Home » Public Forums » GMCnet » [GMCnet] How to heat up the Onan ignition?
| [GMCnet] How to heat up the Onan ignition? [message #194029] |
Wed, 26 December 2012 09:00  |
Robin Hood
Messages: 1078
Registered: April 2011
Karma: 3
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Well, I've got the Onan back together after decarbonizing the heads
and cylinders, oil change, etc. The intake and exhaust manifods are
painted smurf blue and high temp black, respectively.
it's refusing to start. It coughed a couple of times, and that was it.
I run my battery down trying to get it started. It hasn't even coughed
since.
It was working fine(ish) for a while before I took it apart.
To me, the symptoms are screaming "ignition." The carb is working, as
evidenced by the fact that it's so cold that condensation was forming
on it, yesterday, indicating a phase change from liquid to gas. Air
isn't a problem. As an aside, my electric choke works now that I've
taken stuff apart and cleaned it up and put it back together.
I sprayed the spark plugs with carb cleaner and wiped 'em off with a
paper towel. They're pretty much new, and don't look particularly
fouled. I've heard that there's a way to look at the end of a spark
plug and it tells you something about the conditions under which it
runs (rich or lean, temperature, something like that) but I'm not to
that point in my mechanical education yet, it seems. The plugs are
properly gapped.
So, I see that from a timing perspective, the Pertronix upgrade helps
with a consistently timed spark... but it's a weak spark. Also, I'm
given to understand that the Onan's spark is pretty weak, since it
fires both plugs whether a particular cylinder needs it or not,
halving the "oomph" available to make the fuel/air mixture go "Bang".
Is there a way to get a more powerful spark into the Onan's spark
plugs? Is there a different coil that will help? If it's worth doing,
it's worth overdoing. :) The thing is out of my coach right now, and I
may as well do as much to it as I can while it's easy, right?
--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194033 is a reply to message #194029] |
Wed, 26 December 2012 09:30  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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There are ways, but when the box stock ignition is working, it works just fine. So, let's figure out why it (apparently) ain't working. While the battery charges, take BOTH plugs out. Set them where you can see the electrodes, and ground both with clip cords. Don't know what a clip-cord is? Visit Radio Shack, and get a couple packs of them, they're priceless. (Your clients may well know them as 'Ropach Clips". Don't ask them).
With a hot battery and the plugs outm, the starter will sping the engine at dam' near running speed. Both sparking plugs should show lots o fire while spinning. Nice blue spark from center electrode to the side one. I(f they don't, find out why, normal troubleshooting is in order. Soon as you have fire, take a look at timing which ought to be someplace slose to the top of each piston's travel. Get it to this point, stuff the plugs back where they belong, give it a shot of gas down the carb, and spin it up. It should at least run on the prime for a bit. If that's all it does, find out why there ain't any gas out of the cabr and fix it.
I'm betting that along the way, you got something on the plugs which has shorted them. The above test will tell. If they don't spark... or if you're cheeeep like me, take each one and burn it off with a propane torch at the firing end. Then try again. No sparks at all, heal till there are.
--johnny
From: Robin Hood <loxley@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, December 26, 2012 10:00 AM
Subject: [GMCnet] How to heat up the Onan ignition?
Well, I've got the Onan back together after decarbonizing the heads
and cylinders, oil change, etc. The intake and exhaust manifods are
painted smurf blue and high temp black, respectively.
it's refusing to start. It coughed a couple of times, and that was it.
I run my battery down trying to get it started. It hasn't even coughed
since.
It was working fine(ish) for a while before I took it apart.
To me, the symptoms are screaming "ignition." The carb is working, as
evidenced by the fact that it's so cold that condensation was forming
on it, yesterday, indicating a phase change from liquid to gas. Air
isn't a problem. As an aside, my electric choke works now that I've
taken stuff apart and cleaned it up and put it back together.
I sprayed the spark plugs with carb cleaner and wiped 'em off with a
paper towel. They're pretty much new, and don't look particularly
fouled. I've heard that there's a way to look at the end of a spark
plug and it tells you something about the conditions under which it
runs (rich or lean, temperature, something like that) but I'm not to
that point in my mechanical education yet, it seems. The plugs are
properly gapped.
So, I see that from a timing perspective, the Pertronix upgrade helps
with a consistently timed spark... but it's a weak spark. Also, I'm
given to understand that the Onan's spark is pretty weak, since it
fires both plugs whether a particular cylinder needs it or not,
halving the "oomph" available to make the fuel/air mixture go "Bang".
Is there a way to get a more powerful spark into the Onan's spark
plugs? Is there a different coil that will help? If it's worth doing,
it's worth overdoing. :) The thing is out of my coach right now, and I
may as well do as much to it as I can while it's easy, right?
--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194034 is a reply to message #194033] |
Wed, 26 December 2012 09:44 |
Robin Hood
Messages: 1078
Registered: April 2011
Karma: 3
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Ok, that will be tonight's video then. :)
On Wed, Dec 26, 2012 at 9:30 AM, Johnny Bridges <jhbridges@ymail.com> wrote:
> There are ways, but when the box stock ignition is working, it works just fine. So, let's figure out why it (apparently) ain't working. While the battery charges, take BOTH plugs out. Set them where you can see the electrodes, and ground both with clip cords. Don't know what a clip-cord is? Visit Radio Shack, and get a couple packs of them, they're priceless. (Your clients may well know them as 'Ropach Clips". Don't ask them).
> With a hot battery and the plugs outm, the starter will sping the engine at dam' near running speed. Both sparking plugs should show lots o fire while spinning. Nice blue spark from center electrode to the side one. I(f they don't, find out why, normal troubleshooting is in order. Soon as you have fire, take a look at timing which ought to be someplace slose to the top of each piston's travel. Get it to this point, stuff the plugs back where they belong, give it a shot of gas down the carb, and spin it up. It should at least run on the prime for a bit. If that's all it does, find out why there ain't any gas out of the cabr and fix it.
> I'm betting that along the way, you got something on the plugs which has shorted them. The above test will tell. If they don't spark... or if you're cheeeep like me, take each one and burn it off with a propane torch at the firing end. Then try again. No sparks at all, heal till there are.
>
> --johnny
>
> From: Robin Hood <loxley@gmail.com>
> To: gmclist@temp.gmcnet.org
> Sent: Wednesday, December 26, 2012 10:00 AM
> Subject: [GMCnet] How to heat up the Onan ignition?
>
> Well, I've got the Onan back together after decarbonizing the heads
> and cylinders, oil change, etc. The intake and exhaust manifods are
> painted smurf blue and high temp black, respectively.
>
> it's refusing to start. It coughed a couple of times, and that was it.
> I run my battery down trying to get it started. It hasn't even coughed
> since.
>
> It was working fine(ish) for a while before I took it apart.
>
> To me, the symptoms are screaming "ignition." The carb is working, as
> evidenced by the fact that it's so cold that condensation was forming
> on it, yesterday, indicating a phase change from liquid to gas. Air
> isn't a problem. As an aside, my electric choke works now that I've
> taken stuff apart and cleaned it up and put it back together.
>
> I sprayed the spark plugs with carb cleaner and wiped 'em off with a
> paper towel. They're pretty much new, and don't look particularly
> fouled. I've heard that there's a way to look at the end of a spark
> plug and it tells you something about the conditions under which it
> runs (rich or lean, temperature, something like that) but I'm not to
> that point in my mechanical education yet, it seems. The plugs are
> properly gapped.
>
> So, I see that from a timing perspective, the Pertronix upgrade helps
> with a consistently timed spark... but it's a weak spark. Also, I'm
> given to understand that the Onan's spark is pretty weak, since it
> fires both plugs whether a particular cylinder needs it or not,
> halving the "oomph" available to make the fuel/air mixture go "Bang".
>
> Is there a way to get a more powerful spark into the Onan's spark
> plugs? Is there a different coil that will help? If it's worth doing,
> it's worth overdoing. :) The thing is out of my coach right now, and I
> may as well do as much to it as I can while it's easy, right?
>
> --
> Robin Hood
> Jackson, MS
> 2003 Buick Lesabre
> 1968 Pontiac Catalina
> 1978 GMC Royale motorhome
> 1977 GMC Palm Beach motorhome
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194036 is a reply to message #194034] |
Wed, 26 December 2012 10:06 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Robin,
In my experience, the Onan spark is so weak it's almost invisible with
significant ambient light. A Harbor Freight spark tester (a plastic
housing containing a light bulb, with spark plug in- and out-put connectors
-- $2.99) is invaluable for that and other ignition tests.
Ken H.
On Wed, Dec 26, 2012 at 10:44 AM, Robin Hood <loxley@gmail.com> wrote:
> Ok, that will be tonight's video then. :)
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194038 is a reply to message #194036] |
Wed, 26 December 2012 10:14 |
Robin Hood
Messages: 1078
Registered: April 2011
Karma: 3
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Senior Member |
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I do have a spark tester... it's a little plastic doodad. Black
plastic on three sides, with one side open. You adjust the gap by
turning a screw, and look to see if there's a spark in there
somewhere. I'll be sure to do this test with the garage door down and
the lights off. And no alcohol. :) I don't have a problem, really. No,
it's not denial. :) Ferpetesakes, you shoot ONE slightly tipsy
video...
On Wed, Dec 26, 2012 at 10:06 AM, Ken Henderson <hend4800@bellsouth.net> wrote:
> Robin,
>
> In my experience, the Onan spark is so weak it's almost invisible with
> significant ambient light. A Harbor Freight spark tester (a plastic
> housing containing a light bulb, with spark plug in- and out-put connectors
> -- $2.99) is invaluable for that and other ignition tests.
>
> Ken H.
>
> On Wed, Dec 26, 2012 at 10:44 AM, Robin Hood <loxley@gmail.com> wrote:
>
>> Ok, that will be tonight's video then. :)
>>
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194058 is a reply to message #194036] |
Wed, 26 December 2012 14:12 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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If necessary, shade with your hand or a paper sack between the plug and the overhead light. There should be sufficient spark to see. I've not used the HF tester. I have used one which consisted of a neon bulb which would flash - albeit dimly - with a carboned plug that would not fire. Consequently, I don't trust one till I've seen it work. If your plugs are fouled enough to provide a high resistance short to ground, the light may well flash even though no spark goes across the gap. I realize it's a PIA to pull them and look... but when I see a spark across the electrodes, I know the dam' thing is firing.
--johnny
'76 23;' transmode norris
'76 palm beach
From: Ken Henderson <hend4800@bellsouth.net>
To: gmclist <gmclist@temp.gmcnet.org>
Sent: Wednesday, December 26, 2012 11:06 AM
Subject: Re: [GMCnet] How to heat up the Onan ignition?
Robin,
In my experience, the Onan spark is so weak it's almost invisible with
significant ambient light. A Harbor Freight spark tester (a plastic
housing containing a light bulb, with spark plug in- and out-put connectors
-- $2.99) is invaluable for that and other ignition tests.
Ken H.
On Wed, Dec 26, 2012 at 10:44 AM, Robin Hood <loxley@gmail.com> wrote:
> Ok, that will be tonight's video then. :)
>
>
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
|
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194080 is a reply to message #194029] |
Wed, 26 December 2012 20:32 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Now that your choke is "working" is it just flooded? Hold the choke open and crank. Wet plugs, cold weather, and weak spark are a bad combination. Also plug gap is I think .020 NOT .035 like most things.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194088 is a reply to message #194080] |
Thu, 27 December 2012 03:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| JohnL455 wrote on Wed, 26 December 2012 20:32 |
Now that your choke is "working" is it just flooded? Hold the choke open and crank. Wet plugs, cold weather, and weak spark are a bad combination. Also plug gap is I think .020 NOT .035 like most things.
|
I would have to look it up again but I think the plug gap is .016."
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194126 is a reply to message #194029] |
Thu, 27 December 2012 07:46 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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If you cleaned the plugs with a wire brush, you probably rendered the
electrodes useless. Those things like sharp edges. Use a needle file on
them.
One whisker out of time really jams up a Pertronix unit and will also
cause the problems you describe. However, once you get it perfect, you
never have to deal with it again.
On Wed, Dec 26, 2012 at 8:00 AM, Robin Hood <loxley@gmail.com> wrote:
> Well, I've got the Onan back together after decarbonizing the heads
> and cylinders, oil change, etc. The intake and exhaust manifods are
> painted smurf blue and high temp black, respectively.
>
> it's refusing to start. It coughed a couple of times, and that was it.
> I run my battery down trying to get it started. It hasn't even coughed
> since.
>
> It was working fine(ish) for a while before I took it apart.
>
> To me, the symptoms are screaming "ignition." The carb is working, as
> evidenced by the fact that it's so cold that condensation was forming
> on it, yesterday, indicating a phase change from liquid to gas. Air
> isn't a problem. As an aside, my electric choke works now that I've
> taken stuff apart and cleaned it up and put it back together.
>
> I sprayed the spark plugs with carb cleaner and wiped 'em off with a
> paper towel. They're pretty much new, and don't look particularly
> fouled. I've heard that there's a way to look at the end of a spark
> plug and it tells you something about the conditions under which it
> runs (rich or lean, temperature, something like that) but I'm not to
> that point in my mechanical education yet, it seems. The plugs are
> properly gapped.
>
> So, I see that from a timing perspective, the Pertronix upgrade helps
> with a consistently timed spark... but it's a weak spark. Also, I'm
> given to understand that the Onan's spark is pretty weak, since it
> fires both plugs whether a particular cylinder needs it or not,
> halving the "oomph" available to make the fuel/air mixture go "Bang".
>
> Is there a way to get a more powerful spark into the Onan's spark
> plugs? Is there a different coil that will help? If it's worth doing,
> it's worth overdoing. :) The thing is out of my coach right now, and I
> may as well do as much to it as I can while it's easy, right?
>
> --
> Robin Hood
> Jackson, MS
> 2003 Buick Lesabre
> 1968 Pontiac Catalina
> 1978 GMC Royale motorhome
> 1977 GMC Palm Beach motorhome
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Take care,
Steve
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194142 is a reply to message #194131] |
Thu, 27 December 2012 20:00 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Chuck / Robin,
Here's one at J&P cycles for a couple bucks less:
http://www.jpcycles.com/product/3000140
Regards,
Rob M.
PS - Robin wants to make the Onan mo betta lookin' so this chrome coil will help with that! ;-)
-----Original Message-----
From: Charles Boyd
Sir: I don`t know the numbers but the motorcycle coil will fire a .35 gap at wot. I think it will work in stock location if you
remove the bracket. These use to be available in black for about $25, Can`t find them anymore, but still looking.
http://customchromecatalog.com/2012/full.asp?page=258
Is there a way to get a more powerful spark into the Onan's spark
plugs? Is there a different coil that will help? If it's worth doing,
it's worth overdoing. :) The thing is out of my coach right now, and I
may as well do as much to it as I can while it's easy, right?
Robin
--
C. Boyd
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194164 is a reply to message #194029] |
Thu, 27 December 2012 21:47 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Trying to get a higher voltage across a spark plug(s) using a points ignition is very difficult. The limiting factor is the points itself. The points are the switching device and can only carry a given amount of current. If the points are forced to move more than their designed load the points surface burns away while opening an closing.
The easiest way for me to explain it is to say that the coil is nothing more that a transformer with two sides. One side, in the case of the onan, is 12 volts and the other side is high voltage going to the spark plugs. You can not get more power out on the secondary side than you put in on the primary (12 volt) side. Power is volts multiplied by amps. Let use some simple numbers.
On the input lets say you have 12 volts and the points will carry 2.0 amps maximum. That means you have 2 amps X 12 volts or 24 watts input available for input. On the output side lets say you have 2400 volts jumping the plugs.
So on the output you have 2400 volts times ? amps which equals 24 watts. The question ? in this case would be .01 amps.
This means the example coil is wound at a 200 to 1 ratio. (12 volts in and 2400 volts out)
So if you want to increase the secondary voltage output you would have to wind a different coil that will take more current on the input side. Say 300 to 1 or 400 to 1.
The table looks like this
200 to 1 is 12 volts X 2 amps for 2400 volts out - 24 watts used
300 to 1 is 12 volts x 3 amps for 3600 volts out - 36 watts used
400 to 1 is 12 volts x 4 amps for 4800 volts out - 48 watts used
500 to 1 is 12 volts x 5 amps for 6000 volts out - 60 watts used
There is really more to it because the wattage and secondary amperage also goes up with the secondary voltage but for this explanation just go with the above numbers.
So to go to a higher spark plug voltage you need to replace the limiting factor with a something other than points. That is where transistorized switching comes in. Back in the early 70's that is what we did to increase performance with aftermarket products the the Delta Products unit. Later GM did the same thing with the HEI ignition. I also assume that the Pertronix unit would do the same thing but I do not know what it's current switching ability is. You would have to call them to see what their current switching spec is.
Keep in mind that the ONAN normally uses a lower ratio coil and no ignition resistor. Most automotive applications used a higher ratio coil with an ignition resistor. This allowed them to jumper out the resistor during starting and then revert to a lower input voltage while running to prevent points from burning.
Maybe someone else can explain it simply that I did.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194167 is a reply to message #194164] |
Thu, 27 December 2012 21:57 |
Robin Hood
Messages: 1078
Registered: April 2011
Karma: 3
|
Senior Member |
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I know Ohms law, if it helps. I had a physics professor once, said we
could use a notecard with useful formulas on our exam. "But really,
F=MA, and you can't push on a rope. You can just derive the rest" is
what he would say. :)
Dunno if y'all saw, but apparently one of my plug wires is bad. It
WASN'T bad before, but it's bad now. No continuity. The other one has
continuity, resstance of around 1500 ohms. I'm not sure what's caused
this. It was working fine, dangit.
On Thu, Dec 27, 2012 at 9:47 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Trying to get a higher voltage across a spark plug(s) using a points ignition is very difficult. The limiting factor is the points itself. The points are the switching device and can only carry a given amount of current. If the points are forced to move more than their designed load the points surface burns away while opening an closing.
>
> The easiest way for me to explain it is to say that the coil is nothing more that a transformer with two sides. One side, in the case of the onan, is 12 volts and the other side is high voltage going to the spark plugs. You can not get more power out on the secondary side than you put in on the primary (12 volt) side. Power is volts multiplied by amps. Let use some simple numbers.
>
> On the input lets say you have 12 volts and the points will carry 2.0 amps maximum. That means you have 2 amps X 12 volts or 24 watts input available for input. On the output side lets say you have 2400 volts jumping the plugs.
>
> So on the output you have 2400 volts times ? amps which equals 24 watts. The question ? in this case would be .01 amps.
>
> This means the example coil is wound at a 200 to 1 ratio. (12 volts in and 2400 volts out)
>
> So if you want to increase the secondary voltage output you would have to wind a different coil that will take more current on the input side. Say 300 to 1 or 400 to 1.
>
> The table looks like this
>
> 200 to 1 is 12 volts X 2 amps for 2400 volts out - 24 watts used
> 300 to 1 is 12 volts x 3 amps for 3600 volts out - 36 watts used
> 400 to 1 is 12 volts x 4 amps for 4800 volts out - 48 watts used
> 500 to 1 is 12 volts x 5 amps for 6000 volts out - 60 watts used
>
> There is really more to it because the wattage and secondary amperage also goes up with the secondary voltage but for this explanation just go with the above numbers.
>
> So to go to a higher spark plug voltage you need to replace the limiting factor with a something other than points. That is where transistorized switching comes in. Back in the early 70's that is what we did to increase performance with aftermarket products the the Delta Products unit. Later GM did the same thing with the HEI ignition. I also assume that the Pertronix unit would do the same thing but I do not know what it's current switching ability is. You would have to call them to see what their current switching spec is.
>
> Keep in mind that the ONAN normally uses a lower ratio coil and no ignition resistor. Most automotive applications used a higher ratio coil with an ignition resistor. This allowed them to jumper out the resistor during starting and then revert to a lower input voltage while running to prevent points from burning.
>
> Maybe someone else can explain it simply that I did.
>
> Ken B.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
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Robin Hood
Jackson, MS
2003 Buick Lesabre
1968 Pontiac Catalina
1978 GMC Royale motorhome
1977 GMC Palm Beach motorhome
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194168 is a reply to message #194162] |
Thu, 27 December 2012 22:03 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Robin,
Think those result through: There's only one secondary winding in your
ignition coil. There's a plug wire attached to each end of that winding.
You attached your spark tester to the far end of each of those wires -- in
effect, you attached it to each end of a SINGLE wire (ignoring the two
connections at the coil). The only way there can be current conducted
through the spark tester is for the circuit to be grounded somewhere on the
OPPOSITE side of the coil. If you're certain of the infinite impedance of
that far wire, then there must be a short to ground either inside the
coil, near the far output terminal, or immediately around it. That should
narrow your search significantly. Start by checking the resistance between
each of the secondary terminals and the case; then between the primary and
secondary terminals.
It's possible that the open plug lead forced the secondary voltage to arc
across the output terminal and form a carbon arc, so examine the coil
carefully.
No, there's nothing special about the plug wires themselves. You may find
the high impedance is only due to a loose terminal. IIRC, the coil end
terminal is nothing but a washer through which the wire is threaded and
then splayed out before the nut is screwed into the coil tower.
HTH,
Ken H.
On Wed, Dec 26, 2012 at 9:00 PM, Robin Hood wrote:
> Well, bollocks.
>
> I get sparks visible in my spark plug tester from one wire (which read 1500
> ohms) but not the other (which read as infinite resistance). Dangit, the
> thing WAS working! I have proof!
>
> So I have a bad wire? I mean, it certainly looks that way. Are these
> "special" in some way plug wires?
>
>
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194172 is a reply to message #194167] |
Thu, 27 December 2012 23:06 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Robin Hood wrote on Thu, 27 December 2012 21:57 |
I know Ohms law, if it helps. I had a physics professor once, said we
could use a notecard with useful formulas on our exam. "But really,
F=MA, and you can't push on a rope. You can just derive the rest" is
what he would say. 
Dunno if y'all saw, but apparently one of my plug wires is bad. It
WASN'T bad before, but it's bad now. No continuity. The other one has
continuity, resistance of around 1500 ohms. I'm not sure what's caused
this. It was working fine, dangit.
|
I believe those are the graphite or something like that on cotton center core wires. They should read 1000 to 4000 ohms depending on their length. Usually if one opens up, the problem is one of the connectors on the ends of the wire. I have in the past taken a paper clip and stuck it in the center of the wire and folded it over the end and then replaced the crimped on terminal. You can also just shorten the wire about 1/2 inch and re-crimp the terminal on the wire. Those resistance wires are for ignition noise reduction in your radio. You can use solid copper wires if you have one around.
Since those plugs are wired in series, one bad wire will prevent both plugs from firing. On an Onan I usually pull both plug wires and ohm meter between both plug wires on the spark plug ends. This checks the circuit of both wires and the secondary of the coil all at one time. If that reads under 6,000 or 7,000 ohms you are good to go. Of course if it reads open then you will have to meter each piece individually (spark plug wires and secondary of the coil) to find out where the circuit is open.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194174 is a reply to message #194173] |
Thu, 27 December 2012 23:22 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| LarryInSanDiego wrote on Thu, 27 December 2012 23:17 |
Interesting, I never looked at it that way. So I guess that means anything that has waste spark can be tested that way? What a time saver! (slaps forehead)
|
Larry I'm not 100% sure that all wasted spark ignitions work this way. I know the Onan does. If the engine has a single coil for 2 cylinders then it works this way.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194193 is a reply to message #194162] |
Fri, 28 December 2012 07:20 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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You get spark from one wire, the other end of the coil is grounded someplace. If the non-sparking wire reads infinite, then it ain't connected someplace. Check for continuity across the coil where the plg wires connect. Then check each end to ground. You should get the continuity ~1500 or so between the two, and infinite to ground. Non infinite to ground, a short in the coil. Open wire, find and replace. You are becoming the go-to guy for Onans!
--johnny
'76 23' transmode norris
'76 palm beach
From: Robin Hood <loxley@gmail.com>
To: "gmclist@temp.gmcnet.org" <gmclist@temp.gmcnet.org>
Sent: Wednesday, December 26, 2012 9:00 PM
Subject: Re: [GMCnet] How to heat up the Onan ignition?
Well, bollocks.
I get sparks visible in my spark plug tester from one wire (which read 1500
ohms) but not the other (which read as infinite resistance). Dangit, the
thing WAS working! I have proof!
So I have a bad wire? I mean, it certainly looks that way. Are these
"special" in some way plug wires?
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] How to heat up the Onan ignition? [message #194195 is a reply to message #194164] |
Fri, 28 December 2012 07:33 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Well, I'll go at this a different way. Static current through the coil does bupkis for spark. It is the >change< in flow through the primary which induces current in the secondary. Remember, this is a transformer, and transformers don't work on DC, only on changing current. Since we have DC, we change it using some sort of switch, either points or electronic.What happens is, when the points are closed, the coil magnetizes. Once it is fully magnetized (the primary forms an electromagnet, after all), the current through the points will increase, because there is now no counter EMF to buck the current. This matters really only when the ignition is on but the engine isn't running. Now consider what happens when it is time to fire the sparkplug(s). The points open, and current flow in the coil primary ceases. This causes the magnetic field about the coil to coll[pase. Picking the proper condenser value makes it collapse quite rapidly.
This change induces current flow in the secondary - or at least tries. Therefore the voltage across the secondary increases. It tries to go to infinity since it's looking at infinite resistance, but at some point the voltage produced is sufficient to cause the current to jump the plug() gap to ground. Spark. If there's bad insulation or a short someplace, the current takes this (least resistance) path to ground. Spark still, but not where it's wanted.
Note now, the value of all the components in this setup is pretty critical. When everything is correct, you get an intense magnetic field, and a hell of a SNAP across the plug gap(s).
Again, the Onan system works. I still recommend making it work before modifying it.
--johnny
'76 23' transmode norris
'76 palm beacgh
From: Ken Burton <n9cv@comcast.net>
To: gmclist@temp.gmcnet.org
Sent: Thursday, December 27, 2012 10:47 PM
Subject: Re: [GMCnet] How to heat up the Onan ignition?
Trying to get a higher voltage across a spark plug(s) using a points ignition is very difficult. The limiting factor is the points itself. The points are the switching device and can only carry a given amount of current. If the points are forced to move more than their designed load the points surface burns away while opening an closing.
The easiest way for me to explain it is to say that the coil is nothing more that a transformer with two sides. One side, in the case of the onan, is 12 volts and the other side is high voltage going to the spark plugs. You can not get more power out on the secondary side than you put in on the primary (12 volt) side. Power is volts multiplied by amps. Let use some simple numbers.
On the input lets say you have 12 volts and the points will carry 2.0 amps maximum. That means you have 2 amps X 12 volts or 24 watts input available for input. On the output side lets say you have 2400 volts jumping the plugs.
So on the output you have 2400 volts times ? amps which equals 24 watts. The question ? in this case would be .01 amps.
This means the example coil is wound at a 200 to 1 ratio. (12 volts in and 2400 volts out)
So if you want to increase the secondary voltage output you would have to wind a different coil that will take more current on the input side. Say 300 to 1 or 400 to 1.
The table looks like this
200 to 1 is 12 volts X 2 amps for 2400 volts out - 24 watts used
300 to 1 is 12 volts x 3 amps for 3600 volts out - 36 watts used
400 to 1 is 12 volts x 4 amps for 4800 volts out - 48 watts used
500 to 1 is 12 volts x 5 amps for 6000 volts out - 60 watts used
There is really more to it because the wattage and secondary amperage also goes up with the secondary voltage but for this explanation just go with the above numbers.
So to go to a higher spark plug voltage you need to replace the limiting factor with a something other than points. That is where transistorized switching comes in. Back in the early 70's that is what we did to increase performance with aftermarket products the the Delta Products unit. Later GM did the same thing with the HEI ignition. I also assume that the Pertronix unit would do the same thing but I do not know what it's current switching ability is. You would have to call them to see what their current switching spec is.
Keep in mind that the ONAN normally uses a lower ratio coil and no ignition resistor. Most automotive applications used a higher ratio coil with an ignition resistor. This allowed them to jumper out the resistor during starting and then revert to a lower input voltage while running to prevent points from burning.
Maybe someone else can explain it simply that I did.
Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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