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Thread: How tight is too tight for the serpentine belt on a 4.0L?

  1. #1
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    Oct 2001
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    How tight is too tight for the serpentine belt on a 4.0L?

    Good Day everyone,

    I've searched and done a lot of reading about the belt on the ZJ, and its relation to the water pump failure.

    I replaced my belt about 8,000 miles ago and I'm not sure if I have it tight enough. However, I fear "cranking down" on it because of damage to the accesories.

    So how does one know when the tension of the belt is correct?

    I did the old thumb deflection trick and it seems "right" to me. But my frame of reference with this trick is from GM veichles with an auto-tensioner. How far should be belt deflect? I'm not impressed with the reverese threaded bolt type tensioner on the 4.0L. It leaves huge margin for error and doesn't auto correct the tension as the belt ages (however it is a very tried-and true looking design).

    If anyone can offer any suggestion to this I'd be appreciative. By the way, when it is VERY cold (~0F to -20F) and I start the Jeep and/or make your first stearing turn a schreeching noise like the belt slipping (or the power stearing pump) happens for about 2 seconds maybe 2 or 3 times. Otherwise everything is silent. This is my only suggestion that the belt's tension may be out of spec. Or perhaps an accessory may be failing...I have 81,000 miles on this 1998 ZJ.

    Thanks and have a great day,

    Scott
    1998 ZJ Laredo Selec-Trac 4x4 4.0L
    1998 Jeep Grand Cherokee, Laredo, Selec-Trac 4WD, 4.0 I6.

  2. #2
    Registered John V.'s Avatar
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    Sep 1999
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    California, San Diego, USA.
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    Scott, none of the "hand tests" really work. The belt ends up being about half as tight as it should be (but feels tight as hell). Get a serpentine tension gauge from napa for about $10. It's called a Klick-it or krick-it or something like that. The investment of $10 can save hundreds. I also found that many of the aftermarket belts lose their tension rapidly and require frequent tightening. Regards, John V.

    I found the box it's a Krikit #NBH KR2 is reads "V-Belt tensioning gauge" but it's also for flat belts.

    [This message has been edited by John V. (edited 03-23-2002).]
    John V San Diego, Calif.
    Current wheeling videos

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    Glow-in-the-dark Yellow Rubi LJ, Nth* 6" kit, Auto, 35's with 5:13's
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  3. #3
    Registered David's Avatar
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    Mar 1999
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    South Korea
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    Lightbulb

    I recently replaced my water pump and was very cautious not to overtighten the belt. I don't have a tension gauge, so here's what I did...

    It didn't squeal, so I thought it was tight enough. But when I turned on all of my lights at night, the extra alternator load made it squeal like a stuck pig! Also, the belt was loose enough to *flap* near the alternator. I pulled the airbox for easy access... turned on EVERYTHING... all lights, A/C, etc. and tightened the belt until the squealing just stopped.

    Not very scientific, but it's just tight enough not to squeal under max load and it doesn't flap. Why should it be any tighter?

    ------------------
    ®~David~®
    1994 ZJ 4.0L I6•Flame Red Laredo•Quadra-Trac•Stock Loaded•Eurolamps•Kolak harness•PIAA Super White PlatinumPoweraid TBSEdelbrock IAS Shocks•Full Skids•4 Tow Hooks•Pirelli Scorpion A/T'sV1eTrex Vista GPS
    Korea Jeep Homepage (w/The Jeep Book 1994)
    ~David~
    1994 ZJ 4.0L I6•Flame Red Laredo•Quadra-Trac•Stock Loaded•Eurolamps•Kolak harness•PIAA Super White PlatinumPoweraid TBSEdelbrock IAS Shocks•Full Skids•4 Tow Hooks•Goodyear Wrangler SilentArmorV1Garmin 60CSx GPS

  4. #4
    Registered John V.'s Avatar
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    Lightbulb

    <font face="Verdana, Arial" size="2">Originally posted by David:
    Not very scientific, but it's just tight enough not to squeal under max load and it doesn't flap. Why should it be any tighter?

    </font>
    I'm guessing that you are asking Belt "squeal" is extreme slipping (a great difference between belt and pully). If the belt is too loose the belt may not be squealing but it can still be slipping, greatly speeding up belt wear. Like a tire that is not quite squealing from a quick start or stop, the loose belt is doing that kind of duty for many hours more. If you have a strobe light and some chalk you can mark the belt and some pullys and see the non squealing, but too loose belt creep (sometimes quite rapidly)across the surface of the pully as loads cycle off and on. You could do it without the strobe but it would not be as much fun Squealing belts are really bad, too loose belts are just plain bad. One other thing that can happen, is at high RPM the loose belt can fly off especially so if the AC compressor cycles or the clutch fan engages.

    Regards, John V.
    John V San Diego, Calif.
    Current wheeling videos

    Flop recovery at Gatekeeper Calico -- OUCH!
    http://www.youtube.com/watch?v=osy9XTY1N5A
    Anza Borrego Heart Attack Hill
    http://www.youtube.com/watch?v=_bScAe7rjsU
    Dusy Ersham Trail with 12 Hr tow out
    http://www.youtube.com/watch?v=NuIwv...e=user&search=

    Glow-in-the-dark Yellow Rubi LJ, Nth* 6" kit, Auto, 35's with 5:13's
    And when we have company in town and DD,
    ZJ with mostly home-made armor and 4.75" Franken-lift.

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