As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT EXPERIENCED PARTIAL POWER LOSS. LANDED WITHOUT INCIDENT. INSPECTED ENGINE NOTED HOLE, NR 3 SPARK PLUG WITH A LARGE CRACK EXTENDING DOWN TO EXHAUST PORT FLANGE. FURTHER INSPECTION ALSO FOUND NR 1 CYLINDER CRACKED AT SAME LOCATION BUT HAD NOT YET HAD COMPLETE FAILURE. POSSIBLE CAUSE MAY BE IMPROPER LEANING PROCEDURES. NOT: AIRCRAFT USED EXTENSIVELY FOR FLIGHT TRAINING. (K)