The valve train of the Zetec and Endura-Turbodiesel engines is driven by a toothed belt. It rotates on pulleys outside the crankcase. Toothed belts are not subject to maintenance, they are made of synthetic material with steel wire inserts and are tensioned by a hydraulic tensioner. Ford recommends replacing the belt after a maximum of 150,000 km. Since replacement can distort the valve timing of the engine, it is better to entrust this work to a Ford dealer. If necessary, he will also immediately check the tensioner and, if necessary, replace it.
The hydraulic timing belt tensioner in Ford OHC/DOHC engines lasts longer than the timing belt. However, you should check the device no later than 150,000 km and replace it if there are slight traces of sweat on the housing.