The Manufacturers Data from SB643, and the relevant Overhaul manuals differs considerably.
S-1200 Series Magneto’s Manual X42001-2 (Aug 2011)
Section 2.3 – Recommended Maintenance and Overhaul periods
(D) “In addition, it is recommended that magnetos be overhauled at the expiration of four years, without regard to the accumulated operating hours since new or last overhaul.”
S-20 / S-200 Series Magneto’s Manual X42002-3 (Aug 2011)
Section 2.3 – Maintenance and Overhaul Periods
(Last Paragraph) “In addition, magnetos must be overhauled or replaced five years after the date of manufacture or last overhaul or four years after the date placed in service, which ever occurs first, without regard to accumulated operating hours since new or last overhaul.”
D-2000 / D-3000 Series Magneto’s Manual X42003-3 (Apr 2012)
Section 2.3 – Maintenance and Overhaul Periods
(Last Paragraph) “Inspect magnetos and harnesses for airworthiness at the expiration of four years, without regard to the accumulated operating hours since new or last overhaul.”
SB643B Maintenance Intervals for ALL TCM and Bendix Aircraft Magnetos and related Equipment
Sect. 4 Engine Overhaul or Four Year Interval
(D) “In addition to the requirements listed above, magnetos must be overhauled or replaced at the expiration of five years since the date of original manufacture or last overhaul, or four years since the date the magneto was placed in service, whichever occurs first, without regard to accumulated operating hours. Also at this time all related components, including the High Tension Ignition Harness, Starting Vibrator Assembly and Ignition Switch Assembly, must be inspected for airworthiness in accordance with the procedures contained in the latest
revision of their respective Service Support Manual.”