As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROTARY VALVE GEAR OIL SUMP FASTENER BROKE AND SUMP FELL TO A LOWER LEVEL THAN THE CRANKSHAFT. LACK OF LUBRICATION FROM SUMP CAUSED BRASS ROTARY VALVE GEAR TO SHEAR OFF ITS TEETH. RESULT WAS THE ROTARY VALVE SLIPPED AND BECAME OUT OF TIME WITH ENGINE; THUS, ROUGHNESS AND POWER LOSS OCCURRED.