On November 19, 2000, about 1200 Pacific standard time, a Collette Glassair III, N540AK, nosed over about 13 miles west of Guistine, California, during a forced landing after the pilot encountered smoke in the cockpit. The private pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The pilot, the sole occupant, sustained serious injuries; the airplane sustained substantial damage. The personal flight departed Guistine about 1135 en route to the Reid-Hillview Airport in San Jose, California. Visual meteorological conditions prevailed and no flight plan had been filed. The accident site was an abandoned grass strip at 31 degrees 13.73 minutes north latitude and 121 degrees 22.45 minutes west longitude. The pilot and a friend in another airplane departed Reid-Hillview earlier in the morning and flew to Guistine. The pilot stated they refueled at Guistine and the friend was the first to depart. The accident pilot said that oil was spewing onto his windshield, he was losing oil pressure, and smoke was filling the cockpit. He made an emergency landing on an abandoned dirt strip that was about 1,400 feet long. However, the airplane overran the runway into a ravine and overturned. The witness reversed course and saw smoke in the distance, but could not keep sight of the airplane all the way to the ground because of haze. The pilot said a mechanic completed maintenance the day before the accident, which included an oil change and replacement of the crankshaft nose seal. A post maintenance run-up revealed no oil leaks. A representative from Textron Lycoming examined the engine under the supervision of the Federal Aviation Administration and submitted a written report. The engine sustained no visible damage resulting from the forced landing. Visual examination revealed no evidence of catastrophic mechanical malfunction or fire. He observed a significant amount of engine oil emanating from the nose cowling where the engine and propeller flange protruded. The oil film proceeded aft onto the windscreen as well as the horizontal and vertical stabilizers. The Lycoming representative examined the spark plugs. He did not observe any mechanical damage, and their color indicated normal operation according to the Champion Spark Plugs Check-A-Plug chart AV-27. He examined the cylinders' combustion chambers with a lighted borescope. The cylinder walls, valves, and pistons exhibited no mechanical damage. Oil lines within the engine compartment were secure on their fittings. The propeller governor was secure and not leaking. The oil filter and oil filter converter plate were properly installed and secure. There were no visible contaminates in the oil filter or suction screen. The crankshaft oil seal was out of its bore and resting on the crankshaft. The Lycoming investigator removed the propeller, but did not observe evidence of oil leakage at the propeller seal. Further investigation was terminated until the owner disassembled the engine to comply with a sudden stoppage inspection. The owner had the engine overhauled. He reported that one oil ring was cracked, but no compression rings were broken. There was evidence of overheating from running lean. He discovered that the breather hose had been mounted over the motor mount rather than under it. In this location the hose was pinched when the cowling was installed. The owner said this plugged the breather hose and pressurized the case. He thought this pressure would force the oil out through the front seal.