Some of the more common symptoms of a worn-out or broken engine exhaust valve are rough idling, backfiring, reduced power and decreased gas mileage. In certain cases, this problem can even lead to total engine failure, so it is important to have it looked at by a mechanic immediately.
Outright valve failure can lead to a number of serious issues and cause a chain reaction of damaging events. In most cases, the problem begins with a broken or burnt-out valve. Burnt valves are caused by an improper seal between the valve and valve seat, which allows some of the extremely hot combustion gas to escape around the valve. As the gas passes around the valve, it begins to burn the edges of the valve due to the extreme temperatures.
When the engine exhaust valve becomes stuck open, it can not only lead to the valve burning, but may also cause the valve to become broken if it gets hit by the piston. Valve breakage and burning are the two most common causes of valve failure. In addition, the valves may also become bent by a collision between the valve and piston. The valve stem may also become worn-out on higher mileage vehicles.