Is my serpentine belt not tight enough?

I just replaced my alternator and I’m not sure exactly how tight the belt needs to be to make the alternator work properly. The belt feels pretty tight but I noticed the tension bolt has a clean / shiny part of the screw still sticking out and everything else is rusty from exposure. The car is 22 years old. Do I need to tighten the screw more so I can’t see the clean / shiny part? I’m guessing yes but I want to be sure. Thanks!

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  • Barry
    Lv 5
    2 months ago
    Favourite answer

    The old belt was stretched so the bolt was further in. The test for belt tension is to deflect the longest run by 15mm (1/2") with thumb pressure. Don't be tempted to overtighten or you will just burn the bearings out.

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  • M.
    Lv 7
    2 months ago

    You tighten it according to the new belt, not the old belt.  The new belt is likely shorter.  If your alternator has a fan on it, grab it with your fingers (engine off) and try to turn it.  If it turns, tighten it a bit.  If you make the belt too tight then all the bearings and bushings related to the devices that the belt is turning will wear faster.  It's rather difficult to say how tight using words.

    Check the belt tension in a few weeks because the new belt does a little bit of stretching right after you install it.

    If ever the belt squeals when you first start the car, tighten it a bit.-General automotive mechanic since 1972

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  • 2 months ago

    You shouldn't be able to press and deflect the belt more then 1/16" to 1/8" in the longest stretch between pulleys. It's hard to over tighten a serpentine belt.

    Source(s): Mitsubishi Master Tech
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  • Sky
    Lv 7
    2 months ago

    In addition to the deflection checks the other answers have recommended, another thing to check is, does the belt squeal when under load?  If a heavy electrical load on the alternator creates enough drag to make the belt squeal, that's an indicator you need to tighten it.

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  • Anonymous
    2 months ago

    Check tension.  A sag of not more than 1/4 inch midway of the belt when pushed with your thumb means the belt is tight enough.

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