[AT] Points

[Stephen Offiler]

Hi Ron:

I should have stated that I was conjecturing about the cadmium
construction.  Back about 20 years ago I was employed by a manufacturer of
circuit breakers and the contact material of choice, by a wide margin, was
the silver-cadmium I described.  I had stuck in my memory that this was
also used on breaker points.  Not necessarily accurate!!

I just took a real quick look and it seems platinum was actually alloyed
with iridium to make it harder, and that was used in magneto points.
However, battery and coil ignitions, according to the big wide Internet,
used tungsten to better withstand the hammering they go thru.

SO



On Thu, Mar 9, 2017 at 9:58 AM, Ron Cook <ron at lakeport-1.com> wrote:

> The old points and aircraft magneto points are platinum.  If not burnt
> and thereby pitted, will give no problems.  My opinion, of course.  They
> are very hard and require the points(used to be called platinum)file to
> resurface.  My aircraft stored in the exact same place as the tractors
> and some old engines that never have a problem is my experience.  I also
> have never heard of Ivan's very interesting emergency system.  I will
> also state that I have the points corrosion problem regardless of 6 or
> 12 volt.
>
> Ron Cook,
>
> Salix, IA
>
>
> On 3/9/2017 6:34 AM, Stephen Offiler wrote:
> > Ivan's "emergency" ignition system is pretty interesting; never heard of
> > that before.
> >
> > John, I do own a points file but I'd have to go digging to find it.  I
> use
> > a piece of "wet-or-dry" sandpaper (dry of course) with a grit somewhere
> > either 400 or 600.  I'm reluctant to take off too much material.  Points
> > contacts used to be made of a multi-layer material with copper core (heat
> > transfer) then some silver-cadmium alloy in a measureable thickness, not
> > just a plating.  That stuff has some magic metallurgical property that
> > resists corrosion, resists micro-welding if there's any arcing, and
> resists
> > or prolongs that inevitable material transfer (those hills and valleys,
> the
> > reason you eventually need to file them)
> >
> > Now I just said "used to be made of" because I strongly suspect the
> cadmium
> > has been removed and along with it goes some or all of the magical
> > properties.  So they're more prone to all the bad stuff mentioned
> above.  I
> > think my points must be new enough to be made of the inferior materials.
> > But they have very low hours and show no signs of wear and pitting.
> >
> > I was curious to see if others have similar trouble, and if there are
> > clever solutions.  I realize I really should lean towards that Pertronix
> > electronic ignition retrofit.
> >
> > SO
> >
> >
> >
>
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