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MG Midget and Sprite Technical - Ignitor and Spark Plug Wires

I have a side entry distributor cap with solid core plug wires and suppressor tips on my 1098 Mk II engine. I purchased these along with a pertronix Ignitor. I had a question about the resistance in the wire and was told that I needed to use a top entry cap and suppressor wires. The story goes that the suppressor tips were never a good idea in the first place and that the solid core wires produce radio frequency emissions that will damage the ignitor. Really? Is that true?

I want to keep the side entry cap because it fits well, the wires and cap look correct for the car (however this is not an authentic restoration, e.g. neg ground, alternator, etc.). I am not opposed to using alternative components, but I do want the car to look as original as practical.

I understand suppressor wires are built similar to a coax cable with shielding around the conductor to minimize RFI and that putting a pin through the shielding in a side entry cap negates the suppression. What I don’t understand is how suppressor tips are supposed to work. Can anyone explain the theory?

If I want to use the wires I have, is the only alternative to scrap the Ignitor and go back to points and condenser?


Paul Noeth

Not sure about the "do damage" scenario. It may be that the unsurpressed leads throw out rf signals which upset the trigger unit, maybe others will have better knowledge of this.
As for "having" to go back to points, I would have thought the LED/chopper triggered modules would not suffer this interference.
Allan Reeling

Allan, you are likely correct, I re-read the correspondence and the statement was "impact" the ignitor. "Damage" was my misinterpretation of what was said.
Paul Noeth

I've never found using unsupressed plug leads (wires) with an ignitor or any other electronic ignition system to cause a problem.
Daniel Stapleton

Paul,

I'm kind of guessing here, but isn't the purpose of the suppressor tips to provide resistance so as to produce a better spark? So, while they do that, they don't do any electric interference shielding. I think the suppressor wires do both jobs.

Also, I don't see why the pin in the cap through the suppressor wire would cause a problem. It seems that if it were a problem, the exposed metal of the rotor and cap contacts would have already caused the problem.

Charley
C R Huff


Engine bay looks rough. Get that sorted 1st.

Sorry - just a bit of bay envy.
G Rowles

Charley, I believe the problem with the shielded wires is that the pin in the side-entry distributor cap goes through the shielding and then into the core, connecting both together. The electrical energy can then be transmitted to the shielding negating the suppression. But, I am guessing here as well.

I did come across this statement on the magnecor site (http://www.magnecor.com/magnecor1/truth.htm) which mentions electronic ignition problems and damage.

<<SOLID CORE CONDUCTOR WIRES

Solid metal (copper, tin-plated copper and/or stainless steel) conductor wires are still used in racing on carbureted engines, but can cause all sorts of running problems if used on vehicles with electronic ignition, fuel injection and engine management systems, particularly if vehicle is driven on the street — and damage to some original equipment and modern aftermarket electronic ignition and engine management systems can occur. Solid metal conductor wires cannot be suppressed to overcome EMI or RFI without the addition of current-reducing resistors at both ends of wires.>>

G R, cut me some slack. I am aware of the condition of the engine bay, but please, this is my first attempt at resurrecting an old car. (Complement accepted. :)
Paul Noeth

I used (silicone?) shielded wires, and a top entry cap, when I first installed my Pertronix Ignitor, back in the mid '90s,and then, years later, I installed solid core "bumble bee" wire (because it looks really neat-o on an old British car) and used a side entry cap, and that, too, has worked fine for years and years.


No radio noise, or issues with the ignitor, from either set up, in my experience.


Norm

PS: beautiful engine bay, Paul, thanks for sharing that photo!
Norm Kerr

Opps...is that mustard on the valve cover...looks like someone been eatting lunch off the engine bay....hahaha

NICE !!!

An idea thats been rattling around in the ol hat holder...

How do able is it to install some metal studs or the top end of a spark plug into the cap where the spark plugs wires go, then add some spark plug boots to the wires

There have been so many times ive wanted to be able to quickly and easily remove the spark plug wire at the cap


On the surface it seems like a good idea, but considering ive never seen it done suggest its a bad idea...

Or maybe im a freaken genius for being the 1st to come up with this idea. :-)

Prop
Prop and the Blackhole Midget

I use Magnecor leads with an Ignitor and no problems.

Just read everyone comments about your engine bay and had a look - very clean. One comment is since the engine has an alternator rather than a dynamo why don't you fit the proper alternator bracket - surely it's small change to buy one?
Daniel Stapleton

the suppression is done by resistance, which is applied somewhere in the HT lead and is designed to reduce the current and slow the rise time of the HT pulse and reduce the transient emission spike created by that pulse.

On a standard midget with no radio there is no EMI benefit to suppressed leads or plugs. Everything is sufficiently immune. With a radio you might be able to hear it, and actually a modern engine *should* also be sufficiently immune to cope (immunity standards would suggest). Many modern engines have coil on plug arrangements to reduce the length of HT wire and therefore the EM emissions. The crank sensor wire is usually shielded anyway.

Magnecores stuff is heavily product biased, this statement

Solid metal conductor wires cannot be suppressed to overcome EMI or RFI without the addition of current-reducing resistors at both ends of wires

is just not true. But I've got a set on the V8 and they've reduced cross-firing over the old set drastically.

Regarding the ignitor, unsuppressed leads are unlikely to damage it (due to the greater (it's much closer) effect of arcing inside the distributor cap) but it might interfere with the signal. Simply twisting the two wires together (twisted pair) may well be enough to stop this interference, or careful cable layout if you want to be really sure, i.e. cross the HT leads @ right angles and avoid running parallel with them with the LV system.
Rob Armstrong

Hey rob

What does that loosly translate into english...hahaha

.
Prop and the Blackhole Midget

It'll probably be ok
Rob Armstrong

Norm, I agree the bumblebee wires look cool on a classic British sports car. Is there any advantage to them over what I have which is a 7mm Belden Metallic Cable? They are a solid core (actually stranded copper) wire. Are you using a suppressor tip? No radio noise? I am assuming this is on the FM band only. Who listens to AM anyway?

I am getting the impression that I will not damage the ignitor with solid core wires so I am not going to worry about it. If I run into performance issues then I'll take another look.

Rob, I don't understand what you mean by twisting the two wires together. Are you referring to the HT wires to the plugs or the two wires that come from the ignitor?

Prop, after reading many of your posts on this board there is no doubt in my mind that you are a freakin' genius. Your idea of putting spark plug terminals into a side-entry cap is awesome. Maybe no one has done it yet because it is so much easier to pull the leads off the plugs, pop the two clips that hold the cap, and walk the whole assembly over to the bench than it would be to MacGuyver the cap. Just thinkin' out loud that's all... maybe that's the reason? :)

Daniel, I didn't fit a proper alternator bracket because I didn't know one existed. Here all along I thought I was a freakin' genius for making the existing bracket work. (Actually, the idea came from a 'net article on alternator conversions.)
Paul Noeth

Hi,

no advantage at all, just looks :)

In an A Series, the Weslake designed head burns so well that pretty much any ignition system used, so long as it is fully up to snuff and sparks at the right time, will work as well as any other.


And, yes, I was surprised that I got no radio noise from the solid core wires, but the Sony radio (FM, Cassette or i-Pod, never once tried the AM) never gave me any trouble.


Paul, you are correct, our own Prop always takes the long way around.

Norm

Norm Kerr

Norm,

I hope I didn't offend Prop. My comment was very much tongue in cheek. In fact, I was thinking about how to put Prop's idea into action until it dawned on me that it would take hours of work to save a couple of minutes of time.

I have to give credit to Prop. He is always thinking of creative ways to solve a perceived problem and I like that. Some other time I will have to throw out my idea for a simple cruise control for the Midget. It's only slightly better than a broom stick jammed on the accelerator pedal but it is a unique solution for long drives.

And then there is my idea for a tiny swamp cooler to fit in line with the air duct tube. I would definitely do that if I lived in the desert, but I digress...
Paul Noeth

HT leads need to be separated as much as possible, LT wires from the ignitor can be twisted :)

If you're running suppressed plugs then radio noise is unlikely independent of the leads. Unsuppressed plugs and wires is more likely to interfere.
Rob Armstrong

Paul,

One advantage to your modified generator bracket is that you won't loose it like you might if you removed it.

Charley
C R Huff

yes paul,

Your such a bully, I still cant survive a night without crying....what you said was just so hurtful....I may well never drive a midget agian

I hope my pain brings you the pleasure you were seeking

LoL.

Prop



Prop and the Blackhole Midget

Charley, good point. I've made several changes, all in the pursuit of reliability and driveability. I've saved all of the original parts and everything I've done is reversible. But I have no idea why anyone would want to go back.

Prop, I know you can take some good natured ribbing, but after reading the recent story about the young school girl in Florida I wanted it to be clear what I said was all in fun. I can be a sarcastic mean-spirited SOB so I tried to show my sensitive side.

And yes, your pain does give me great pleasure!

Paul

Paul Noeth

I think one major benefit of shielded leads is to clear up the electronic signal when using a strobe light. Even with copper leads + Pertronix + A Plus tensioner on a duplex setup,I was still getting the 'appearance' of 3 or 4 degrees of spark scatter when timing in. This my rolling road guys advised me was all down to the copper leads with screw in caps creating unwanted electronic noise which upsets the strobe signal. Changing the copper wires with double silicon encapsulated leads instantly produced a rock steady reading.
F Pollock

This thread was discussed between 17/10/2013 and 19/10/2013

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