• Because of their constant heat exposure, exhaust valves are some of the most likely to be burnt in vehicles. This can cause both serious and annoying problems. If you suspect that your exhaust valve has been burnt, you should get it replaced or replace it yourself as soon as possible.

    Burnt Valve Diagnosis

    Most people first suspect a burnt exhaust valve because their engine starts to backfire, or make associated popping or guttural noises that are more connected with exhaust than with direct engine operation. One of the most accurate ways to confirm a burnt valve, or at least a valve problem, is to perform a compression test. A faulty exhaust valve will affect compression most of all. A more immediate test may be possible if you want to wait for your engine to cool before starting it again and putting your hand on the exhaust pipe while it is cool. If there are any signs of suction, you may have a burnt exhaust pipe. The most direct way to notice a burnt exhaust valve is by looking at the valve as it is on the engine. You will be able to tell if the valve has lost a chunk of metal toward the head. A problem valve will also generally be the same color as the metal around it, while a working valve should be colored by sediment or ash (caused because of the channeled heat). Burnt exhaust valves also often have a ragged or warped look, instead of being perfectly circular, which is one of their primary problems.

    Burnt Valve Causes

    Exhaust valves run very hot, at around 1,200 degrees Fahrenheit when the engine is operating normally. In order to withstand this intense heat, the valves are made out of strong alloys; however, no metal can withstand those temperatures for long periods of time without losing shape, so exhaust valves also transfer heat. Exhaust valves maintain constant contact with the valve seat, which allows them to "drain" about three quarters of the heat the valves receive. The rest of the heat is passed along through the pipes and dissipated. However, if the valves cannot pass most of the heat off through the seat, or if there is an unwanted heat spot created in the valve or head, then the valve can become burnt. This can be caused by deposits built up by the constant heat, or by weak springs or improperly fitted valves that do not allow for sufficient contact between the valve and the seat. Replacing the valve will only create a temporary fix to this problem, and the causes behind the uneven heat distribution need to be solved first in order to preserve the integrity of the new valve.



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