Causes of Failure of Timing Belts and the Solution
Running noises from belt

| Diagnosis | Solution |
|---|---|
| Tension too high: Belt whines, whistles | Adjust tension properly |
| Tension too low: Belt knocks against covering | Adjust tension properly |
Edge wear

| Diagnosis | Solution |
|---|---|
| Belt not parallel to axis: Belt runs against flanged pulley | Check drive, line up or, if necessary, replace any non-aligned pulleys, change the belt |
| Wheels axially off-centre: Timing belt cannot be properly aligned | Check drive, line up or, if necessary, replace any non-aligned pulleys, change the belt |
| Flanged pulley has flaws | Replace idler/tensioning pulleys, change the belt |
| Bearing play in components | Replace idler/tensioning pulleys, change the belt |
Fabric wear in the tooth root

| Diagnosis | Solution |
|---|---|
| Belt excessively tensioned | Change the belt, adjust tension correctly |
| Belt is overheating | Find out cause (e.g. check cold performance), take corrective action, change the belt |
| Timing belt pulley is worn out | Replace timing belt pulley, change the belt |
Unacceptable wear of tooth flanks/base separating and tooth shearing

| Diagnosis | Solution |
|---|---|
| Tension too high/too low | Change the belt, adjust tension properly |
| Trapped foreign matter | Remove foreign matter, check covering is seated properly, change the belt |
| Jammed timing belt pulley or tensioning pulley | Find out cause (e.g. defective bearing), take corrective action, change the belt |
Teeth and fabric separating from belt body

| Diagnosis | Solution |
|---|---|
| Leaks in the engine or engine compartment (e.g. escape of oil, antifreeze etc.) | Repair leak(s), change the belt |
Running marks on teeth side

| Diagnosis | Solution |
|---|---|
| Foreign matter in timing belt drive | Remove foreign matter, change the belt, check the cover is seated properly |
| Flaws in teeth of timing belt pulley caused by foreign matter or tools during fitting | Replace timing belt pulley, change the belt, ensuring it is properly fitted |
| Timing belt damaged before/during fitting | Change the belt, ensuring it is properly fitted |
Cracks on back timing belt

| Diagnosis | Solution |
|---|---|
| Ambient temperature too high/low | Find out cause (e.g. check cold performance), take corrective action, change the belt |
| Contact with foreign media | Change the belt, check the covering is seated properly |
| Back idler pulley sluggish | Replace pulley, change the belt |
| Ageing | Change the belt |
Timing belt snaps

| Diagnosis | Solution |
|---|---|
| Foreign matter in the drive | Remove foreign matter/media, change the belt |
| Contact with foreign media | Change the belt, check the covering is seated properly |
| Excessive tensioning | Change the belt, adjust tension properly |
| Belt was crimped before/during mounting | Change the belt and fit it correctly |
Defective system components

| Diagnosis | Solution |
|---|---|
| Bearing play | Replace the idler, tensioning and/or guide pulley |
| Damaged running surface | Replace the idler, tensioning and/or guide pulley |