Amateur-built RV-7A N5025G accident near Gerrardstown, West Virginia

Probable cause

The pilot/builder's misjudgment of the required spacer width needed after engine housing lap grinding, which resulted in bearing oil hole misalignment and insufficient internal engine lubrication.

NTSB analysis

According to the pilot, after about 2 1/2 hours of local flight, while maneuvering at 3,000 feet, the airplane's rotary engine coolant temperature rose. As the pilot turned the airplane back toward the departure airport, the engine seized and would not turn over during an attempted restart. The pilot performed a forced landing in a field, and the airplane nosed over. The pilot, who was also the airplane's builder, subsequently disassembled the engine and found that the stationary gear/bearing was frozen to the eccentric shaft. The pilot also reported that he had recently attempted to fine tune the engine by having the side and intermediate housings undergo lap grinding. The pilot knew the grinding would require wider spacers, which he used, but which may have still been insufficient in width. The insufficient width resulted in bearing oil hole misalignment on the eccentric shaft, which blocked oil from reaching the rotating engine and reduction drive shaft parts.

Text from the NTSB. Open the NTSB docket for ERA12LA293 for the full record.