- hardened rubber on the outside of the belt. If the outer side of the belt is shiny, inelastic, and so hard that it does not leave marks when pressed hard with a fingernail (pic. 3.6a);
- 2 cracks in the rubber on the outside of the belt (pic. 3.6b);
- cracks 3 or exfoliated material;
- cracks 4 at the root of the tooth;
- 5 cracks on the sides of the belt.
Pic. 3.6a. Hardened rubber on the outside of the belt | 
Pic. 3.66. Timing belt defects: 2 - Cracks in the rubber on the outside of the belt; 3 - Cracks or delamination of material; 4 - Cracks at the root of the tooth; 5 - Cracks on the sides of the belt |