tool to prevent belt damage.

Tensioner pulleys generally fall into two types: accessory-integrated (AI) and non-accessory-integrated (NAI). Think about AI tensioners as adjustable accessories, such as an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and many ways to loosen them.
Car Pulley Belt mechanical tensioner pulleys are the simplest, most common, and least susceptible to failure. There is definitely one caveat, nevertheless, as mechanical tensioner pulleys need manual adjustment. This makes them susceptible to user error, leading to insufficient or extreme belt tension. Additionally, they need to be adjusted to compensate for belt stretch as time passes.