opinions on the root cause of this exhaust valve failure

[The Critic]

No, replace exhaust cam, Front Rocker Arm Oil Control Valve (spool valve), timing belt kit and reassemble. If you're feeling adventurous I would also reseal the oil pump.

 

[brages]

Root cause found. The cam lobe failed. The valve was adjusted per Honda's spec but that adjustment was done on the other side of the lobe in the valve-closed position, and the cam is good in that position. In the open position the failed exhaust valve wasn't fully opening by a significant amount.

Why would an exhaust valve failing to fully open lead to a burned valve? I thought they were caused by a valve failing to fully close.

 

[JDenyer232]

Why would an exhaust valve failing to fully open lead to a burned valve? I thought they were caused by a valve failing to fully close.

I had the same question. Maybe the restricted motion allowed crud on the valve stem keeping it from closing fully?