I have a briggs and stratton 20 hp I/C engine in my mower. It starts and runs fine but if I turn it off after running it for 30-45 minutes it will not start again until I let it cool off for 30+ minutes. It gets hot enough to burn the oil deposits on the crankcase. What are the causes of this type engine overheating?

Need to pull the blower housing off and see if the head fins are packed with dirt and debri.
Could be valves
Could give better info if there was a model # posted.
Luck

Low oil level, dirt in air fins (have to remove the shrouds around the cylinders to get at fully) Dirty old oil, be sure to do oil change, and replace the oil filter if this engine has it.