Depends on the age of the car.
On older models with the plain V-belt, slacken the alternator then lever it away from the engine using a length of wood ON THE MOUNTING BRACKET END until the tension is correct, then tighten the bolts. DONT lever it on the free end of the alt, you will damage it.
You might need someone to help with this, it's a bit of a juggling act trying to do it solo.
If it is a later model with power steering and a ribbed V-belt, it has a spring-loaded automatic tensioner and cannot be adjusted.
If the belt is slack either-
The tensioner is broken, incorrectly fitted or worn.
You have the wrong size belt.
The belt is not routed correctly.
one of the parts driven by the belt is incorrectly fitted, is the wrong part or has the wrong size pulley fitted.
vaux, December 2009
