1/4 scale V8, first project.

[trumpy81]

Jeff, you are correct, but that is not sufficient to prevent the coil from firing. We are simply testing for operation of the coil which, depending upon the coil itself, should operate down to as little as 5v with a corresponding decrease in spark intensity. The absence of a capacitor affects this in no way, so the statement that it will not work without a capacitor is false.

 

[trumpy81]

Obviously Luc, you have never tried what I suggested. Please don't take my word for it, walk out to your car and try it yourself. Disconnect the coil completely from the vehicles wiring first then add your own wires to the positive and negative terminals of the battery and the coil. Touch the negative to and take it away from the battery terminal. It works doesn't it?

Nobody said anything about fine tuning, I merely suggested that Keith test the coils for operation, nothing more. Please read and understand what is written before making comments.

 

[steam58]

the coil worked for me then i did that

 

[trumpy81]

Thank you Steam58. It confirmed that the coil was working correct?

 

[keith5700]

Lakc, the insulator material in the plug is plain PTFE. The plug bore is 3.5mm and the centre electrode is 1mm, so that gives 1.25mm, or .050" of insulation inside the plug. I have wondered myself if the spark energy is going through the ptfe inside the plug, out of site.
I have had the ignition running in total darkness to try and spot any sparking/earthing problems, but have never seen anything.

It would certainly explain where the voltage is going, if it is earthing inside the plug, but doesn't really help with a solution, unless those machineable ceramics have a higher dielectric strength than ptfe. I'll have a look.
Cheers.

 

[stevehuckss396]

Alot of people here including myself have good luck with Corian counter top material. See if there is a cabinet shop near you that would be willing to give you a scrap piece of white.

 

[Lakc]

Macor does seem to be the material of choice but at $70+/foot for 1/4" I am not getting to play with it anytime soon.
If you have a timing light with an inductive pickup, or want to make an inductive pickup, it may tell you if the spark is actually going through the ignition wire or finding ground back inside the coil.

 

[keith5700]

Thanks Steve, I forgot about that stuff. I'll try and ebay a chunk.
Jeff, Thinking about it the timing light does go off when the spark dies. I need to try some different coils maybe?
My mate's coming round tonite with a Chevy HEi dizzy. Going to see if I can pirate that for bits.
Keith.

 

[t.l.a.r. eng]

Thinking about it the timing light does go off when the spark dies.

If using an induction type timing light, the light won't trigger for two reasons, either the secondary is grounded or there is no voltage output from the coil.

What happens when you shrink the plug gap to .015? Then under pressure?

What happens if you try a standard plug under pressure?

Having made plugs with questionable insulator materials, some fire inside and can't be seen. Work great on the bench, but they won't run the engine.

Electrical diagnosis is just a matter of process of elimination.

 

[user 2584]

Just on a side note,
PTFE dielectric constant 2.1
Sintered Alumina dielectric constant 10

Sintered Alumina is usually the insulator material for spark plugs.

 

[keith5700]

Thanks for replies. It all gets absorbed into the brain-box, even if I forget to reply to specific points.
I certainly will try the standard plug under pressure, when I can sort a suitable tap out.
My current thinking is that the coils are crap. They were no-name ones of ebay, a bit cheaper than the Powerspark ones.

I have the Chevy distributor and will be stripping it tonite to see if I can cobble it to the front of the engine.

I've scrounged a smaller carb. Will put a pic up tonite for comments.

Bynne, my research shows ptfe to be about 30% more insulating than sintered alumina, rather than 5 x worse.
Everybody seems to use different units but I suspect if alumina constant is 10, as you said, then ptfe will be 21?

Cheers, Keith.

 

[Lakc]

Bynne, my research shows ptfe to be about 30% more insulating than sintered alumina, rather than 5 x worse.
Everybody seems to use different units but I suspect if alumina constant is 10, as you said, then ptfe will be 21?

Cheers, Keith.

I looked that up too, and the answer seems to be "it depends". Plain PTFE lists at 600-2000v/.001", glass filled PTFE 330-600, and Roulon 100-1100. I found an even wider range for porcelains.

 

[user 2584]

Ah now I see, we are talking about different things. I was talking about dielectric constant, which has meaning on terms of capacitivity. The other is dielectric strength, which has meaning in terms of insulation breakdown (arcs).
There ptfe seems to be better than alumina. Perhaps the problem with the powerspark is the capacitance of the plug?

 

[keith5700]

Well, it seems there's nothing wrong with the plugs. I wired the Chevy dizzy up and tested my plug. It showed a really fat spark.

So then I put the plug in the pressure tester and wound the pressure up.Got up to full pressure with still a nice fat spark.

This is the guts of the sender unit. The plan is to get the trigger wheel and outer magnet (reluctor?) on the flywheel and then have another go at firing the engine.

Back in a few days....

 

[keith5700]

Yes, good point. I'll file 4 of the points off the ring and the inner wheel, not shown in pic. Cheers.

 

[Lakc]

Thats the factory GM module, you can lick one finger and put it on the battery positive and touch your other hand to one of the reluctor terminals and it will spark. For a good test you can just move an electric engraver next to the reluctor coil and it should spark all day. If you do decide to do some heavy testing with that module. you need to have it mounted with heatsink compound as it sinks from the bottom.

Thats one of the first generation electronic ignitions, and one of the best ever made. It only needs 5 connections, B+, ground, negative side of the coil, and both sides of the pulse generator (reluctor). It takes about a volt and a half to trigger, and only pays attention to the positive pulse, so you can literally run it off a hall sensor if you like.

When a coil misfires or arcs internally because of too high external resistance it will start to carbonize the materials it jumps across. This carbon tracking will eventually look like a short to a spark and of course it takes the easiest way to ground. Your ebay coils were probably half shot through, and when they needed to fire under load the existing carbon tracking was an easier path.

 

[stevehuckss396]

Check amazon for coils. Someone was dumping coils brand new in the box about 3 weeks ago. I needed a duel coil and scored one for 35 dollars. They are mostly for single and 2 cylinder snowmobiles and wave runners from the early 80's and 90's. Most likely someone clearing the shelfs at a dealer or repair shop.

 

[keith5700]

Thanks all. Some good points raised. Funnily enough I was lying in bed last night after saying I'd file off 4 of the pointy things and thought 'hang on a minute, that might not produce enough voltage'.
Then I thought even if it did work, how am I going to split the sparks between 2 x dizzys.

My conclusion at the time was to keep all 8 points and feed both dizzys with 8 sparks per rev. Hopefully the spark would then take the easiest route, which would be whichever of the 2 rotor arms was in line with a cap contact at the time. I think I'll call this invention 'wasted spark!'

Then I wondered if I could junk all the GM trigger magnet stuff and just trigger the module with something else, as has been suggested above.
I have a GM crank trigger somewhere so I'll give that a whirl tonite.
Mounting the GM stuff on the flywheel means I won't be able to get my starter on it in it's present form.

Jeff, the 2 x coils I have are new. Might be Chinese copies though.

Cheers.

 

[sandman]

so one question i have is are you planing on having 2 cylinders fire at once, since you have 2 dizzys, or are they off-set? if you are going to supply 8 pulses to both dizzys at the same time then you are going to get firing in between the terminals, in that case the spark might jump to the closest terminal and might fire the cylinder wile it is on the wrong stroke, which would lead to backfiring out the exhaust or the carb. maybe im wrong but thats what i forsee.

 

[t.l.a.r. eng]

As the GM pole piece is nothing more than a coil of wire around an armature with a poled magnet running inside, why not just use four magnets in the flywheel and a small coil of wire for the pickup?
This could make it a simple crank trigger system, and the pickup coil could be slotted for timing adjustments. The GM ignition module has an advance curve built into it but that is a whole new subject.