Looking to define the reason(s) exhaust valves fail. reading the LOP thread, there is a lot of generalization about operations - such as  damage the engine internal pressure - high ICP burn up your engine detonation there are continual reports of top end replacements at 1000 hours or less, yet some operators can go to TBO without issues.  How can we define these differences that make sense relating to exhaust valve failures. Mechanical issues are well documente