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ew1usnr

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Discussion starter · #1 ·
Distributor caps have a center button made of carbon that the rotor contact spins on:



Why is that contact made of carbon and not copper?

It seems like a copper rivet would be more durable.

Thanks, Dennis.
 
Carbon is also self lubricating, and already burned (oxidized) beyond any further oxidation.
 
Discussion starter · #5 · (Edited)
Distributor Caps

I would agree with Dana; its not metal but the carbon probably lasts longer. |
I found a textbook reference that carbon is harder than steel. So ... maybe the answer is that the engineers chose carbon to make the button because it has a round bearing surface and they wanted a conducting material that would not wear away and would not corrode. That sounds plausible.



While on the topic of distributor caps, I had always thought that distributor caps with brass terminals were better and that only cheap distributor caps used aluminum terminals. Aluminum is supposed to burn and pit quicker that brass. And then I was surprised to find that Motorcraft distributor caps use aluminum terminals. Motorcraft is generally supposed to be better quality than most cheap aftermarket stuff. They are a lot more expensive than reproduction caps that use brass terminals.



Motorcraft Distributor Caps B7A-12106-A. $17.97 at Summit Racing. Thermoplastic, Gray, Aluminum Contact Terminals, Ford, V8.
Scott Drake Distributor Caps B7A-12106-A. $9.86 at Summit Racing. Black. Ford V8. Contact terminal material: Brass.

That made me wonder about the aluminum contacts in the distributor cap that is on my car. It is a transparent cap that I had bought off e-bay a couple of years ago for its novelty value rather than for pure function. It lets me see the rotor whirl around in daylight and lets me see a ring of sparks at night. Way cool.





I have a PerTronix Ignitor points replacement and use a 40,000 volt coil and wondered if the higher voltage might be burning up the aluminum contacts. I had driven the car 8,000 miles since installing the novelty distributor cap and I removed it yesterday for inspection. I was pleased to find that the inside of the cap looked perfect. The aluminum contacts were clean and not burnt or worn and the carbon contact button showed no wear. Perfect. There was a little bit of aluminum dust on the face of the distributor that I wiped away with a paper towel.

Distributor caps are supposed to be changed every 25,000 miles when doing tune-ups, but maybe this cap will last longer than that.
 
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I found a textbook reference that carbon is harder than steel. So ... maybe the answer is that the engineers chose carbon to make the button because it has a round bearing surface and they wanted a conducting material that would not wear away and would not corrode. That sounds plausible.

View attachment 535849

While on the topic of distributor caps, I had always thought that distributor caps with brass terminals were better and that only cheap distributor caps used aluminum terminals. Aluminum is supposed to burn and pit quicker that brass. And then I was surprised to find that Motorcraft distributor caps use aluminum terminals. Motorcraft is generally supposed to be better quality than most cheap aftermarket stuff. They are a lot more expensive than reproduction caps that use brass terminals.

View attachment 535873

Motorcraft Distributor Caps B7A-12106-A. $17.97 at Summit Racing. Thermoplastic, Gray, Aluminum Contact Terminals, Ford, V8.
Scott Drake Distributor Caps B7A-12106-A. $9.86 at Summit Racing. Black. Ford V8. Contact terminal material: Brass.

That made me wonder about the aluminum contacts in the distributor cap that is on my car. It is a transparent cap that I had bough off e-bay a couple of years ago for its novelty value rather than for pure function. It lets me see the rotor whirl around in daylight and lets me see a ring of sparks at night. Way cool.

View attachment 535857

View attachment 535865

I have a PerTronix Ignitor points replacement and use a 40,000 volt coil and wondered if the higher voltage might be burning up the aluminum contacts. I had driven the car 8,000 miles since installing the novelty distributor cap and I removed it yesterday for inspection. I was pleased to find that the inside of the cap looked perfect. The aluminum contacts were clean and not burnt or worn and the carbon contact button showed no wear. Perfect. There was a little bit of aluminum dust on the face of the distributor that I wiped away with a paper towel.

Distributor caps are supposed to be changed every 25,000 miles when doing tune-ups, but maybe this cap will last longer than that.

That thing is way cool. How much was that bad boy if you don't mind me asking?


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The only times I had to replace a distributor cap was when they got a carbon track, cracked, or the carbon button gets damaged, almost all caps, just get dirty on the outside and need to be cleaned with some dish detergent and rinsed and wiped dry, or a hair dryer, or some compressed air to dry it out. A pocketknife will clean the aluminum contacts when they get some crude on them. When the cap gets dirty, on humid or rainy days, they can arc across the cap between contacts and cause missfires, or a carbon track across the top, bad spark plug wires (open or high resistance) can cause this also. Here's a little information on the high voltage in a system, in a working system the voltage to fire the plugs, depends, on the compression, the engine load, spark plug gap, the rotor gap to the distributor contacts for each cylinder, plus more. For instance, let's say an engine idling requires 14,000 volts to fire the plugs, and your system can produce a maximum voltage of 30,000 volts, this means your reserve is 16,000 volts when idling, now you accelerate the engine, the voltage to fire the plugs increases to 22,000 volts, now your reserve is 8,000 volts, as long as you have some reserve, the engine will not miss fire for those reasons. Increasing the maximum voltage available to 40,000 volts, by changing components, makes no improvements, as far as the engine is concerned, as you don't have any demands exceeding the 30,000 volts of the stock system. So this means keeping the high voltage components clean, rotor, dist cap, ignition coil top, sparkplug insulators, spark plug wires and dist HV coil wire clean, regardless of what electrical ignition system you use, so you have a reserve voltage under all conditions. My 2 cts. Good Luck.
 
Discussion starter · #8 ·
Distributor Caps

That thing is way cool. How much was that bad boy if you don't mind me asking?
Hello, 90lxwhite. No, I do not mind at all. The cap fits all Ford V8 motors from 1958 to 1976. It cost $14.99 with postage included and came from Midway Industries in Prescott, Arizona. See: midwayindustries on eBay . I bought the cap last year though, and unfortunately it looks like they are now out of the Ford caps. All they have left are Chrysler caps.

Increasing the maximum voltage available to 40,000 volts, by changing components, makes no improvements, as far as the engine is concerned, as you don't have any demands exceeding the 30,000 volts of the stock system. So this means keeping the high voltage components clean, rotor, dist cap, ignition coil top, sparkplug insulators, spark plug wires and dist HV coil wire clean, regardless of what electrical ignition system you use, so you have a reserve voltage under all conditions. My 2 cts. Good Luck.
Hello, REx1965. Understood. You can only pour 8 oz into a cup even if you have a gallon of water. For adventurous souls, however, PerTronix offers an even more impressive 60,000 volt Xtreme coil. Wow!! :smile:

 
Like sex, the promise of more voltage sells coils although what is more important is spark energy. Voltage only starts the spark; its energy that ignites the fuel. We don't really know what that coil will do since it is not in their catalog nor mentioned on their website. You can find several trying to sell coils using the unexplained word Xtreme with a part number for the more standard Pertronix coils.

If your engine misfires for some reason and you have a 60kV spark with sufficient energy it can actually damage your distributor cap when the arc punches a hole through the plastic to find ground. That will leave a carbon track and would be one of the rare times Rex mentioned when you should replace your distributor cap. Otherwise, I have never heard of a mileage spec for replacing a distributor cap. I have cars with 100k+ miles on their caps with no problems.
 
"Clearspark" distributor caps as they were originally called were first sold through the Mickey Thompson catalogs and later in other monthly magazines. The original owner , inventor, sold the company to a friend of mine in 1974 and I ran it for him. Through our racing connections with Stinger Ignitions ( Midway Industries) we sold MANY thousands of caps through them and added red and blue transparent and solid yellow caps. They are made from injection moulded high grade polycarbonate plastic to handle the heat and be non conductive. They were all made and machined in the USA. We did try the brass inserts . They were more expensive and harder on the cutters used to machine them. The carbon "button" was a good conductor and didn't wear like a metal to metal contact would. I left the company in '76 for greener pastures. The caps do yellow up in time. They were more of a fad thing but are still sold today by other vendors.
Randy
 
Discussion starter · #11 ·
Clearspark distributor caps

"Clearspark" distributor caps as they were originally called were first sold through the Mickey Thompson catalogs and later in other monthly magazines. The original owner , inventor, sold the company to a friend of mine in 1974 and I ran it for him. Through our racing connections with Stinger Ignitions ( Midway Industries) we sold MANY thousands of caps through them and added red and blue transparent and solid yellow caps. They are made from injection moulded high grade polycarbonate plastic to handle the heat and be non conductive. They were all made and machined in the USA. Randy
Hello, Randy.

Thanks for providing the background on this distributor cap. It is nice to know that it is a Made in USA quality product. I will now regard it with even greater appreciation.

Dennis.

 
"Clearspark" distributor caps as they were originally called were first sold through the Mickey Thompson catalogs and later in other monthly magazines. The original owner , inventor, sold the company to a friend of mine in 1974 and I ran it for him. Through our racing connections with Stinger Ignitions ( Midway Industries) we sold MANY thousands of caps through them and added red and blue transparent and solid yellow caps. They are made from injection moulded high grade polycarbonate plastic to handle the heat and be non conductive. They were all made and machined in the USA. We did try the brass inserts . They were more expensive and harder on the cutters used to machine them. The carbon "button" was a good conductor and didn't wear like a metal to metal contact would. I left the company in '76 for greener pastures. The caps do yellow up in time. They were more of a fad thing but are still sold today by other vendors.
Randy


I wish they made one for my model.


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