What was found
CRUISE FLIGHT FL 240, 25 HRS SINCE NEW CHAMPION IGNITION HARNESS, BLUE LABEL TCM/CAT BENDIX S6LN-1205 MAGNETO, AND CHAMPION RHB32E SPARK PLUGS AT ENGINE OVERHAUL (25 HRS TTSMOH OF ENGINE). IN CRUISE FLIGHT LOST 5 INCHES OF MP PRESSURE ON NEWLY OVERHAULED RH ENGINE. IN FLIGHT TROUBLE SHOOTING REVEALED MARKED ENGINE ROUGHNESS WHEN OPERATING ONLY ON RH MAG. POST FLIGHT INSPECTION REVEALED EVIDENCE OF ARCHING ON BOTTOM CYLINDER #2 IGNITION LEAD AT THE SPARK PLUG. 10X PHOTOS REVEALED CRATERING IN THE SPARK PLUG LEAD INSULATION. PHOTOS AVAILABLE. TEARDOWN OF MAG SHOWED NO ANOMALIES, VISUAL/RESISTANCE CHECK/BOMB TESTING OF ALL SPARK PLUGS WAS NOMINAL. ONLY FAULT FOUND WAS WITH THE IGNITION LEAD. OTHER THAN THE OVERHAULER I WAS THE ONLY MECHANIC WHO HAD MANIPULATED THESE SPARK PLUG LEADS. THEY WERE HANDLED WITH KIT GLOVES. I BELIEVE THIS WAS A MANUFACTURING DEFECT IN THE CHAMPION IGNITION HARNESS.