Inspection of the Belt Tension
Some V-belts use a threaded adjustment, and the ONLY accurate way to check belt tension is to use a belt tension gauge. See your Western Star dealer for this type of adjustment.
Serpentine belts are tensioned by spring-loaded idler pulleys that are usually maintenance free. Uneven belt wear can indicate a loose, worn out, or bad bearing on the auto tensioner. A build up of dirt or grime around the front bearing surface of the wheel can indicate a future bearing failure due to inadequate lubrication.
Caterpillar
On Caterpillar engines, there is a red and green decal on the side of the idler arm mount. See Fig.. A properly tensioned belt is indicated by the shoulder of the idler arm aligned with the green zone of the decal. As the belt stretches, the shoulder will drift into the red zone. If the idler arm shoulder moves into the red zone, the belt needs to be replaced.
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Shoulder
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Spring-Loaded Tensioner
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Label Green Zone
Fig. 1, Caterpillar Self-Tensioner
Cummins
On Cummins engines, a properly tensioned belt is indicated by the stop bar being in the center between the idler arm stops. See Fig.. As the belt stretches, the idler arm stop will rotate to the stop bar. If the idler arm stop has rotated to contact the stop bar, the belt needs to be replaced.
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Stop Bar
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Idler Arm Stops
Fig. 2, Cummins Self-Tensioner
Detroit Diesel Series 60
The idler arm pivot on Detroit Diesel Series 60 engines has a pointer cast into the arm. See Fig.. This pointer should align with the V-groove mark at the rear of the mount, when belt tension is correct. As the belt stretches, the pointer will drift to the left of the V-groove. If the pointer is moved past the end of the V-groove, the belt needs to be replaced.
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V-Groove
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Pointer