DURING FLIGHT, THE ENGINE RPM EXCEEDED ITS MAXIMUM LIMIT. THE PILOT ATTEMPTED TO REDUCE THE RPM BY USING THE PROPELLER CONTROL, BUT THIS HAD NO EFFECT. THE PILOT WAS IN THE PROCESS OF SHUTTING DOWN THE ENGINE WHEN ENGINE OIL SPRAYED OUT THE COWLING AND ONTO THE WINDSHIELD. UNABLE TO GLIDE TO AN AIRPORT, HE ELECTED TO LAND IN A CORN FIELD. AS HE APPROACHED THE FIELD, HE SAW POWERLINES IN HIS GLIDE PATH, THEN LANDED HARD WITH THE GEAR RETRACTED AFTER MANEUVERING TO AVOID THE LINES. A TEARDOWN OF THE ENGINE REVEALED THAT THE NO. 3 CYLINDER EXHAUST VALVE GUIDE WAS WORN WELL BEYOND ITS SERVICE LIMIT AND ALLOWED EXCESSIVE BLOWBY FROM THE CRANKCASE. THE OIL SUPPLY HAD BEEN DEPLETED AND THERE WAS DETERIORATION OF METAL TO METAL PARTS DUE TO LOSS OF LUBRICATION. THE VALVE GUIDE, PN 631496, HAD BEEN OUT OF PRODUCTION FOR ABOUT 8 OR 9 YEARS.