Off Topic impossible

[Ulma Doctor]

my kid pulled the plugs and I sand blasted them. He put a new 12vt coil. Then I went back to the shop. Next thing I know my kid
comes running all burnt up for a extinguisher. Well he's alright just singed up a little, dozer was yellow now its black. Kid said no 2
cyl exploded when he started threading the spark plug in thus catching the gas tank fire.
The impossible question HOW? Engine is coil points system not "magneto"- Ign Off, Kill switch off, gas shut off valve off.
weather around 60* grass kind of due'ey (wet) , the kid dont smoke.
so dont the weather rule out static charge from his fingers. He allready put one plug in, it was cyl 2 that blew right at him. He is sitting
on a steel track, so his butts grounded.
One for the books tottally impossible. Just can - not happen. And my kids a DFD fireman, been to fire academy knows about high tension
line fires and such.
any thoughts gentlemen.......

HI,
I have a possibility to interject.
you said you sand blasted the plugs, a lot of static electricity is built up when sandblasting.
it could have been that the spark plug held the static electricity charge and when inserted into the hole the static jumped the gap to ground.
you made no mention of the spark plug wire being attached to the plug when the fire occurred, so, i'll make the assumption it was not there. most times the plug is installed, then the plug wire is installed.
if my assumption is correct this would not indicate any fault in the ignition system because it was not actually hooked up to deliver any spark from the ignition coil.

some spark plug sockets have a piece of rubber that cushions the spark plug and fix it's alignment in the socket when tightening. rubber is an excellent insulator of static electricity as well.
that fact brought me to the conclusion offered, by no means the only possibility...
but one of high plausibility

if there are more facts available, i'd be happy to go deeper into the mystery.
mike)

 

[rgray]

The condenser in a points and condenser system holds a good charge.

Much horseplay in the shops I have worked in by charging up a condenser and tossing it someone to catch---it will shock the heck out of you.

We used to do that way back when in high school.
We would charge the little condenser with a spark off the ignition coil....35,000 to 45,000 volts I suppose.
Gives quite a zap to the unsuspecting person that picks it up next.

 

[DAN_IN_MN]

The condenser in a points and condenser system holds a good charge.

Much horseplay in the shops I have worked in by charging up a condenser and tossing it someone to catch---it will shock the heck out of you.

I'll have to disagree.
The condenser is only about 0.2uF and it is there to keep the points from burning from PIV and the help with a touch of resonance of the coil.
At 0.2uf you can charge it to 12v and hook it up to a coil and it will not be able to charge the coil from lack of current storage capacity.
Unless you have thin skin or a cut you won't get electrocuted from 12v.
Whatever condensers were being thrown around were charged way higher than 12v.

I guess it's time to set up a small experiment.

I'm going to take a condenser, and coil to see what the output will be with the discharge of the condenser/capacitor into an ignition coil.

OP, did you get the cat running again?

 

[Maxx]

I guess it's time to set up a small experiment.

I'm going to take a condenser, and coil to see what the output will be with the discharge of the condenser/capacitor into an ignition coil.

OP, did you get the cat running again?

Dan, if you do also try it with a 1,000uf and higher to see if it will fire a spark.
I'm fairly confident that 50,000-100,000uf will do it.
That is if you have the parts, I do here but lack of time for the next few weeks due to harvest time.

 

[ray hampton]

12 volts will not kill you unless your skin are WET, think how many people get zap by the spark plug voltage [10000 volts ] the amps are what kill a fellow, if the cap.are charged and are discharged thru. the coil then the spark could explode the gasoline

 

[Maxx]

They say a picture is worth a thousand words.
If there is 12v on the condenser that means there is no ground for the condenser to discharge to.
The condenser is in parallel with the points that supply ground to the coil.
The spark is produced when the field collapses and that is when the points are open.
The capacitor can not fire the coil.
If you take a large condenser (capacitor) and charged it up and put it across the positive and negative terminals of the coil it will produce a spark when the voltage collapses from the coil sucking up all the current.

 

[ray hampton]

They say a picture is worth a thousand words.
If there is 12v on the condenser that means there is no ground for the condenser to discharge to.
The condenser is in parallel with the points that supply ground to the coil.
The spark is produced when the field collapses and that is when the points are open.
The capacitor can not fire the coil.
If you take a large condenser (capacitor) and charged it up and put it across the positive and negative terminals of the coil it will produce a spark when the voltage collapses from the coil sucking up all the current.

View attachment 62251

If my memory serve me right your coil starts with 12 volts and steps it UP to 20000 volts, when this happen you will attain a new charge of 250 volts, is this charge from the cap.

 

[Maxx]

If my memory serve me right your coil starts with 12 volts and steps it UP to 20000 volts, when this happen you will attain a new charge of 250 volts, is this charge from the cap.

It's been a few decades since I scoped out a points ignition so I don't recall the voltage that rings across the capacitor but IIRC that higher voltage is AC not DC and a condenser (capacitor) can not store an AC voltage so it bounces it back.
The condenser absorbs the peak inverse voltage caused by the collapsing magnetic field to help keep the points from burning.
It also sets up an LC circuit with the coil that forms a resonant circuit to help create a better spark.