# 80% platinum/20% iridium Old Magnetos



## Anonymous (Feb 12, 2008)

Old magnetos could have platinum contacts inside, a good read I came across over the net.



*Platinum vs. Tungsten points*

Over the many years a magneto has been on the road, it is likely that some service has been performed on it. The most likely being replacement of the points and oiling the bearings. 

Most magneto manufactures specified the use of platinum points as opposed to tungsten points commonly used in battery and coil ignition systems. If tungsten points have been installed in your magneto, it may work fine for a while but it will soon lose its ability to provide a hot spark under low RPM.

Platinum is usually alloyed with iridium (80% platinum/20% iridium) to attain toughness and hardness of the contact point, which gradually enhances its electric value. Pure platinum would hammer under the action of the contact breaker. 

Platinum has the property of a very high fusing point and does not oxidize under ordinary conditions. It has a very low surface resistance, which remains throughout the life of the point. While it is subject to a certain building up and pitting process, this process extends over the entire surface of the point, with the result that the contact area is not impaired. It has long life and can be used down to the last few thousandths of an inch.

Tungsten points are primarily used with battery and coil ignition. Tungsten is extremely hard. It withstands the hammer type blows caused by the high spring tension, which is necessary in high speed interrupters and to maintain good contact at the point surfaces. 

It is not rapidly consumed by electrolysis, but it is subject to oxidation, and inherently has a high resistance. This oxidation results in a high resistance oxide film coating on the points, reducing the flow of current. Thus a high voltage across the points is necessary (usually 6 volts from the battery).

The disadvantage of tungsten points in magnetos is the oxidation of the points and the high surface resistance. Both of these factors prevent the magneto primary current building up to its maximum value, resulting in weak current and hard starting. 

Arcing across the points is more common with tungsten than with platinum, and it is more difficult to determine when a condenser is defective. When platinum points are used, extreme arcing is always an indication of a defective condenser. Tungsten points require a greater condenser capacity to overcome arcing than do platinum points.

So how do you tell if your points are platinum or tungsten? First off platinum is a much softer than tungsten. A fine tooth jeweler’s file will cut them very easily. Tungsten contacts are much harder. Try your file on an old set of tungsten points from Aunt Betsy’s 69 Buick. Then carefully dress your magneto’s points. If they are platinum, you’ll be able to tell a big difference. 

Another way the old timers used to tell the difference is to put a few drops of nitric acid on the contact. If the acid eats into then points they’re not platinum.


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## Lou (Feb 12, 2008)

Um not if they're platinum-iridium alloy. Iridium is very hard, and makes platinum very hard. I think a file might have trouble cutting it.


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## AuMINIMayhem (Aug 21, 2008)

don't forget.. tungsten has some value as well.. don't cut your nose off to spite your face..


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## Richard36 (Mar 22, 2009)

Wait a minute, contact points on small motors contain PGM's? If that is so, then I have allot of contact points around here just laying around as steel scrap. If I am understanding you correctly, I will be salvaging some contact points. :shock: :!:


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## Palladium (Mar 22, 2009)

I have a friend who is an electrican and about a year ago he brought me a box full of old GFI wall outlets ( about 200 ) he removed from a job he was working on. The contacts were silver. 8)


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## AuMINIMayhem (Mar 24, 2009)

Palladium said:


> I have a friend who is an electrican and about a year ago he brought me a box full of old GFI wall outlets ( about 200 ) he removed from a job he was working on. The contacts were silver. 8)



Nice! 

any yield data?... my uncle is an electrician and is always throwing stuff out.. I got him bit by the "copper bug", so now he keeps all the copper and brings that up to the recycling center every month or so.. he's made quite a bit on that alone.. was there enough silver in those old outlets for me to tell him to set them aside? how hard was it to crack open the outlets to get to the contacts?..

actually, do you have any pictures I could show him as a refence? (or a part number)

Cheers!
Derek


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## Richard36 (Mar 24, 2009)

Some where on this forum I read that spark plug electrodes contained silver and PGM's. Is that so with all spark plugs? A response would be greatly appreciated. Thanks. Rick.


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## Lou (Mar 25, 2009)

Spark plugs are usually platinum, iridium, and alloy thereof, or for cheaper ones, copper. I think silver is also used.


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## Richard36 (Mar 26, 2009)

Well if that is the case, then spark plugs are a definite get. I do some automotive work on the side, and know plenty of other people that do as well, Let alone all the service centers around here. Spark plugs, huh? I will be looking into this. Thanks. Rick.


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## AuMINIMayhem (Mar 26, 2009)

I have a tendency to suspect that spark plugs would be a bit labor intensive versus the yields... I may very well be wrong though.. :wink:


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## Richard36 (Mar 26, 2009)

I have a rock crusher. It would be easy for me to pour them through it to crush them, then sort out the electrodes from the ceramic and steel bases. The electrodes could then be processed chemically. That would be my plan anyway. Thanks for the info. Sincerely; Rick.


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## Sodbuster (Mar 26, 2009)

Richard36:
I cracked open an old Bosch Platinum plug once to see just how much platinum i could find. I found a little hair sized piece about a quarter inch long, the tip that you see at the buisnes end of the plug. Point it straight up in a vise and wedge something in beside the center electrode and you'll have the portion containing the the good part. The rest of the center electrode looked like some kind of graphite ceramic, prolly for radio supression. I didn't think the ground electrode was anything precious. I know plugs vary, but it's prolly just the very tip of the + electrode that your after. Crack the centers out and through them in your rock grinder. 
Just a thought --- Ray


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## qst42know (Mar 26, 2009)

AuMINIMayhem said:


> I have a tendency to suspect that spark plugs would be a bit labor intensive versus the yields... I may very well be wrong though.. :wink:



If an automotive "platinum" spark plug sells for around $5 how much platinum would any sensible person suspect they contain? It is a tiny little tip only on the end of the center electrode. 

If you had a drum full maybe.


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## Sodbuster (Mar 26, 2009)

I agree very small, I don't even think a drum full would yeld enough to cover the bottom of a 500 ml beaker. From what I've seen 
Ray


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## Richard36 (Mar 27, 2009)

You both may well be right. It seemed like an intriguing idea though. I am new to scrap, so any help, and ideas are appreciated. Sincerely; Rick.


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## qst42know (Mar 27, 2009)

I didn't intend to discourage you. If I had a source of plugs I would probably save them as well. Kinda like having a change jar if you do it long enough you will end up with something. :wink:


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## Richard36 (Mar 27, 2009)

No offense taken. The thought was rather intriguing though. As I have said, I am new to e-scrap. My specialty is Ores and Minerals.


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## rusty (May 9, 2011)

gustavus said:


> Old magnetos could have platinum contacts inside, a good read I came across over the net.
> 
> 
> 
> ...




For those of you that want to learn how to grade your scrap, once you learn the ropes you can talk turkey with your local scrap buyer or tell him to go pound salt, because now you can prove that he is trying to screw you out of your hard earned cash.

Anyhow the PDF file is a good read, you may actually find some new things to keep an eye open for from reading this file. It covers everything right down to precious metals.

Also confirms what I said earlier in this thread dated February 12th, 2008, 4:10 pm that old magnetos have platinum contacts.

Regards
Rusty


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## Dan Dement (Jul 4, 2012)

Gustavus,

I have recycled quite a large lot of older Aircraft Platinium magneto points for a customer of mine. I did not keep a picture but the Platinum was only a dot on both sides of the breaker points. Most of these were 40's thru 50's era Government surplus military points. Seems like it was in the $60,000 area a couple of years ago. Understand that this is an unusual find of new points from new magnetos from 6 decades ago. Not your usual junkyard find!

Dan


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## rusty (Jul 7, 2012)

Dan Dement said:


> Gustavus,
> 
> I have recycled quite a large lot of older Aircraft Platinium magneto points for a customer of mine. I did not keep a picture but the Platinum was only a dot on both sides of the breaker points. Most of these were 40's thru 50's era Government surplus military points. Seems like it was in the $60,000 area a couple of years ago. Understand that this is an unusual find of new points from new magnetos from 6 decades ago. Not your usual junkyard find!
> 
> Dan



Right you are Dan, contacts from early 1900's mags upwards into he late 1930's with possibly some still showing up as late as the 50's. Not your everyday junkyard find.

I can see them still using platinum on aircraft mags even today, but as you say with very small PGM button used for the contacts.


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