What was found
DURING FLIGHT, THE ENGINE EXPERIENCED A SMOOTH PARTIAL LOSS OF POWER WITH AN RPM DECREASE OF APPROX 200–400 RPM. DISCONTINUED THE FLIGHT & MADE AN EMERGENCY LANDING AT AN AIRPORT OTHER THAN THE ACFT’S HOME AIRPORT. THE MAGNETO HAD APPROX 115 HRS OF SERVICE & WAS CONFIGURED FOR 25° FIXED TIMING VIA THE DIP SWITCHES. DURING TROUBLESHOOTING, THE MAGNETO LED INDICATED 25° VARIABLE RATHER THAN 25° FIXED. THIS CAUSED A DETONATION EVENT IN THE ENGINE. CONTACTED MANUFACTURER & INSTRUCTED TO RESET THE UNIT. AFTER 3 SEPARATE RESETS, THE LED CONTINUED TO INDICATE 25° VARIABLE. DURING THE EVENT, NR 4 CHT INCREASED SIGNIFICANTLY. INSPECTION & BORESCOPE EXAM, SHOWED EVIDENCE CONSISTENT WITH ABNORMAL COMBUSTION/DETONATION. NR 4 LEAKDOWN WAS APPROX 58/80. THE CAUSE OF THE TIMING ANOMALY AND ITS RELATIONSHIP TO THE ENGINE CONDITION HAS NOT YET BEEN CONCLUSIVELY DETERMINED. I AM AN A&P/IA AND PERFORMED THE TROUBLESHOOTING AND INSPECTION.