Much as it pains me to say, me old mate Northern Trent is right.
Both Bendix (TCM) and Slick (Champion) have Service Bulletins covering inspection and overhaul periods of their magnetos.
Service Bulletins are not legally mandatory. In the days of LAMP (still hanging on in there) one technically assesses continuing airworthiness data to justify not complying with it.
There is also the issue that if it appears in an aircraft manufacturer’s maintenance programme it is mandatory. 500 hour inspections are certainly called up for Cessna 152s for instance but for many years weren’t a requirement on the Piper PA28-161.
Of course, with SDMP/MIP etc coming in, an owner can choose to do what one wants (though not less than MIP).Slick SB-80CTCM SB643B
Slick: 500 hour inspections and overhaul/replace at engine TBO
Bendix: inspection (not overhaul) at 500 hours; overhaul after 4 years in service (or 5 years since manufacture or overhaul or at engine overhaul.
My personal experience is that magnetos don’t last any longer if 500 hour inspections are carried out. That said, it isn’t a bad idea to have a look inside and make sure all is as it should be.
Impulse couplings do wear and if an engine starts to get truculent to start then have the magneto’s impulse coupling(s) looked at.
In a previous life and before the 500 hour inspection was introduced into the PA28-161 maintenance manual, I had a long discussion with our CAA Surveyor as to whether they should be carried out or not. I could provide evidence of Slick mags lasting longer if you left them alone and asked for the CAA’s statistics to prove the safety case to have the inspections done. He quoted a Mooney that crashed on take off in Jersey after the dual mag failed. I pointed out that the aircraft took off with a reportedly rough running engine – the second flight after a 500 hour inspection which may not have been carried out correctly. Had the mag not had the inspection the pilot probably wouldn’t have died – not a great safety case for 500 hour checks.
Some companies like Nicholson-McLaren Aviation carry out 500 hour magneto inspections for a fixed price. Other magneto inspecting companies are available.