Your car's engine is not a self-contained unit. It needs fuel and air to function properly. In order to let these substances in and out of the engine, there are a number of valves throughout the engine that rely on the camshaft to open and close them. General upkeep can prevent problems from forming in the valves, but you should know the warning signs of valve failure as well.
Valves may break, burn, wear down or become loose - all of which can lead to complete failure. Periodically examine valves for signs of damage. Keep an eye on the amount of wear, as a little bit is not harmful, but once the valves are worn enough they may begin to present problems. You should not only inspect the valves, but the entire valve train to find and replace any worn or damaged parts.
In some cases, damage is caused by defective valves. Installing a valve requires precision and attention to detail. If there is even a slight variation in the actual valve from the specifications indicated in the owner's manual, it may lead your valves to fail. Prior to installation, you should also inspect every valve for any signs of defects that could create problems down the line. This is the second leading cause of valve failures behind thermal and mechanical overstress, according to AA1car.com.
In some cases, a burned valve can cause compression problems in the engine, which will affect the motor's performance. Exhaust valves are far more prone to burning, as the gases being pulled from the combustion chamber are hot (upwards of 1300 degrees Farenheit), whereas the air being brought in by the intake valves is much cooler. The valve seat is designed to remove some of the heat and dissipate it by way of the valve stem. If anything inhibits this process, the valve can burn and will need to be replaced. Burning may also occur if the fuel mixture being burned in the combustion chambers causes misfires. This creates hotter than normal temperatures that will damage the valves and other engine parts.
Valves can also break, and this typically occurs on either end of the valve stem. Sudden temperature changes and rough use can weaken the connection between the valve and the stem or the other end of the stem and cause it to break. When this happens, you should also check the rocker arm, as it may be damaged or misaligned. Bent or worn stems may also be the source of the problem.
If you suspect the valves are not acting properly, you may want to check the timing belt and the camshaft. The camshaft is responsible for opening and closing the valves at the correct intervals, and the timing belt or chain keeps the camshaft running smoothly. You should also keep an eye on the valve seals. These rubber O-rings, positive seals and umbrella seals are in place to control how much oil reaches the valve guides. If they are insufficiently lubricated, it could affect the timing of the valve opening, which would in turn affect engine performance and threaten the health of the valves and other engine components.
Since valve replacements are extremely precise, it is best to leave the actual replacement to a professional, unless you are a seasoned mechanic or a gearhead who likes a challenge. However, even if you are not planning to fix the problem yourself, it is always best to be aware of what can go wrong in your engine and how it may happen to catch problems early.