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High Energy Ignition Coils

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At the weekend, I gave the engine a quick spray with the degreaser, left it a few minutes, then hosed it down.

Normally the engine starts up straight after this, as I am careful where I direct the hose nozzle.

Anyway, this time it didn't start, so off I go looking for the issue. 

Turned out in the end, to be water inside a supposedly "sealed" standard 30A automotive relay, I use to supply power to my high energy ignition coil, so the higher amperes, don't run through the ignition switch.

Anyway, replaced relay coil, & located it a bit higher up in the engine bay.

However, while checking things ignition, I lifted the dizzy cap, to see any water had ingress'd  in there.

Imagine my surprise, when i discovered there was no carbon button poking out of the centre of the cap.



Well there was, but there was not much left of it.  The Bakelite around the hole where the carbon sits was all broken away, as seen above.

Normally, a fault like this would cause all sorts of problems, but my engine had been working perfectly.

It then struck me, that because I have a hi-energy ignition coil capable of probably 40-50 Kilovolts; that when the carbon button worn down, it just continued to jump the small gap, & then eat the carbon button away. The gap between the top of the rotor button, & what's left of the carbon button, is around 4-5mm.

I had another 3K Denso dizzy cap, so grabbed it, & swapped it over.  Was just about to throw this above cap in the rubbish bin, when I had an idea.

If it will jump a gap that big, in atmospheric pressure, then why do I need a carbon button at all.  The cap was not reusable, because the centre hole was so broken away.   What if I put a solid metal rod down there that finished flush with the end of the hole.

A quarter inch gutter bolt was just the right size.  It was just a little too big in diameter, that it screwed nicely into the Bakelite dizzy cap. I then filed the thread end of the screw, so that when it touched the metal in the cap, at the bottom of the hole, the underside of the screw top, was flush with the end of the hole.  it was then just a matter of filing the domed head of the screw, so it was clear of the metal on the top of the rotor button.



So popped it back on the car; started up first pop, & took it for a drive, & it worked perfectly.

So it's back in the boot now, so if I'm ever caught again with a broken or worn rotor button, I'll just swap the cap over, & be on my way.

Reminded me of a story I once heard, that dirt track speed car guys, used to build a gadget with large plastic buttons, spacing the hi-tension leads on the cap, to produce an air gap outside the engine, that created a bigger spark across the spark plugs.

Don't know how true the story is, but my little experiment, indicated that you can certainly generate a  higher HV out of the coil, if the spark jumps a bigger gap, outside the combustion camber, before it jumps the spark plug gap.

Cheers  Banjo    



Edited by Banjo

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Love it!!  You're right, with three times the voltage you can jump three times the gap with electronic. No amps though, the spark is always a thin tiny bolt of lightning jumping a much larger plug gap.

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There is already an air gap at atmospheric pressure, between the ignition coil tower & the spark plug, even when the carbon button is "present".  It's the small gap between the tip if the dizzy rotor, & the four (4) pins in the dizzy cap.



i suppose you could grind or file away the end of rotor metal "finger", and create an air gap of some magnitude, if needs be.  However, the metal either side of the gap, really needs to be something hard, that will resist those billions of electrons burning & transferring metal to the other terminal.  You can see the buildup on the dizzy cap inner pins in the picture above.

I did notice on the rotor button, that was working, when there was no carbon button, in contact with it,  that there was already signs of metal movement away from the area, where the button, would normally rest, & create a round shiny area. (see pic below)



You can buy on ebay, a simple device for creating an adjustable air gap in your HT line from the coil tower.



  I've used one in the past to test a suspect coil.  You just turn the knurled knob, & make the "spark air gap", larger, until the coil cannot create a voltage high enough to "jump" the gap.  Those markings represent 20, 30, & 40kV.  the 40kV gap is about 20mm.

I've also used it, to adjust the dwell (time period the current flows in the coil primary winding), so that the coil just saturates, without wasting additional energy or heat, that won't improve the performance, of the coil, any further.

Cheers Banjo 


Edited by Banjo

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Further to this little episode early last year, the strangest thing happened last week.

Another Rollaclub member, Jamie, came around last week, to pick up a wiper motor for her KE25, that I'd fixed up some time ago.  We headed over to my messy garage to find it, & she was interested in the 5K on the test bed, with the "trigger wheel" & "COP" conversion.  I hadn't played it for a while, as other things had taken up my time, so when I went to start it, the battery was pretty flat.  After she had gone, I put the battery on charge, & later on in the afternoon, I took the charger off, as it was 100% full, & I decided to make sure it started.  It did not have the COP conversion on at the time, as I had been testing a new type of trigger "disk" with small rare earth magnets, acting as the teeth, being picked up, by a Hall Effect sensor.  I'd put the dizzy back temporarily.  The engine started & was sitting there idling OK,  I gave it a few quick revs, & out of the corner of my eye, something on the other side of the engine, was moving abnormally.  It was the distributor cap. I rev'd it again, & again the cap moved.  I then noticed, that I had removed the cap previously; probably to check where the rotor was pointing, & had just placed the cap back on loosely, & had not clipped the dissy cap down.  I could not believe what I was seeing; the cap had a gap of probably 10mm, between it & the dissy body, & it was bobbing around with no clips holding it in place at all; but the engine was running OK. All that was basically locating it was the ignition/spark plug leads. I rev'd it a couple more times, watched the cap jumping all over the place, & could not believe my eyes.  The gaps between the center of the rotor, & the carbon bush in the top of the cap, plus the gap between the end of the rotor, & the four spark plug lead contact points; must have been all over the place, but the engine ran perfectly, with just the slightest miss, every now & again. Stopped the engine, & fitted the cap properly, & put that down as a first: and a true indication, of how a spark can jump in free air, without causing the engine any issues.

Now I will admit, that the tower ignition coil that was in use, was a high energy type, with a possible HV output capacity of around 40 kVolts.  I might fit the little adjustable HV gap device pictured in the previous post, to the centre point on the dissy cap, & see what sort of gap, I can achieve, before it won't run.

Cheers Banjo


Edited by Banjo

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