On April 15, 2015, at 1600 central daylight time, a Robinson R44II helicopter, N754R, rolled over during an off-airport precautionary landing in Dunlap, Illinois. The commercial pilot and passenger were not injured. The helicopter was substantially damaged. The helicopter was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as an aerial observation flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated at 1500, from the Greater Kankakee Airport (IKK), Kankakee, Illinois.The pilot stated they were observing and counting geese at an altitude of 300 feet above the ground at an indicated airspeed of 60 knots immediately before the accident. He stated he increased the collective to transition to another area when he noticed an increase in engine rpm and a decrease in rotor rpm along with a main rotor warning light. The clutch warning light did not illuminate. The pilot initiated a downwind autorotation to a plowed field. The pilot stated that due to the tailwind and forward speed, the helicopter tipped forward on its skids, the main rotor contacted the ground and the helicopter rolled over. A postaccident examination of the wreckage by a Federal Aviation Administration inspector revealed oil inside the clutch shaft at the tail rotor end of the shaft. The inspector stated there was a roughness when he rotated the sheave and there was oil residue on the forward side of the sheave. He stated they flushed small particles of magnetic chips from the sheave bearings and there was no damage to the bearing races. The clutch, V-belts, and the belt tension actuator were subsequently removed for inspection at Robinson Helicopters under NTSB supervision. The examination of the clutch revealed an excessive amount of oil was on the forward face of the sheave and around the aft yoke. The actuator support bearing rotated smoothly. A slight roughness was noted when rotating the sheave on the shaft. The bearings were flushed with solvent. Three small metallic flakes were caught in a filter. Both bearings rotated smoother, but still had areas of roughness. The sheave grooves appeared to have normal wear. Oil drained from the clutch appeared to be the correct amount with very small metallic flakes in the oil. The oil was dark, but did not smell burnt. The clutch was disassembled and a small amount of oil was observed between the aft plug and the aft yoke indicating that the plug had been leaking. Visual inspection of the sprag did not show any anomalies. The four V-belts showed wear that was consistent with the reported time in service. The belt tension actuator was bent during the accident impact. The screw tube and the left-side stack of springs were bent. The heat shrink material on both spring switches was red and blue. According to the manufacturer, black heat shrink was used at the factory. The actuator down limit screw was extended about 0.4 inch and the extension was measured as 1.3 inch. The typical extension range is 0.08 inch to 1.1 inch. The actuator was placed on a test stand and the actuator functioned normally. Although there were minor anomalies noted during the examination of the clutch, V-belts, or belt tension actuator, none of the anomalies would have prevented the normal operation of the clutch system.