What was found
IT IS APPARENT THAT MFG MAGNETOS HAVE HAD THE CONTACT BREAKER ASSY REPLACED IAW SB2-06A, DATED 7/1/06 ARE EXPERIENCING RAPID INTERNAL TIMING CHANGES. THE CONDITION NOTED ON NUMEROUS ACFT EQUIPPED WITH 4300 AND 6300 SERIES MAGNETOS IS ALWAYS A TIMING ADVANCE OF 2 TO 4 DEGREES AT INTERVALS OF 100 HRS OR LESS. BESIDES THE ADDED EXPENSE OF RESETTING INTERNAL TIMING AT UNUSUALLY FREQUENT INTERVALS, THERE IS A REAL RISK OF SERIOUS ENGINE DAMAGE OCCURRING FROM ADVANCED TIMING OPERATION. IAW SEVER PHONE CONVERSATIONS , OWNER OF ACFT MAGNETO SERVICE. THERE ARE NUMEROUS OTHER OPERATORS EXPERIENCING THE SAME CONDITION.