As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT THE LT MAGNETO WAS NOT OPERATING CORRECTLY. IN THE COURSE OF NON ROUTINE MAINTENANCE THE LT MAGNETO WAS FOUND TO HAVE A BROKEN DISTRIBUTOR GEAR. FURTHER MAINT REVEALED THAT THE RT MAG HAD A 200 RPM DROP WHICH IS OUT OF OPS LIMITS. ALTHOROUGH INSPECTION OF THE ENGINE REVEALED THAT NR 4 CYLINDER SHOWED SIGNS OF DETONATION. DUE TO THE DETONATION IN THE CYLINDER, THE ENGINE ASSEMBLY WILL BE REPLACED.