A V-belt telling you something is wrong through noise, heat or premature wear is the system telling you something is wrong. The belt is rarely the root cause, it is the victim. This troubleshooting guide helps you find the actual problem so the replacement belt does not fail the same way.
Problem 1, Squealing / Chirping Noise
Symptoms: High-pitched squeal on startup or under load. Sometimes intermittent.
Causes:
- Under-tensioned belt, most common cause
- Oil or water on belt or pulley surface
- Pulley groove wear, belt bottoming out
- Belt too small for the cross-section requirement
Fix: Check tension first. If correct, inspect groove profile. Clean pulley surfaces with dry cloth. Never use belt dressing spray, it accelerates deterioration. Replace belt if glazed.
Problem 2, Belt Slipping Under Load
Symptoms: Driven machine runs slow; motor running hot; burning smell.
Causes:
- Insufficient tension
- Worn pulley grooves, insufficient wedging action
- Wrong belt cross-section for the power requirement
- Belt glazed from previous slipping episodes
Fix: Re-tension. If slipping continues, check grooves with gauge. Check design power against belt rating. A glazed belt cannot be recovered, replace it.
Problem 3, Belt Cracking on Outer Cover
Symptoms: Fine transverse cracks visible on the flat outer face of the belt.
Causes:
- Normal aging in hot environments (common in South India)
- Storage near heat sources or ozone-generating equipment (motors, welders)
- Belt operating in temperatures above 60°C continuous
Fix: Surface cracks that do not penetrate to the cords are cosmetic, monitor but not urgent. Deep cracks exposing cord: replace immediately. Improve storage conditions for spare belts.
Problem 4, Cracking on Inner (Groove) Face
Symptoms: Cracks between the cogs on the inner face. More serious than outer surface cracking.
Causes:
- Belt running over pulleys smaller than minimum recommended diameter
- Belt operating in cold temperatures (below 0°C)
- Idler on the inside of the belt (increases bending stress)
Fix: Replace belt. Check small pulley diameter against minimum for the cross-section. If space is tight, switch to cogged belt (AX/BX/CX) which handles smaller pulleys.
Problem 5, Edge Wear / Uneven Wear Across Width
Symptoms: One edge of the belt worn more than the other. Fraying visible.
Causes:
- Angular or lateral misalignment between pulleys
- Pulley groove not correctly profiled for the belt section
- Worn or damaged pulley flange
Fix: Correct alignment with straightedge or laser tool. Check groove profile. Replace damaged pulleys.
Problem 6, Belt Jumps / Comes Off Pulley
Symptoms: Belt dislodges from grooves during operation, especially on startup.
Causes:
- Excessive misalignment
- Under-tensioned belt in a short-centre drive
- Severe shock loading (compressor, stone crusher)
- Belt too long for the centre distance
Fix: Check and correct alignment. Verify belt length designation is correct. Increase tension. If shock loading: consider adding an idler or switch to cogged or narrow wedge belt.
Problem 7, Uneven Tension / Whipping (Multi-Belt Drive)
Symptoms: In a multi-belt drive, some belts are slack while others are tight. Belts whip and vibrate.
Causes:
- Belts are not a matched set, different lengths
- One belt replaced without changing the full set
- Belts from different manufacturers mixed
Fix: Replace the entire set with new matched belts. JK Fenner supplies matched sets with ±0.5% length tolerance.
Quick Reference, Problem to Cause Matrix
| Symptom | Most Likely Cause | First Check |
|---|---|---|
| Squeal on start | Under-tension | Deflection tension check |
| Burning smell | Slip / over-tension on bearing | Belt temp + bearing temp |
| Edge fraying | Misalignment | Straightedge alignment check |
| Inner face cracks | Small pulley / cold | Small pulley diameter vs spec |
| Short belt life (<6 months) | Wrong selection | Re-calculate design power |
| Belt runs off pulley | Misalignment / wrong length | Alignment + belt designation |