Slick Magneto performance is and always has been less than stellar in terms of reliability and starting performance, when I was running a small fleet of aircraft I always had a spare Mag in the shelf.
It was this unreliability that enabled me to stagger the mag changes so two Mags never got changed at the same time.
The poor starting performance was addressed by fitting a Slick Start to the aircraft , this saved a fortune in battery’s and starter motors as the engines always started at the first attempt even in the hands of the most inept student pilot.
Bendix mags are far more reliable so much so that I can’t remember when the last one I owned failed.
Magneto maintenance is little understood as it seems that a 500 hr check as in the case of this thread been presented as an overhaul, the 8130 states the work done was a 500 hr inspection. So in the case of a slick mag this would be done IAW the SB covering the work and NOT a full overhaul to zero time the Mag.
Out of interest what model of magneto was it and what was the nature of the failure? Slick magnetos have been notorious for impulse coupling problems for a while now.
I have received the following photos from the OP. He was unable to post them (some IT reason)
I’d say that one doesn’t look overhauled, maybe not even IRAN, but only INSPECTED. Last time zero’ed reads 35 years ago, so what number of flight hours have been done on this max life time limit incl extension 2,000 flight hours part? Btw, I haven’t had an issue with my Slick in decades, just got two new one – knock on wood.
Blimey 4250’s have been obsolete for well over 10 years, I’d be doing some serious looking at my own maintenance regime if I still had one of those fitted with that timescale between overhauls.
Pics look like a bearing has failed for some reason and roasted the internals, it certainly won’t be repairable.
Donate it to a museum and move on.
