On September 22, 2015, about 1426 eastern daylight time, an experimental amateur-built Lerch model RV6A single-engine airplane, N215DG, was substantially damaged during a forced landing near Deckerville, Michigan. The private pilot sustained minor injuries and his passenger sustained a serious injury. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 without a flight plan. Day visual meteorological conditions prevailed at the accident site. The personal flight departed Sandusky City Airport (Y83), Sandusky, Michigan, at 1345, and had the intended destination of Ray Community Airport (57D), Ray, Michigan.The pilot reported that while in cruise flight he smelled an odor and subsequently confirmed that the engine had lost oil pressure. The pilot believed that the airplane was not able to reach an airport, so he decided to shut down the engine and make a precautionary landing to a nearby dirt road. Shortly before touchdown, the pilot saw a vehicle with a trailer approaching on a crossroad and a stop sign at the road intersection. He banked the airplane to the left towards an open field to avoid the obstacles. The airplane landed hard in the field and subsequently nosed over. The airplane sustained substantial damage to the fuselage, wings, empennage, firewall and engine mounts. A postaccident examination, completed by Federal Aviation Administration (FAA) Inspectors, revealed that the lower fuselage and sides of the fuselage were covered in engine oil. Further examination established that the oil filter had separated from the adapter assembly and was hanging from the engine by safety wire. The oil filter adapter plate was observed separated from the adapter, although the adapter itself remained attached to the engine. A visual examination established that the disengaged oil-filter was the source of the loss of engine oil during the accident flight. A review of Textron Lycoming Special Service Publication No. SSP-885-1 established that the original canister-type oil filter assembly had been modified for a spin-on oil filter; however, the modification had not been completed in accordance with the installation instructions and, as such, an incorrect oil filter had been used. Although the correct heli-coil insert had been installed in the adapter, the specified converter stud was not installed. The missing converter stud was designed to engage the adapter's heli-coil and retain the oil filter adapter plate. Without the installed converter stud, the use of the specified female-threaded oil filter was not possible. As such, the use of an oil filter with a male-threaded stud had been used. A visual examination revealed that the heli-coil insert threads were damaged and pulling out of the adapter. Additionally, the oil-filter used on the accident engine, which incorporated a male-threaded stud, would have only engaged a few of the heli-coil threads. Additional examination of the heli-coil insert revealed evidence of cross-threading of the threads. A review of the engine maintenance logbook established that the incorrect oil filter adapter modification, and corresponding incorrect oil filter, had likely been used since the last engine overhaul, which was completed in September 1997. The engine, a Lycoming O-320-H2AD, serial number L-3317-76, had accumulated 627 hours since the last overhaul. The most recent oil change was completed on June 22, 2015, during the most recent condition inspection. The engine had accumulated 12 hours since the last oil change. The pilot reported that 3.4 hours after the condition inspection he noted a minor leak from the oil filter assembly. He corrected the leak by replacing the adaptor plate gasket and reinstalling the oil filter. The engine had accumulated 8.6 hours since the oil leak was mitigated.