Did a 2-3-2 shift this morning and it instantly started misfiring. Pulled the valve cover off to find #3 exhaust rocker snapped in half, and #3 intake rocker out. I put a spare pair of rockers in and it drove fine for a little while, I shut it off and it sat for about 4 hours. When I restarted it the engine ran great for about 30 seconds then started missfiring. Pulled valve cover again to ring #3 exhaust valve stuck open and rocker out. Popped valve closed with a screwdriver and reinstalled rocker, it lasted another 30 seconds then snapped the rocker again.
Cylinder head coming off Saturday but any guesses as to what happened?
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