I am sure others have been as frustrated as I have been upon seeing an “E” core around which sits the coil(s), covered in surface rust. Why can’t a layer of paint be applied prior to fitting, in the factory? Sure, time and money, and it’s not an aesthetic area, so why bother, they all say. Who is going to see the iron core, except mower repair guys, right? I suppose that was why they the manufacturers never went to the effort to paint the E core. But if they had, it would have made for a more elegant finish, and reduced the incidence of small rust flakes getting into places where they become destructive. What’s needed is the Rolls Royce version lawnmower. All stainless steel washers, aluminium alloy bases, full crank 2stroke engines, good quality trip release start, G3 carby, stainless steel handlebars, ...........aah bliss.
The answer is fairly complicated, as such is the construction of the coil. from what I have been reading about transformers (a coil is a transformer) The core is not a single chunk of Iron, but many layers of thin steel. these layers are actually insulated from each other to make it more effective and are actually coated when new. but this coating is very thin, and with the humid conditions mower engines endure, rust comes through very quickly.
Contrary to what you would expect rust actually helps with the insulation between the layers. I have coils that are half as thick again with rust and still work just fine. People get all excited and clean the rust off everything, thinking that they are making it better when it actually does not change a thing..
