[AT] Coating for small engine mag

[Ken Knierim]

Larry,
     With all due respect, maybe I misunderstand your statement but
electric materials are, by definition, insulators. Please see
https://en.wikipedia.org/wiki/Dielectric

Magnetic fields and electric fields are certainly different. There are no
magnetic insulators, but there are lossy materials. Red rust is generally
an iron oxide and it's not the same as the silicon steel generally used in
transformer laminations in a few key respects. It has hysteresis that
translates to magnetic losses in a varying magnetic field (the same field
that induces electricity in the winding that creates the spark). It also
can affect the fringing fields which define how far the fields extend.

Straight iron (such as rust from the steel laminations) can be charged with
magnetism. Hit a nail (or a magneto magnet) with a magnetic field and it
will retain a certain amount of the magnetism. The silicon steel in the
laminations is designed to resist this or it would charge up and resist the
change of the magnetic field on the next rotation. So there is loss and it
dissipates energy lost charging and discharging the iron into a magnet as
heat.

If rust sticks to a magnet, it is interacting with a magnetic field. It
will also channel the field as you note, and if it's not channeling the
correct direction you'll also get degradation of the field. This isn't
usually significant when running but during startup it's most needed and
most detrimental.

Cleaning off the rust and putting a light coating of a rust-preventing,
dielectric coating (many great suggestions have been presented, glyptal
used to be real common for this) is prudent in my opinion. It's not my
stuff though.

Ken in AZ




On Fri, Dec 8, 2017 at 10:25 AM, Rena Glover Goss <rlgoss at twc.com> wrote:

> Umm.  Hey guys!  This has been an interesting thread, but I think there
> are a lot of "old wives tales" floating around on it.  Please learn the
> difference between a dielectric and an insulator, and that magnetism works
> differently than electricity.  You can channel the shape of a magnetic
> field, but there is no such thing as a magnetic insulator.  Just because
> red rust is non-magnetic does not keep a magneto from working, and
> polishing or painting the laminations of an electro-magnet will have no
> effect on its operation.
>
>
> Larry
> ---- Ken Knierim <ken.knierim at gmail.com> wrote:
> > 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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