If the timing belt breaks, the engine will stop working instantly and will not restart. On some engines, if the timing belt breaks suddenly, a major engine repair job may be in order. It is always recommended that along with timing belt replacement, you should also replace all oil seals and water pump.
If these recommendations are ignored, the old seals and the water pump may begin to leak and cause the new belt to damage prematurely. Most manufacturers recommend service between 96,000km to 120,000km
When an automotive timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized. Failure to synchronize correctly can lead to problems with valve timing, and this in turn, in extremes, can cause collision between valves and pistons in interference engines. This is not a problem unique to timing belts since the same issue exists with all other cam/crank timing methods such as gears or chains.