Burnt valve is caused by combustion gases escaping between the valve and valve seat when they are not sealing correctly. The hot combustion gases are forced past the valve which starts to burn away the edge of the valve, progressively getting worse the longer it is left without being rectified. Normally this type of failure affects the exhaust valves only, but it can also damage the intake valves.
This picture shows how Incorrect valve clearance can jeopardize the valve sealing and burnt the valve.
R25 Burnt valve
When Valve is burnt as the picture above, engine compression will lower and affects performance. So how to detect it? easy. We do compression test first!.
In the next entry, We will discuss how we can prevent it. Insyallah.
regards,
PG