# Off Topic impossible



## GK1918 (Oct 11, 2013)

OT but is electrical.  I got a IH  TD15 Dozer probably one of the last that starts on gas then to diesel.  So the last time I forgot
to put a bucket over the muffler and some rain got in there. Then we got some water in the gas (holds about 1 gal.) ok still no start.
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.......

pic when it was yellow  not now


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## Ray C (Oct 11, 2013)

Glad he's OK.

... All it takes is a spark.


Ray


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## itsme_Bernie (Oct 11, 2013)

Maybe a carburetor bowl full of gas?  I can't imagine, unless gas was around the dozer from working on it?



Bernie


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## rgray (Oct 11, 2013)

If there was somehow power to the coil. I remember getting shocked a few times by points systems. If the points are in just the right spot, just about to open, and then the distributor is bumped or maybe a sticky centrifugal advance that then shifts (it's under spring pressure). And then it would have to have the rotor pointed at the cylinder being worked on 50/50 chance of that on a 2 cylinder. 
Not sure if a 2 cylinder starter motor would even have centrifugal advance.
Can't imagine a spark with out power to the coil.
Hard to imagine static making a spark.


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## DMS (Oct 11, 2013)

Could have just been static; dry air and a good walk across the shop is all it takes. Glad he's alright. Makes me glad we finally got a fire extinguisher for the shop.


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## fastback (Oct 11, 2013)

I also think that somehow the coil had a built up charge which released at the wrong time.  Obviously that cylinder had to be at TDC, but how did the points get power?  I'm sure you already checked out the wiring. Maybe a bad ignition switch that did not fully open the contacts.


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## DAN_IN_MN (Oct 11, 2013)

Glad your son is alright!  How old is he?

That is a weird one!  I hope he's not holding out on something he did!

The only way I can think of this happening is this.  The cylinder has gas in it.  The spark plug is laid by the spark plug hole connected to the spark plug wire.  Engine is turned over to visually check for spark.  Gas blows out of the hole, spark plug sparks igniting the gas.  

I lite my hands on fire with a snowmobile doing this.  Thankfully, I wasn't burned very bad.

The only way there can  be spark to a spark plug is if the points are closed to supply current to the primary windings of the coil.  When the points open, the power to the primary windings is cut off.  However, around those windings is something called EMF.  Electrical Magnetic Force.  The EMF collapses into the secondary winding and thus the spark you see at the plug.  All of that being said to say that unless there was a capacitor included in the circuit, I don't see where the current came from. 

OH,  I'd suggest a few flappers on the exhaust.  Such a cheap solution to a possible expensive problem.


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## Maxx (Oct 11, 2013)

Something doesn't add up.
I have the same type engine on my Farmall MD except mine has a magneto.
In my life I have never seen a spark created from installing a spark plug.
I have never seen anyone install a plug with the plug wire on.
Unless the starting lever was set to start mode the third valve is closed and the cup is isolated from the cylinder so gas could not be pushed out by the engine turning over.
There is no "storage" cap on the coil so unless the ignition is turned on there is no magnetic field for the points to control.
The only way I see for the gas tank to catch fire (at least on mine) is if it was leaking gas or if the cap was off and somehow the fumes ignited.

I'm glad your boy is alright but I suspect there is more to the story than what he told you.

The distributor cap is real close to the _carburetor so if the drain was leaking or he drained the bowl it would put gas in harms way for a loose spark from a disconnected plug wire if he bumped the engine over.
On mine the plugs are sparking even when in diesel mode IIRC.
_


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## jocat54 (Oct 12, 2013)

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.


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## Maxx (Oct 12, 2013)

jocat54 said:


> 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.


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## Ulma Doctor (Oct 13, 2013)

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)


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## rgray (Oct 14, 2013)

> 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.


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## DAN_IN_MN (Oct 14, 2013)

jocat54 said:


> 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.





Maxx said:


> 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?


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## Maxx (Oct 14, 2013)

DAN_IN_MN said:


> 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.


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## ray hampton (Oct 14, 2013)

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


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## Maxx (Oct 14, 2013)

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.


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## ray hampton (Oct 15, 2013)

Maxx said:


> 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.
> ...


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.


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## Maxx (Oct 15, 2013)

ray hampton said:


> 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.


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