I woke up this morning, hopped in the Scout, and headed to the Waffle House to get my day going. On the way down the mountain, I noticed that there was a “chirp” coming from the engine compartment. It was a new noise, and if you have a Scout II. A new noise is not NEVER a welcome one. I decided to do a little research to see if I had a “real” problem or maybe something I could handle.
The Real Reason Belts Squeal, Chirp, and Make Other Noise
If a newly installed serpentine belt is making noise, it is a sign of a problem within the engine’s front-end drive system. Serpentine belt noise is the equivalent of a “check engine” light that indicates something is wrong with the belt drive system. But surprisingly, more often than not, the belt is not the culprit.
Squeals and Chirps: The Most Common Serpentine Belt Noises
There are two types of noise that a serpentine belt typically makes. One is the chirp, the other is the squeal. They each are the result of different issues within the front-end drive system.
Serpentine Belt Chirp
The chirp makes a series of sharp, intermittent, “rhythmic” sounds. As the belt speed increases, the pitch and volume stay constant, hence why you hear a continued belt chirp when accelerating.
Six Reasons for the Chirp
- Pulley misalignment is the #1 cause of noise
- Improper installation
- Worn belt ribs
- Worn pulley bearings, which cause wobble or excessive free-rock
- Contamination from oil, power steering fluid, antifreeze or belt dressing
- A low-quality belt was installed
Solutions for the Misalignment Chirp
- Check the alignment of all pulleys, either with a straight edge or a laser alignment tool.
- Ensure all accessory pulleys and brackets are tightened snug to their mounting surfaces.
- Inspect and replace all accessories and pulleys that are difficult to rotate due to rough or seized bearings, or show excessive wobble or free-rock. Keep in mind that power steering pulleys and worn harmonic balancers can also cause misalignment.
Serpentine Belt Squeal
A squeal is high-pitched, lasts several seconds, and may change in volume but not in pitch.
Top Three Reasons for the Squeal
- Low belt tension is either caused by low installation tension, a stretched belt, extreme belt wear, tension spring degradation or a belt that’s too long.
- High accessory/idler pulley drag from seized bearings or accessory failure/lock-up.
- Fluid contamination on the belt caused by exposure to belt dressing, oil, antifreeze or another chemical.
Solutions for the Tension Squeal
- Manual tensioned applications should be checked for proper tension (35 lbs. per rib) and then re-tensioned after 5 minutes of run-in (30 lbs. per rib). This allows the belt to seat in the pulleys.
- On vehicles with automatic belt tensioners, the tensioner pulley should turn freely without binding and the tensioner arm should move smoothly through its entire range of motion with adequate tension.
- Always check the tensioner bearing for noise and wear. Replace any tensioner where the bearing feels rough or the pulley has run-out.
- While the belt is removed, inspect all accessory pulleys and idlers to ensure free and smooth rotation. If there is binding or rough rotation due to a dry bearing, then the pulley and/or accessory should be replaced.
- If the belt is contaminated with motor oil, power steering fluid, antifreeze or any other petroleum-based lubricants, it will weaken and even cause the EPDM belt to swell and create noise. Any serpentine belt that has been oil soaked must be replaced.
- NEVER try to solve issues with belt dressing.
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