Exhaust Valve
An engine valve that opens to allow spent combustion gases to escape from the cylinder into the exhaust manifold.
The exhaust valve is a critical valvetrain component located in the cylinder head that manages the removal of spent gases from the combustion chamber. Like the intake valve, it is kept tightly closed by a strong valve spring to maintain cylinder compression during the compression and power strokes. During the exhaust stroke, the camshaft pushes the exhaust valve open, allowing the piston to sweep the hot combustion byproducts out of the cylinder and into the exhaust manifold.
Exhaust valves operate under extreme thermal conditions, exposed to superheated exhaust gases exceeding 1,200 degrees Fahrenheit as they exit the chamber. To withstand this intense heat without melting or warping, exhaust valves are manufactured from specialized heat-resistant steel alloys, and some heavy-duty valves are filled with liquid sodium to help transfer heat away from the valve face to the valve guide and cylinder head cooling jackets.
If an exhaust valve does not seat properly, hot combustion gases can blow past the seal, causing the valve to overheat and burn out (a "burnt valve"). Burnt or bent exhaust valves lead to a permanent loss of compression in that cylinder, resulting in a persistent engine misfire, rough running, and loss of power. Resolving this issue requires cylinder head removal and replacement of the damaged valves.