An exhaust valve is a valve on a cylinder in the internal combustion engine. This is the valve that opens up and releases burned fuel into the exhaust manifold. The exhaust valve is mechanical and sometimes is referred to as a ‘poppet valve’. An intake valve can also be called a poppet valve. The exhaust valve has a stem attached to the back of the valve head that pushes the valve head so that it opens and closes on the cylinder.
On an internal combustion engine there is a piston that travels up and down in each cylinder when the engine is in operation. This action basically involves four strokes which are the intake, compression, power and exhaust strokes. When the piston travels down the cylinder it is called the intake stroke. The piston travels up on the compression stroke and down again on the power stroke. The fourth stroke is the exhaust stroke when the piston is at the bottom of the cylinder. When the piston is at the bottom of the cylinder the exhaust valve opens up so that the burned gas can escape into the exhaust manifold as the piston travels back up to the top of the cylinder pushing it all out. Then the exhaust valve closes again. This process is repeated over and over again as long as the engine is running.
When the exhaust valve opens and allows the exhaust gas to be pushed out into the exhaust manifold it will continue to exit out the pipe and muffler. The exhaust valve is usually made of metal and shaped like a flat disk that has a valve stem on one end. A spring connected to the cam pushes the valve stem that is connected to the valve head.
When the exhaust valve is not operating correctly it can cause problems. For instance, backpressure caused by a bad exhaust valve during the exhaust stroke can cause the engine to loose power. This sometimes happens when the exhaust valve does not operate efficiently and causes resistance to the piston when it pushes against to get the exhaust gas out. One remedy for this is to have two exhaust valves so that the exhaust gas has a larger avenue of escape. When there is not enough engine power it can decrease fuel efficiency.
The location of an exhaust valve on the internal combustion engine can vary. Usually the valve is located on top of the cylinder opposite of the intake valve. However, on some engines the exhaust valve and in the intake valve can be located on the sides of the cylinder. Still yet, you can find on some engines that the intake and exhaust cylinder can be located one on top and one on the side. Sometimes the engine will be fitted with an exhaust header. The exhaust header is like a small exhaust pipe for the cylinders and will collect the spent gas and fuel and can help to eliminate back pressure problems. An exhaust header can give more power to the engine because it can pull the exhaust valve to suck the exhaust out easier. This causes the cylinder to work easier because it eliminates pressure when the exhaust is being pushed out. Many performance vehicles have an exhaust header installed on the engine.
Sometimes the exhaust valve or the seal around the exhaust valve will have to be replaced. You can find a replacement online or in various auto parts stores. You can replace exhaust valves yourself or take your vehicle to a qualified mechanic who you trust with your engine repairs for replacement.