Found exhaust valves and seats show signs of exesive heat. allong with glazed cylinders and huge wear in rings. I haven't till now rebuilt the engine but I did clean out cooling fins and check tappet clearances. so I suspect all this wear was caused by overheating. Main problem is that when the cylinders and cylinder head fins block up with grass seed, dust, dirt, rocks and any oil leaks from the head bolts, push rod tubes. As the build up incleases the airflow past the cylinders decreases and takes the path of least resistance through the oil cooler.