Spark Plug Lead Rebuild Plug End

[proppastie]

I have a bad plug end on a lead....and it causes radio noise which goes away when doing a mag check......the bad lead corresponds to the proper mag when I do the check. I twisted the nut once without holding the ferrule and destroyed the shielding at the ferrule. I think the easiest fix is to cut off and the plug end and slide the assembly up and properly assemble the lead with the shield intact......I am pretty sure I have enough lead to allow for that.........I find I can not buy the parts to just do that part of the job .... purchase of a single lead will require removal of the back of the mag (and whole harness) or I can replace the whole harness.


Has anyone been able to knock out the "Drive Ferrule", and remove the Screw and Spring and re-use them?

 

[TFF]

If you are careful, you should be able to reuse it. Lots of newer wires have plastic imbedded in the shield mesh, make sure you scrape it off to make a good connection. If it’s a fail, get a replacement wire and change at the cap end; it is easier. You don’t have to remove the whole harness, just get access. You should be able to get all the parts, they are usually just numbers in a catalog. You are not going to get pictures Champion Terminal Kit CH1K002 | Aircraft Spruce

 

[proppastie]

they are usually just numbers in a catalog.

Preferred Airparts had the items.....$ 20 minimum.......I cut off a bad lead from a bad harness a friend had and the pin and spring on that item was crimped.....so at least a new pin and spring is needed I was able to salvage the drive ferrule from this item but with the $ 20 minimum I ended up ordering them.....I will give the extra parts to the friend I bowered the tool from after I am all done.

 

[Pilot-34]

You might as well keep the parts and tools it looks like you’re the one that’s going to do the job not your friend .

 

[TFF]

That’s the way it goes sometimes. At least you got it figured out.

 

[GeeZee]

Timely post. I’m pondering the same thing. I have a harness that has 3/4“ B nuts at the spark plug end and I need them to be 5/8”. I’ve been wondering how necessary that multi hundred dollar tool is (thats listed in the above attachment). It looks like small vice grips with a couple of small dia tubes welded to the jaws.
I’m also considering the g3i mod that lets you use auto plug wires and auto plugs with a mag. Anyone have any experience with g3i?

 

[Dana]

When I redid the ignition on my Fisher I bought NOS Slick leads (M6202-72) on ebay, cut them to length, and assembled them into the distributor cap. As I recall they weren't too difficult to assemble and I didn't use any special tools.

 

[proppastie]

I didn't use any special tools

I’ve been wondering how necessary that multi hundred dollar tool is

Since I got it I will use it.....reading the instructions one needs to press in the drive ferrule .....off the aircraft on the bench I think it would be fairly easy to figure out a way without the tool as Dana said.....however if you have ever worked on a Mooney you would know there is very little access to the mag if you want to repair a lead and install say just one......There is a little more room at the plug ends but trying to tap/drive the drive ferrule into a hanging wire should take at least 3 hands so the tool will come in handy there.

For a homebuilt I would think those automotive plugs make a lot of sense.

 

[GeeZee]

Yea, I’m warming up to going with auto plugs/wires. I haven’t heard of a lot of people going with auto wires/plugs with a mag though. Apparently g3i does successfully.

 

[TFF]

The issue with auto plugs and mags is noise. Modern airplane plugs ground the shielding at the plug and mag. Car wires don’t. Old planes didn’t have closed loop shielding and didn’t have radios. Once people started putting radios in they had to convert to shielded wires and plugs. See an old plane with a couple of blisters at the front top of the cowl, that’s because new style plugs and wires are taller. A friend with his champ didn’t want to have the blisters. He could get all but one shield plug under the cowl so he has one that still gives a little radio noise. I don’t know how they fix that problem with the auto wire sets. Maybe a wire ground at the plug?

 

[Dana]

In cars you have resistor wire, but I'm not sure if a magneto has enough voltage to push through it?

They used to have stamped sheet metal covers for the unshielded spark plugs, they tied into shielded leads. Great Plains sells something similar nowadays, it's a machined cover that goes over the plug and ties into the standard Slick wires. I had them on the half VW on my Fisher and they worked quite well.

 

[TFF]

Normal airplane plugs have a resistor too.

 

[Pops]

In WW-11 some jeeps that was made for amphibious landing was fitted with an intake snorkel and an exhaust snorkel and the un-shielded spark plugs were in a can with a screw top and a shielded harness was attached to the side of the can with the spring contacting the side of end of the spark plug making it water proof.
My 1947 Ercoupe had the factory option of having these cans for the top unshielded spark plugs . The cans were shorter than a shielded spark plug and no blisters was required for the top cowl.

 

[GeeZee]

Hmmm, I think the resistor plugs are the noise suppression. I think people experienced ignition noise when they tried using non resistor 18mm tractor plugs (the intent was to eliminate the screw in plug adapter). Electronic ignition in aircraft is very popular now. Almost all of them use auto plugs and there seem to be very few complaints of ignition noise. There have been lots of discussions about all kinds of ignition combos over on VAF over the years. I can’t find the conversation I’m thinking of but one seemingly knowledgeable person had a concern that it would be possible to overload a mag coil. I can’t really recall what that condition was but it may have been trying to use a large “auto gap” instead of the smaller gap we use in aircraft mags. Maybe a call to g3i or SDS might be in order…

 

[TFF]

The resistor helps noise. There is degrees of noise. It may or may not matter. Mags are dirtier than electronic ignition for noise. One reason car plugs don’t have as many issues with efi. . A friend runs them in his RV. Tempest spark plugs want you to toss plugs with more than 5000 ohms. Champion doesn’t care. I have seen high resistance plugs cause bad spark issues, and if the resistance on plugs are close, it keeps the mag happy, not dealing with some plugs that are hard to fire. that makes the mag run hotter with a catch 22 of diminishing returns over time until it does break. Wires too. It’s always going to depend on exactly what one wants. 20,000 ft IFR has different issues than a Piet with no radio.

 

[proppastie]

I wrapped safety wire to the exposed shield then to the plug while waiting for the parts..... Solved the problem......Friend suggested that radio still had a weak capacitor which is why it had lots of noise and the other one had hardly noticeable noise.

 

[proppastie]

Question came up....do automotive leads have shield. .?... How come no noise?

 

[Dana]

Automotive leads are resistor leads to suppress noise.

 

[Dan Thomas]

Tempest spark plugs want you to toss plugs with more than 5000 ohms. Champion doesn’t care.

Champion might care now that they fixed their resistor problems. When testing plugs after gapping and cleaning, on a calibrated spark tester, I found many, many Champion plugs misfiring long before the bomb pressure reached 135 PSI. Tempest, almost never. And Auburn before them, never. Auburn were the best aviation plugs ever built. If you ever come across any, buy them.

Champion's resistor was a carbon slug inside the plug, held in by a short screw and a spring. Vibration and heat would make that thing wiggle in there and it would dirty up its contacts. Champion built plugs like that for decades, even after they bought up Auburn and shut them down. It took a LOT of complaining from a mess of us before they very quietly adopted the Auburn technology they owned. This was a big deal over on Pilots of America a few years ago.

The old Champion design they foisted on us for so long:



Note the short screw pushing the spring down onto the carbon resistor. You could take one of these apart after testing it OK, take that screw, spring and resistor out, put it back together, and it would fail the spark test.

Their newer plugs:



See what they did there? They molded the resistor into the plug. No relative movement possible. Auburn's technology, as used by EVERY automotive plug for a gazillion years already.

If someone is going to sell you Champion plugs, look down the connector well and see if the contact button has a screw slot in it. If it does, don't buy it. It's an old design plug.

A good article on it here: Champion Aerospace: From Denial to Acceptance |

Now, Busch talks a bit about the resistor's function. There's a bit more detail to it. The resistor has the effect of cutting off the spark as the voltage falls, shortening the spark time. It doesn't reduce the current that much, since the current is tiny and the voltage very high. Do the E = I x R figuring and see that. The spark needs to be hot, but it doesn't have to keep sparking long after the fuel has caught fire. That just erodes the plugs.

 

[Dan Thomas]

The plug leads are little radio antennae. The laws of electrical physics tell us that when electrons flow through a conductor, a magnetic field is generated. The opposite is also true, but that's a discussion for another time, although that law is used by the shielding to turn the magnetic field back into electron flow in the shield, and taken to ground to supress it.

I think the resistor leads are a poorer antenna than the old copper wire. Fuzzy or something. Antenna science is a bit of a black art. If you take apart an aircraft spark plug shielded lead, you'll find that in many of them the core wire is a stainless, tightly-coiled spring, and I think that's to concentrate the magnetic field within the core so less of the signal escapes.



But besides that, the old cars had distributors with points and condensers, much like magnetos. They ran off the car's electrical system, meaning that as the points opened and closed thousands of times per minute, they created a pulsating flow in the primary circuit, pulsations that would run back through the wiring and ignition switch into the radios and other stuff, with the only protection being the battery and maybe an aftermarket suppressor, the sort of thing we used to add to our cars 50 years ago to get rid of radio and stereo noise. The battery has a very low resistance, a fraction of an ohm, and tends to shunt to ground the worst of the pulsation. The airplane's magneto has no such connection to the battery, so a lot more noise is released into the environment.

Modern cars have EFI run by computers that are full of suppression stuff. Not much noise. Still, get out in the middle of nowhere and try tuning in a far-off AM station and see what you hear. I know that most of you never drive into the middle of nowhere (like the Dakotas or Wyoming) and you live in cities awash in powerful station signals that drown out any ignition noise.