Belt tensioner failure signs

Belt tensioners are extremely important in the proper operation of the accessory belt drive system. A tensioner maintains the correct amount of tension on the belt at all times throughout its duty cycle. It also helps protect other components such as the alternator and water pump from undue stress and premature failure. In addition, a tensioner is a relatively inexpensive part to replace. So, every time you replace a multi-ribbed belt, be sure to replace the tensioner at the same time.

Furthermore, when a tensioner has reached the end of its service life Gates recommends that all wear parts are replaced at the same time to ensure the best long-term solution.

The importance of correct belt tension

If the belt tension is too low, the belt will slip causing noise, extremely high temperatures and premature belt wear, all of which can lead to the poor functioning of the belt-driven accessories. If the tension is too high, this will cause excessive wear to the belt-driven accessories.

HOW TO DETECT A BELT TENSIONER THAT IS NEAR FAILURE?

The following signs indicate that a tensioner needs to be replaced:
Problem_Diagnosis_361x323_Tensioner_Rust

1. Rust bleed and cracks

Appearance: Rust is bleeding between arm and base or dripping from the tensioner. Also, check the tensioner for cracks or damage to arm, housing and bracket. Some damage can’t be seen unless the tensioner has been removed.

Cause: Rust bleeding or dripping is a sign of internal component wear. Most common crack damage occurs at tensioner “stops” and mounting bolts.

Solution: Replace the tensioner.

Problem_Diagnosis_361x323_Tensioner_Pulley_Bearing_Wear

2. Pulley bearing wear

Appearance: With the engine off and the belt removed, manually rotate the pulley. If you notice noise, resistance or roughness, the problem is likely to be pulley bearing wear.

Cause: Defective bearing and/or pulley.

Solution: Replace the complete tensioner. Do not attempt to replace a worn pulley in a used tensioner assembly but always replace the entire tensioner assembly, as part failure will inevitably follow quickly.

Problem_Diagnosis_361x323_Tensioner_Pulley_Wear

3. Pulley wear

Pulleys are made from plastic, nylon or steel and have either a flat or grooved surface.

Appearance: Flat surfaces should be smooth and free from chips, cracks and dents. Grooved surfaces should be free of chips, cracks, dents and embedded debris within the grooves. The high points of the grooves should not be worn down and be of equal height. Plastic pulleys have fins in sidewalls that should not be cracked or broken.

Cause: Belt wearing into the pulley.

Solution: Replace the complete tensioner. Do not attempt to replace a worn pulley in a used tensioner assembly but always replace the entire tensioner assembly, as part failure will inevitably follow quickly.

Problem_Diagnosis_361x323_Tensioner_Assembly_Misalignment

4. Tensioner assembly misalignment

Appearance: Abnormal belt tracking on tensioner pulley.

Cause: Bent or misaligned mounting bracket, improper tensioner installation or corrosion/contamination between tensioner base and mounting surface.

Solution: Misalignment is easy to diagnose thanks to Gates DriveAlign® laser alignment tool. If misalignment persists, replace the tensioner.
Problem_Diagnosis_361x323_Tensioner_Noise

5. Tensioner noise

Appearance: Squeaks and rattles coming from the tensioner.

Cause: Failure of bearings or pivot area will cause excessive noise.

Solution: Replace the tensioner. Also read our guidelines to correctly diagnose accessory belt drive noise.

Problem_Diagnosis_361x323_Tensioner_Arm_Misalignment

6. Tensioner arm misalignment

Appearance: Abnormal belt tracking on tensioner pulley. Shiny, smooth streaks or gouges in tensioner housing or arm.

Cause: Metal-to-metal contact between arm and spring housing.

Solution: If tensioner arm misalignment is apparent, the pivot bushing has worn down and the tensioner should be replaced.

Problem_Diagnosis_361x323_Tensioner_Arm_Oscillation

7. Excessive tensioner arm oscillation

Appearance: Back and forth sway of tensioner arm during operation.

Cause: If large swings occur or continual oscillation is evident, the damping system or spring torque has most likely failed. Another possible cause can be torsional vibration damper or overrunning alternator pulley failure.

Solution: If excessive oscillation is observed, replace the tensioner. Pay particular attention to the condition of the torsional vibration damper and overrunning alternator pulley.

Problem_Diagnosis_361x323_Tensioner_Grinding_Arm

8. Binding or grinding tensioner arm movement

Appearance: Cycle the tensioner (mounted on the engine) through the entire range of motion (from stop to stop) by applying torque to the arm with a wrench. The tensioner arm should move smoothly and freely.

Solution: If you notice a binding, sticking or grinding tensioner arm, the tensioner should be replaced.

Note: The positioning of the wrench depends on the tensioner type (tensioner end, tensioner hole...). Simply position it in the same way as to install the tensioner.

Problem_Diagnosis_361x323_Tensioner_Loss_Spring_Force

9. Loss of spring force

Appearance: Move the tensioner arm (tensioner being mounted on the engine) through its entire range of motion with a wrench. There should be resistance to this movement. If there is none, the spring has lost its force. Other indicators are belt squeal from slippage, or loss of rotation of a belt-driven component.

Solution: If any of these are present, replace the tensioner.

Note: The positioning of the wrench depends on the tensioner type (tensioner end, tensioner hole...). Simply position it in the same way as to install the tensioner.

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