There are two types of engines that use timing belts. They are described as: "Interference Engines" and "Non-interference Engines"The difference lies in the proximity between the valves and the pistons. On an interference engine, if the timing belt slips even one notch, the piston can crash into an open valve causing serious engine damage by bending valves and breaking pistons. Non-interference engines will usually not self-destruct, but in either case if the belt fails, the engine will immediately shut down leaving you stranded.