Without a year and engine size, there's no way to be definitive with an answer.
If the car is newer, say post 1993 or so, it's likely to have a serpentine belt - one belt that drives the accessory devices like water pump, alternator & Power Steering.
If it's older and has a dedicated belt, the basic idea is to loosen the alternator PIVOT bolt and pry the alternator outwards against the belt - tighten the pivot bolt to lock it in.
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routing for serpentine belt 2003 mercury sable
There is a tensioner bolt that is connected to the alternator. You have to screw in the bolt, which will pull the alternator out and tighten the belt.
Serpentine belt? You may have to remove to tighten alternator
You cannot adjust the tension on this, it has a spring inside of it. If it is weak, it must be replaced.
To tighten the alternator best on a 240sx, loosen the bolt on the alternator on the drivers side. Pull on the alternator away from the engine to adjust the belt. When it has no more than a quarter inch of give, tighten the bolt to finish.
how do u tighten up an alternator belt on a 1987 BMW 325i?Answerhow do u tighten up an alternator belt on a 1987 BMW 325i?
There is NO TIMING BELT on a 1995 Mercury Sable * Both the 3.0 and the 3.8 liter V6 engines in a 1995 Mercury Sable have a timing CHAIN
depending on the style of belt, on the alternator belt there is an adjustment just below the slider holding the alternator, you just simply tighten it until belt becomes tight.
if the car doesn't have an automatic tensioner than if the belt is around the alternator pully you loosen the bolt holding the alternator on and move the alternator to tighten the belt.
You'll probably want a manual for this, but you may be able to locate a bracket on or near the alternator that moves the alternator itself or a pulley that the belt runs on. This is a tensioner and turning the bolt one way or the other will tighten or loosen the belt. DO NOT OVER-TIGHTEN THE BELT! This will damage the components the belt runs on.
What kind of car? On an older car you just loosen the alternator and pull it until the belt is tight and then tighten the bolts back. On newer cars, there is a tensioner that pulls the slack out of the belt.
Loosen alternator remove old belt. Reroute new belt, tighten alternator.