Here is what happened: The valves hit each other. SO which ever ones hit are your problem. The only way you can tell the extent of the damage is to take the head off. Most likely you will be able to get away with just replaceing the valve(s) and a valve job. Worst case if the head of a valve got knocked off and hit the piston top then you will need a motor. Bottom line is you won't know till it's torn down.
