As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MOMENTARY SEVERE VIBRATION, POWER LOSS AND ENGINE RPM DROP OCCURRED IN-FLIGHT THEN RETURNED TO NORMAL. COMPRESSION CHECK (COLD) REVEALED STUCK INTAKE VALVE ON NR 6 CYL. INTAKE VALVE GUIDE ID MEASURED .4035" (UNDERSIZED). LIMITS .4040 / .4050. NO BUILDUP FOUND ON VALVE GUIDE OR STEM. VALVE GUIDE REAMED TO PROPER SIZE PER LYC. TABLE OF LIMITS SSP1776. NO REOCCURRENCE REPORTED.