Interference engines

Interference engines are an efficient, "free-breathing" form of engine design where the valves protrude ("interfere")into the cylinders' combustion chambers when the piston is opposite the valves. In such engines the valve timing must be correct, and the valve-timing belt or chain must be in good condition. If the belt or chain parts, the valves and pistons collide and major engine damage results. Therefore, owners of vehicles powered by interference engines should replace the timing belts or chains every 30,000 miles, though many buyers of such vehicles may not be aware of this need in their particular vehicle.