When a V-belt fails early, most people simply fit a new one, and it fails again. The old belt is the best clue you have. Its surface, edges and cracks show what went wrong, and most causes are easy to fix once you know them.
Most early V-belt failures come from wrong tension, misalignment, worn or wrong-size pulleys, mixing old and new belts, heat, and oil contamination. Look at the failed belt: glazed sides mean slip, cracks on the underside mean bending stress or heat, a soft and swollen belt means oil, and a turned-over belt means misalignment or worn grooves.
| What you see | Most likely cause |
|---|---|
| Shiny, hard, glazed sides | Slipping: low tension or worn pulleys |
| Burn marks or a burnt patch | Belt slipped while the drive stalled or started under load |
| Cracks across the underside | Pulley too small, heat, or old age |
| Soft, swollen, sticky rubber | Oil or grease contamination |
| One side worn more than the other | Misalignment |
| Belt turned over or jumped off | Misalignment, worn grooves, loose tension or a foreign object |
| Belt sits low in the groove, groove bottom polished | Worn pulley or wrong section |
| Some belts in a set loose, others tight | Mixed old and new belts, or unmatched lengths |
| Clean break across the belt | Shock load, foreign object, or damage during fitting |
Loose belts slip and glaze; tight belts stretch and overload bearings. Use the deflection method in our V-belt tension guide and re-check new belts after run-in.
Pulleys that are offset or angled make the belt enter the groove at an angle, wearing one side and turning it over. Align with a straight edge or laser after every motor or pulley change.
Grooves wear into a dished shape, and the belt sinks, slips and wears. Check grooves with a groove gauge; if light shows between gauge and groove wall, replace the pulley.
Each section has a minimum pulley diameter. Below it, the belt bends too sharply and cracks on its underside. Check our size chart, or consider cogged belts for small pulleys.
On a multi-belt drive, new belts are shorter than stretched old ones, so they carry most of the load and fail early. Always replace the full set.
A belt that does not match the groove rides too high or too low. Match the section exactly.
Oil softens rubber and makes belts slip. Fix leaking seals and overgreased bearings near the drive, and clean pulleys with a dry cloth or a mild degreaser that leaves no residue.
Rubber ages faster when hot. Closed guards in hot sheds, belts near furnaces or kilns, and slipping belts all raise belt temperature. Use ventilated guards and stop slip at its source.
Crushers, mills and presses can stall or jam, and the belts then slip and burn. Fix the overload, use the right number of belts and consider soft starters where motors start under load.
Prying or rolling a belt over the pulley flange breaks its cords inside, even if the outside looks fine. Store spare belts in a cool, dark place, hung on wide pegs, away from sunlight, ozone sources such as motors, and oil.
A squeal at start-up usually means tension is too low for the starting load. A constant squeal can also mean worn grooves, oil on the belt, misalignment or an overloaded drive. Do not use belt dressing to silence it; find the cause.
Write down the date, drive, section, how long the belt lasted and what it looked like. Patterns appear quickly: one drive eating belts every month usually has a pulley, alignment or guarding problem, not a belt problem.
Why do my V-belts keep breaking?Common causes are shock loads, mixing old and new belts, misalignment, worn pulleys and damage during fitting. Read the failed belt for clues.
Why do V-belts crack on the underside?Usually bending stress from pulleys smaller than the minimum diameter, heat or old age.
What causes a V-belt to turn over in the groove?Misalignment, worn grooves, low tension or a foreign object in the groove.
Should I replace all belts on a drive if only one fails?Yes. New and used belts differ in length, so the new belt would carry most of the load and fail early.
Belts failing too often? WhatsApp us photos of the failed belts and the drive, with section and size, and our team will help find the cause.