Some slight tweaks to yours, progressive, so that you’re giving the whole picture.
The requirement for the oil change/filter inspection is clearly set out in AD/ENG/4 requirement A3 for private ops - within the manufacturers recommended period + or - 10%.
But ….
AD/ENG/4 only applies to piston engines fitted to aircraft maintained to Schedule 5.
Further …
AD/ENG/4 ‘points’ to the engine manufacturer’s data.
So…
What you meant to say was:
(1) if a piston engine is fitted to an aircraft maintained to Schedule 5; and
(2) the engine manufacturer’s data specifies oil/filter changes more frequently than e.g. Annually/100 hourly,
the outcome is that AD/ENG/4 mandates the more frequent changes, subject to the margin specified in the AD.
What those periodicities happen to be change from engine-to-engine type/part number to engine type/part number.
Also…
It’s possible for the aircraft to be maintained in accordance with a system of maintenance (i.e. neither Schedule 5 nor the manufacturer’s maintenance schedule, although I concede that a system of maintenance would normally reflect the engine manufacturer’s oil/filter change recommendations).
Re ignition systems: You obviously think you know lots about ignition systems, but have learnt very little. Do a search on the Champion massive electrode internal resistor problem.
You 'gap' fine wire plugs? You’re not going anywhere near my engine.