Home » Public Forums » GMCnet » ONAN Generator (Not firing)
| ONAN Generator [message #357712] |
Fri, 14 August 2020 18:35  |
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Samuel Ferguson
Messages: 107
Registered: September 2019
Location: Pittsfield, Illinois
Karma: 0
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Rebuilt carb and put a new fuel line on. Put a set points and condenser in.
Right spark plug does not appear to be getting any spark. Left plug is getting hot to the touch, while right plug is not.
Engine ran fine until I noticed old fuel line and bowl gasket leaking and did the mentioned work to it.
Samuel Ferguson
Summer Hill, Illinois
(West Central Illinois)
1976 GMC Palm Beach
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| Re: [GMCnet] ONAN Generator [message #357713 is a reply to message #357712] |
Fri, 14 August 2020 18:59  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Steve,
The Onan's ignition system is known as a "lost spark" system. That means
that BOTH plugs fire at the same time -- always. They can't do otherwise
because they're connected to each end of a single secondary winding in the
ignition coil. The principle is that one of the pistons will be on the
compression stroke while the other is on the exhaust stroke. That is,
there will be ignition at the end-of-compression/beginning-of-power, but
not at the end-of-exhaust/beginning-of-intake phases.
So, what you need to do first is determine why the cold plug is cold. Pull
that plug, re-connect its plug wire, and ground it to the block. When you
hit the starter, there should be arcing between the plug's points. If
there's not, that plug wire is being shorted to the block somewhere between
the plug and the coil (or, very unlikely, the coils' suddenly shorted
internally). You'll have to find and correct that short to let the voltage
that IS reaching the other plug reach the cold one also.
If there is spark at the plug (as I expect), then you obviously have
another problem -- possibly fuel delivery to that cylinder. At least
you've eliminated the ignition system as a problem.
HTH,
Ken H.
On Fri, Aug 14, 2020 at 7:36 PM Samuel Ferguson via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Rebuilt carb and put a new fuel line on. Put a set points and condenser in.
> Right spark plug does not appear to be getting any spark. Left plug is
> getting hot to the touch, while right plug is not.
> Engine ran fine until I noticed old fuel line and bowl gasket leaking and
> did the mentioned work to it.
> --
> Samuel Ferguson
> Pittsfield, Illinois
> (West Central Illinois)
> 1976 GMC Palm Beach
>
> _______________________________________________
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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: ONAN Generator [message #357717 is a reply to message #357712] |
Fri, 14 August 2020 19:47 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Another way to think of it is the plugs are in series with the block serving to connect the two. If you disconnect one you get nothing. And yes the electricity flows from center to side on one and side to center on the other.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] ONAN Generator [message #357721 is a reply to message #357714] |
Sat, 15 August 2020 01:12 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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As Colonel Ken stated, in a "wasted spark" system it is almost impossible to fire one plug without the other one firing too because the two are in series. One exception would be if one plug wire was shorted to ground or if the non firing plug is internally shorted. We see the second scenario frequently on low compression airplane engines due to lead build up from using 100 octane fuel in 80-87 octane engines. Cleaning the plug(s) and picking the lead out with a small pick fixes the problem.
You will not see lead in car engines because they have not sold leaded auto gas in many years. An excess of carbon and an oil or soot can foul a plug and cause the same problem as lead. So clean and recheck the gap on the plug that is not firing. Also verify that the plug wire is not routed is such a way that is could short to ground.
Also so do not check one plug for spark with the other one removed, or the other spark wire not connected to the coil and plug.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] ONAN Generator [message #357739 is a reply to message #357721] |
Sun, 16 August 2020 10:22 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Ken,
I believe that this is a parallel system as the current goes thru each plug and then to ground and not one plug and then the other plug and ground. I remember working on series, parallel and series parallel diagrams for my one electronics class, if wrong I need to know why.
JR
> On Aug 15, 2020, at 2:12 AM, Ken Burton via Gmclist wrote:
>
> As Colonel Ken stated, in a "wasted spark" system it is almost impossible to fire one plug without the other one firing too because the two are in
> series. One exception would be if one plug wire was shorted to ground or if the non firing plug is internally shorted. We see the second scenario
> frequently on low compression airplane engines due to lead build up from using 100 octane fuel in 80-87 octane engines. Cleaning the plug(s) and
> picking the lead out with a small pick fixes the problem.
>
> You will not see lead in car engines because they have not sold leaded auto gas in many years. An excess of carbon and an oil or soot can foul a plug
> and cause the same problem as lead. So clean and recheck the gap on the plug that is not firing. Also verify that the plug wire is not routed is
> such a way that is could short to ground.
>
> Also so do not check one plug for spark with the other one removed, or the other spark wire not connected to the coil and plug.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] ONAN Generator [message #357741 is a reply to message #357739] |
Sun, 16 August 2020 10:52 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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If you look at the ONAN coil, it is technically a step up transformer. One
large diameter sized wire that carries the primary current from B+ to
ground. As the current passes through the windings it creates a very strong
magnetic field, the lines of which also cut through the thousands of turns
of the secondary coil windings, "INDUCING" a high voltage/low amperage
electron flow in the secondary windings. The ignition points/condenser team
up to turn the primary current on and off when the points open and close.
This collapsing magnetic field produces a very high voltage/short duration
current flow that goes to ground through the plug wires and plugs, arcing
across the plug electrodes on their way to ground. This arcing ignites the
air/fuel mixture in the cylinder if it is present. If no fuel/air mix is
present, then that spark is "wasted". That is why the ONAN ignition system
is called a "waste spark" ignition system. Clear as mud, right?
Jim Hupy
Salem, Oregon
On Sun, Aug 16, 2020, 8:23 AM John Wright via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Ken,
> I believe that this is a parallel system as the current goes thru each
> plug and then to ground and not one plug and then the other plug and
> ground. I remember working on series, parallel and series parallel
> diagrams for my one electronics class, if wrong I need to know why.
>
> JR
>> On Aug 15, 2020, at 2:12 AM, Ken Burton via Gmclist gmclist@list.gmcnet.org> wrote:
>>
>> As Colonel Ken stated, in a "wasted spark" system it is almost
> impossible to fire one plug without the other one firing too because the
> two are in
>> series. One exception would be if one plug wire was shorted to ground
> or if the non firing plug is internally shorted. We see the second scenario
>> frequently on low compression airplane engines due to lead build up from
> using 100 octane fuel in 80-87 octane engines. Cleaning the plug(s) and
>> picking the lead out with a small pick fixes the problem.
>>
>> You will not see lead in car engines because they have not sold leaded
> auto gas in many years. An excess of carbon and an oil or soot can foul a
> plug
>> and cause the same problem as lead. So clean and recheck the gap on the
> plug that is not firing. Also verify that the plug wire is not routed is
>> such a way that is could short to ground.
>>
>> Also so do not check one plug for spark with the other one removed, or
> the other spark wire not connected to the coil and plug.
>> --
>> Ken Burton - N9KB
>> 76 Palm Beach
>> Hebron, Indiana
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
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| Re: [GMCnet] ONAN Generator [message #357742 is a reply to message #357739] |
Sun, 16 August 2020 11:11 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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powwerjon wrote on Sun, 16 August 2020 11:22Ken,
I believe that this is a parallel system as the current goes thru each plug and then to ground and not one plug and then the other plug and ground. I remember working on series, parallel and series parallel diagrams for my one electronics class, if wrong I need to know why.
JR
JR,
I think you misunderstood what KenB was saying.
Spark plugs cannot be in parallel as typically defined because only one plug will fire. They cannot be in series as usually defined because the base of the plug would have to be insulated at plug firing potential and this would be difficult. There are some gas turbines that do this for the igniters, but you don't want to know what those cost.
The Onan like so many other engines with a double ended coil have a secondary winding that has no grounded end. There is a spark plug at each end, so spark goes both ways. Ego, if one plug fires the other must unless there is some failure in the components. This setup has even been used on some passcar motors as well as little engines.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] ONAN Generator [message #357744 is a reply to message #357742] |
Sun, 16 August 2020 11:20 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Senior Member |
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Thanks for the info.
JR
> On Aug 16, 2020, at 12:11 PM, Matt Colie via Gmclist wrote:
>
> powwerjon wrote on Sun, 16 August 2020 11:22
>> Ken,
>> I believe that this is a parallel system as the current goes thru each plug and then to ground and not one plug and then the other plug and
>> ground. I remember working on series, parallel and series parallel diagrams for my one electronics class, if wrong I need to know why.
>>
>> JR
>
> JR,
>
> I think you misunderstood what KenB was saying.
>
> Spark plugs cannot be in parallel as typically defined because only one plug will fire. They cannot be in series as usually defined because the base
> of the plug would have to be insulated at plug firing potential and this would be difficult. There are some gas turbines that do this for the
> igniters, but you don't want to know what those cost.
>
> The Onan like so many other engines with a double ended coil have a secondary winding that has no grounded end. There is a spark plug at each end, so
> spark goes both ways. Ego, if one plug fires the other must unless there is some failure in the components. This setup has even been used on some
> passcar motors as well as little engines.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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