Sounds like you over-heated the engine. Valve guide moved away from the combustion chamber. Push rod laying in the engine push rod tunnel.
These are air cooled engines. You need to take the engine cover OFF every year or more, to clean the block and cooling fins. If you are scalping much or even 1 yard, you need to clean the fins. Scalping and bagging are filthy chores. This procedure is in EVERY mower engine slash small engine manual known to man. If it's air cooled pay attention.