Download Common causes of camshaft timing belt failure on the above vehicles are due to incorrect operating tension, or ingress of dirt, water, or debris entering the timing belt cover. Predominantly on Fiesta models a high percentage of camshaft timing belt failures occur after the ancillary poly ‘V’ drive belt has failed, where strands of material off the broken belt have entered the timing belt cover. This is especially so where an ancillary belt has been fitted that does not contain “Kevlar” based materials. It is therefore important to always remove the timing belt cover to check for belt debris if the ancillary belt has failed. Any contamination that enters the timing belt cover can become compressed between the surfaces of the camshaft timing belt and drive pulleys. This causes wear to both the belt teeth, backing surface, and damage to the drive pulleys, resulting in premature failure of the camshaft timing belt. Later engines have modifications to improve the sealing of the belt cover around the crankshaft pulley, to reduce the level of outside contamination.