Broken rocker

[Lonestar10]

730k km soo around 500k miles... last overhead was done when? and did you do it so you know it was set right? most shops arent even capable of putting a lugnut cover on right.

im not sure you have to pull the head off maybe replace the rocker and bar the engine over a few times and check for interference and watch that valve to make sure its moving up and down properly.

roughly what rpm were you running when this happened and were you into a full accell or an engine braking at that RPM which is where the most stress on things would be

maybe even find someone with some timing wedges to make sure your cams havent slipped out of time.

exhaust valves get the hottest and grow the most if the overhead wasnt right and was to tight that could be the issue. for every 100 degrees on a peice of metal it grows about 1/1000 of an inch and that can cause issues if a .027 set it done but the valve grows .010 at full throttle and the valve has wore into the head .017 theres a recipe for disaster.