Valve Spring : The valve spring uses hundreds of pounds of force to close the valves within the engine’s cylinder head. A valve spring usually never has a problem, however they can break or weaken. If there is a problem with a valve spring, the engine may not run properly, misfire or damage to the valve may occur. Valve springs should be measured when the cylinder head is being rebuilt. Some valve springs can be replaced in the vehicle while other’s bust have the cylinder head removed to replace them.