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Solid wire or carbon core spark plug wires (long)

U

used red MN

Well-known Member
Location
Coon Rapids, MN
I see in a recent post on one of the brand specific forums as well as several instances on other boards a post has been made about problems with a misfire. The tractor in question has the normal point and coil ignition as most tractors in the era that are discussed here have. Quite often one of the replies question if the tractor has solid wire core spark plug wires. Then the poster giving the help rants on for a sentence or two how the tractor just won't be able to run with a carbon center suppression type spark plug wire. The Farmall M I have has a mix of both due to through the years when a misfire problem would develop what ever was stored on the shelf of the farm shop is what was thrown at it until the problem was corrected and then back to doing the job it went. Obviously that is a "shoddy mechanical repair approach" but it runs fine purring along on all cylinders. So let's say from the late 50s through the mid 70s hundreds of thousands of cars were produced and sold with carbon core suppression wires and went probably millions of miles fairly reliably. Many of these vehicles use the same brand of ignition systems as our trusty tractors as an example Delco or Motorcraft. So with that why are carbon core suppression spark plug wires such a "bane" for tractors? I know one of the reasons will be the tractor was not originally equipped or designed to use them, but let's get some good reasons beyond that. TIA Rick
 

Unless your machine has an AM broadcast radio receiver, you are a Ham working the 10M band from your tractor or you need an aviation radio on your tractor. Use solid core wires and non resistor plugs.
There are spiral wound wires that give the best of both solid wire and radio suppression.
 
I've never understood the concern. I have several tractors with solid copper and several with carbon filament. I can't tell the difference. And, carbon filament wires came out long before cars went to electronic ignition. Not much difference between the coils, condensers, and points.

Does anybody have a real reason to not use carbon filament wires? They work for me, and I work my tractors.
 
Magneto vs distributor....Carbon core wires don't work well with magnetos. Why? I don't know, but they don't. I too have a set of carbon core wires on one of my Ms. Been on there since the 90s and it runs fine.
 
Yep, and as Buick posted don't forget about the wire spiral-wound "magnetic suppression" wires!

If a "Kettering" ignition system is in good condition, as well as the charging system, carbon core wires will function just fine, even on a 6 Volt tractor.

On the other hand, though, if the tractor is run out in the country, away from houses/occupied buildings, etc. with people who will be irritated by the EMI, the "solid core" wires are just fine.

Typically, suppression wires are suggested/required on engines with EI, or EFI.

On the other hand, it is typically suggested NOT to use carbon suppression wires on engines with magnetos because the extra voltage needed from the coil to fire the plugs puts extra stress on the insulation (not to mention a mag likely has an older coil with poorer insulation to start with than modern coils, and has been put through years of use, heat/cool cycles, etc.).

Just MHO!
 
I vote for a conductor that keeps the electrons in and flowing. The total resistance of the spark gap at the plug and within a spark gap plug, within the cap from rotor to posts, and the wire, determine the total voltage needed to spark. The carbon wires and spiral wound magnetic suppression wires and solid conductor wires all work to do this.

Carbon wires breakdown internally most often, but suppress radio noise

Plain wires are reliable but radiate electromagnetic radio frequency noise

Wound wire type suppression wires are robust in reliability, have little resistance, and suppress RFI

There is no difference between applying them to an ignition system of any type. The carbon wires can increase the spark voltage in that they can have 8 to 10 thousand ohms per foot of run.

I say make the connection and run it. Jim
 
Carbon wires and resistor plugs were introduced as measures to supress ignition noise particularly on auto radio receivers for AM radio band. Since this brings restance into the system and thus changes characteristics of the ignition system. You would probably be best served to use similar wires to those your tractor came with. To replace copper with carbon may compromise your ignition performance.
 
Thanks for all the replies and sharing of knowledge. I can now apply this intellect and common sense when deciphering these ignition related post in the future. They will also help me veer from my original hunch which leaned toward the direction of Bob Bancroft's stance. Thanks again and great discussion! Rick
 
I have been outnumbered again! I did use the word "nearly". I suppose because few things are absolute. Certainly there are situations where the conductor makes a difference. But on your tractor, it's apparently totally irrelevant.

Are you going to ask about oil next?
 
Well while waiting for John T to get on and answer, I will make a feeble attempt. On a coil/bat ignition system,I don't think it makes a diff as long as they are in good condition,in other words compare new to new. Now on a magneto ignition , which is probably what the posts you are referring to are talking about , there is no external power source feeding the coil and magnets have a finite amount of power that cannot ramp up just because a resistance is sensed as the other can. Therefore , any resistance between the mag and plug (including the plug itself) will affect the power to make spark. A coil/bat system has plenty of reserve and way more power than it needs to overcome resistance and actually make a hotter spark because of it. Not so with a magneto on the old tractors. A magneto on a nitro burning dragster was designed to fire a mixture of "syrup" and alcahol under extreme pressure conditions but these old tractor mags don't need and don't like resistance. I'm sure John "T" will chime in with the real answer.
 
A mag is operationally similar to the Kettering system. It produces voltage in the primary by spinning a magnet in proximity. This current is at producing the same amps as found in a conventional coil. The points break and voltage rises till it sparks. Most mags can produce 20,000 volts. Unless weak magnets, or a conductor path to ground, it performs the same way, Dwell saturates a Kettering coil, magnetism of the rotor saturates the mag coil. I say no difference. Not intended as a flame. Just what I maintain is reasonable. Jim
 
No "flame" taken here, just reasonable discussion. I have another question tho. Since a coil doesn't "know" what load lies in it's path, I would think all it "knows" is how much energy is entering it and for how long. If that's true then it will work at it's max every time points are closed. Now it may not take it all to fire the plug but it still made it all. If that is true then the only thing that would "overheat" a coil would be the number of times in a minute that it was called on to do it. If that is true then would that explain why a coil for an 8 cylinder engine that might turn 5000 rpm would have to be larger and oil encased, whereas a coil in a JD 2cyl tractor that only has 2 cylinders and 1100 rpm might be 1/4 the size and no oil? What say you?
 
A magneto does not make strong spark at low RPM so solid wires are used due to less resistance. A bat/ Coil it does not matter. A magneto is an AC device. Not so important on a tractor as a kick start motorcycle with a mag.
 
I don't have any articles (on hand that I have saved) but based soley on my experience and literature Ive ran across over the years, I believe its less critical on a battery powered coil ignition (as to the use of wire core versus higher resistance carbon core wires) then it is on a generally lower energy magneto ignition. I read somewhere that in general, based on RPM and magnetic field strength of the rotor, and based on the impedance of the load into which the mags output is connected, ITS BEST IF THE LOAD (part of which is the plug wires) IS LOWER IMPEDANCE and wire is less impedance then carbon.

Subject to RPM and magnetic field strength (on a mag) its my understanding in general a typical old tractor mag produces less energy then a battery powered old tractor ignition and since plug wire current yields I Squared R heat energy losses its NOT good to waste any limited precious spark energy in the wires but best to discharge it all across the plug gap.

If the energy is limited to begin with, and the mag is less energy then a battery ignition, why waste any in the form of I Squared R heat loss in higher resistance plug wires??????????

NOTE I know Ive read this before and didn't dream it lol but its my belief wire core wire is best to use on a Magneto (because energy is limited so why waste any in the wires), although sure, either will still work well duhhhhhhh but I just dont have any hard core research or articles Ive saved to cite to back that up

That's my story n Ima stickin to it for now at least lol but Ive been wrong before you know

John T
 
This is a sacred cow, and you're not allow to slay sacred cows on this forum!

It's a simple fact that carbon core spark plug wires are less reliable than copper wires. That said, there's no reason quality carbon wires shouldn't work just fine on your tractor.
 
When I get done servicing a mag I install in the vice then using drill motor I can turn it over with wires and plugs connected I can observe fire at all rpms I don't notice any difference in spark.
 
I found it's not so much the wires but the gas that causes the miss. Check the octane in the gas you have in your tractor and see if it's the same you buy at the gas station. I do know that you can't use carbon core plug wire on a magneto.
 
If you switch from point ignition to electronic ignition you need to switch to carbon spark plug wires.
 
Jim: Looks like the magnetic field comes from the atoms of the material. Thus the solid wire makes a field where the carbon does not. Also it is excited by the voltage not the current as there is little current in these wires.
 
Path of least resistance.

Ever notice a slightly degraded carbon core wire will cause an intermittent or total misfire, worse when raining and wet.

With the higher resistance in the carbon core wire the occurrence of the spark jumping out of the insulation to a valve cover through the side of a wire or right out of the boot to the head before it reaches the plug is greatly increased.

An old solid core wire with nasty insulation cracked to the point that you can sometimes see the exposed wire can continue to deliver the juice to the plug and keep the engine running right.

Comparable to how a garden hose with 10 pin holes does not leak until you put your thumb on the end of it, at which time much like electricity the water will exit the hose wherever the least resistance is found.
 
As I was told by an older MM dealer on my M670 Super that it will run fine with the suppressor style wires but wont have enough "poop" to push the spark through under load. Im guessing you might lose a little power that way.
 
Dwell is the amout of degrees of distributor rotation that the points are closed. Dwell is usually close to 50% of the allotted time for each cylinder. The larger the dwell (kettering) the longer the coil is turned on and the greater the saturation of the buildup of magnetism in the coil body. As RPM increases, the time allotted, in milliseconds, decreases. If 8 cylinders in a car turning 4500 rpm are discussed we can see that the saturation time per spark goes way down. But !!! the % of on time remains the same at about 50%. Thus the coil heat buildup is the same at all speeds except stopped. When stopped, the coil is almost always on if the key is on. Thus burning up the coil because its duty cycle is 50%, not 100%.
Mags need rotor speed to make sufficient voltage when hand cranked (essentially no rpm) and thus must have an impulse coupling to hold back, then release the rotor so it spins as fast as the tractor Idle speed or more. at that RPM the energy is saturating the primary windings and coil very well. Thus the magnetism is sufficient to build magnetism in the coil laminations and throughout the secondary windings such that when the points break, the collapse is sufficient to build voltage till the resistance of the gaps is overcome. Remember that at higher RPm the time for saturation buildup is reduced for both Kettering and mag systems. I hope this helps. Jim
 
(quoted from post at 08:40:19 02/01/16) I found it's not so much the wires but the gas that causes the miss. Check the octane in the gas you have in your tractor and see if it's the same you buy at the gas station. I do know that you can't use carbon core plug wire on a magneto.
Click to expand...

Explain that
 
both my Ford Ns had carbon core but I've switched them both over to copper core. Eliminates one source of possible problem. Do a resistance check on the carbon core ones and you'll see what could be an issue. Just my opinion, use what works for you.
 

In my experience 'solid' wires will outlast the carbon-core 'suppression' type as the internal resistance will increase as they age.
 
Taking in account all the responses on here , I would boil it down to this then. If everything is "new" and assuming it was made correctly and adjusted correctly, probably no advantage either way as far as wires design. Since we all know that isn't "real world" and we all know they are not made equal quality and all start deteriorating the day after they are born (plugs and wires both) , and once is probably all a hobby/collector tractor will ever get, then I would summise that a solid copper core wire and plug combination would be the best value and sustained carefree performance and that an aged /weathered set would probably show a performance/ reliability advantage between the two types. Now I'm not sure this difference would show up any more on a mag as apposed to bat/coil ignition. All indications say it would be equal. That leads me to believe that the mag/solid wire concensus may come from the fact that mag tractors are older , used less , neglected more so any of them that were ever fitted with "new" carbon wires/resister plugs for whatever reason probably have a marginal path to the electrode by now even tho they may look new yet. Like one poster said, and I believe it , a solid copper core all the way to electrode would work fine even with no coating and in the rain as long as kept away from metal whereas a broken down carbon core will resist so much the current will leach out and find a new easier path. Guess that's all folks.
 
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