On September 19, 2008, at 1100 eastern daylight time, a Cessna 120, N77068, incurred substantial damage during a force landing in an open field near Jesup, Georgia. Visual meteorological conditions prevailed and a flight plan was filed for the Title 14 Code of Federal Regulations Part 91, personal flight. The pilot and the passenger were not injured. The pilot stated that he planned a flight from the Macon Downtown Airport, Macon, Georgia to the Jekyll Island Airport, Jekyll Island, Georgia. They departed at about 0945. The flight went uneventful for the first hour of the estimated 2 hour flight. About an hour and twenty minutes into the flight, an opaque film began to accumulate on the windshield. Engine oil was leaking from the forward right engine cowling area. Within a minute, forward visibility was severely restricted and he had to rely on the instruments for level flight while referring out the side window for visual reference. There were no abnormal indications from the engine instrumentations. The nearest airport was too far away and the pilot elected to land in a clear field within gliding distance. The pilot approached the open field in a slip; the windshield was covered with oil. He lost visual reference as he recovered from the slip to land; estimating the flare for the touchdown. The airplane landed hard and bounced, which separated the right wheel assembly from the gear. The airplane’s right gear dug in on the second contact with the ground, resulting in the airplane coming to an abrupt stop in a nose low and tail high position. The pilot and passenger removed their four point restraint system and exited the airplane on their own. A wreckage examination a Federal Aviation Administration inspector revealed the engine oil was leaking from the front section of the engine crankcase, behind the propeller flange. Upon removal of the propeller and spinner, the forward crankshaft expansion plug was observed dislodged from it seating, allowing pressurized oil to escape from the forward end of the crankshaft. The pilot/owner stated the airplane’s engine was overhauled 39 flight hours prior to the accident.