[AT] Coating for small engine mag

[Ken Knierim]

A lot of modern electronics are potted with a very thin layer of plasma
deposited PDMS. I would guess that in the case of the small engine ignition
parts they aren't coated as that material is a bear to make electrical
contact through once it's been applied. It's tough to see too; it's very
thin. It's largely replaced lacquer because of the environmental and
handling issues except in potting of magnetics (they're still lacquer
dipped in many cases).

For me, I'd consider using some sort of lacquer, either dipped or sprayed
on heavily to prevent moisture from getting into the coil. If it has a
magnetic pickup side (next to a flywheel with a magnet for instance),
you'll want a light coating of something non-conductive to keep the rust
off the cores as rust degrades the magnetic operation. You also want to
keep this layer thin as you need to have a rather specific gap between the
magnet and the core laminations. The magnetic field drops off at the square
of the distance and a large gap can make it a bear to start.

As far as the points are concerned, the newer (cheaper, "environmentally
friendly") metals don't hold up well to corrosion and arcing. Arcing can be
mitigated by using the proper condenser (or an electronic ignition) as I
remember this being a subject of my old 4-H Petroleum Power manuals (how
the arc erodes the points could tell you if the condenser size was wrong
and how to adjust for this).
Since chromium and other materials formerly used in points manufacture that
resisted corrosion can be expensive and have toxic application phases (like
hexavalent chrome), manufacturers in this country can't use them. Silver is
good but very soft (and not cheap) and silver is one of the few metals
that's also conductive in oxide form. (the other I can think of is ITO,
indium tin oxide, which is also transparent and you're probably actually
looking through it right now in your LCD computer screen.) Lots of contacts
(heavy AC contactors for example) use silver and other metals to provide
good contact when exposed to air... these are usually costly and most
ignition points are considered wear items (meaning "keep 'em cheap") so
quality isn't what it used to be. So keeping them clean requires regular
maintenance or a dry environment because anything that drives the water o

Sorry for all the off-topic stuff this morning. Mind is wandering from lack
of coffee.. Hope some of this helps someone.

Ken in AZ


On Fri, Dec 8, 2017 at 4:41 AM, Henry Miller <hank at millerfarm.com> wrote:

> I'm sure there is a reason, but I would guess cheap. These engines are
> designed for machines that are expected to be replaced every 7 years or
> so. If it runs that long they have their money and the customer thinks
> it was reliable since it lasted that long. That it could last much
> longer with just a little more cost is a bad thing.
>
> --
>   Henry Miller
>   hank at millerfarm.com
>
> On Thu, Dec 7, 2017, at 08:24 PM, John Hall wrote:
> > I've can't ever recall encountering a flywheel magnet or a magnet inside
> > a magneto that was coated---must be a reason.
> >
> > John Hall
> >
> >
> > On 12/7/2017 1:25 PM, Mike M wrote:
> > > My wood splitter wouldn't start the other day, had plenty of gas, wet
> > > plug, but weak spark. I suspected rust on the flywheel, so I tore it
> > > apart and I was right. Cleaned it up, and now have a nice strong spark.
> > > Question is, can I coat the mag and coil pickups with anything to
> > > prevent the rust from re-occurring?
> > >
> > > Thanks,
> > > Mike M
> > >
> > >
> > > -
> >
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