The tensioner is a spring-loaded device consisting of eight basic parts.
      1. Base: stationary part of the tensioner that is bolted to engine block
      or other accessories. Base designs vary. Some base components may be very
      complicated, including large sections of bracketry or seals that form part
      of the cooling system.
      2. Damping Ring: a composite ring that smooths system vibration. When it
      wears the tensioner needs to be replaced.
      3. Tension Spring: preloaded at the factory. It provides force to tension
      the belt.
      4. Arm: connects spring to tensioner pulley. Usually an aluminum casing.
      5. Pulleys/Bearings: are nylon or steel and may be grooved, flat or flat
      with flanges. Pulley surfaces should be inspected regularly for damage or
      wear. The key component of a pulley is the bearing. For a pulley to
      function properly, the bearing must be properly lubricated. The most 
      frequent cause of pulley failure is loss of lubrication in the bearings.
      Do not attempt to put new bearings in an old pulley.
      6. Dust shield: protects bearing from elements.
      7.Bolt: connects pulley to arm.