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Onan: 1976 15 jc plug issue

luc102

Registered
Hi everyone .. hope all are well.
I got some iridium plugs....gap 28 for my jc to try to fix the famous small misfire at no load.. and it pretty much fixed it.. but..

When i removed the old new standard plugs i noticed the # 4 cylinder plug (gen end side) was a bit soothed while the other 3 were greyish white ( normal) so i took out my first set of plugs from the first tune up and one was also soothed a bit .

apart from the small no load misfire witch is now pretty much fixed it works just fine it can take no load to full load ( 64 amps on 240) .. timing is dead on.. new plug wires and electronic ignition converted.. note that the first set of plugs i had installed on the set it was running on new points and still i had a soothed one so i think its not a firing issue...??

it puffs a tiny bit at startup but does not take any oil and it puffed the same wen i bought it..valves are gapped to specs .. compression is within 2-5 psi on all 4 cylinders...
?? Valve issues .. ring issues..??on the # 4
Thanks
 

Wayne 440

Registered
Looks to me like the only issue is that you have run out of other things to worry about.:)

IF it was my set and it was not consuming oil, had compression close to specification (if it was low you would have said so, right?) "within 2-5 psi on all 4 cylinders... " and otherwise carried rated load with no issue, I would happily run it until some more serious evidence of a problem showed up. My guess is that a little oil is getting past a valve guide or the associated seal.
 

luc102

Registered
Well maybe i am looking for something.. been coopted up in house for 2 weeks now.. dam virus is getting closer ans closer..

Thanks.. ill keep an eye on it .. the #4 plug is just a bit off on color..

Major rain storm coming tonight lots of wind.. maybe ill at least get a power outage.. who knows.. get lucky ya know.. its so hard being an onan owner.. shish..
 

Leon N.

Registered
Like i said 2-5 psi between all 4 .. 152 to 156 psi
What is this guy talking about? Re “it puffs a tiny bit on startup”??? We need to know his complete model and serial number, what type of fuel is being used, was the machine designed for the type fuel being used?

It is not uncommon for some slight misfiring or popping at NL.If that is the problem he is talking about that usually is cured byopening the plug gap by a certain amount. If he is talking about an oil issue in one cylinder and his compression is OK, maybe he has a worn valve guide in one cylinder or too much oil is getting into the overhead valve chamber or he is using the wrong spark plug heat range.

WRT too much oil into the valve chamber, that could happen is someone messed around with the external oil line or the oil line restrictors that determine the correct amount of oil necessary to lubricate and cool the upper cylinder head valves,valve guides and cylinder head. We need more info the possibly help.
 

luc102

Registered
Hi Leon..no disrespect but..

First of all i am not .. this guy... second.. ive been here for quite a while now... luc102.. look it up and you'l have all you need on my 15 jc.. thanks.
A puff is a tiny puff of smoke upon startup..
my jc is so specked (thanks to this site) its probably better than when in came out of the plant.
it runs on 91 oct. gasoline ( no ethanol) on a brand new zenith carb , electric fuel pump.. 3 psi
Timing on mark.. plugs: brand new iridium BPR6HIX gap 28..
Ignition : pertronix
Valves ajusted per speck..
And no more misfire at no load...
It had a screwed up tri fuel carb when i bought it..
its probably just a leaky seat ... wont even bother opening it up since oil level is stable....
Thanks..
 

Attachments

Leon N.

Registered
Hi Leon..no disrespect but..

First of all i am not .. this guy... second.. ive been here for quite a while now... luc102.. look it up and you'l have all you need on my 15 jc.. thanks.
A puff is a tiny puff of smoke upon startup..
my jc is so specked (thanks to this site) its probably better than when in came out of the plant.
it runs on 91 oct. gasoline ( no ethanol) on a brand new zenith carb , electric fuel pump.. 3 psi
Timing on mark.. plugs: brand new iridium BPR6HIX gap 28..
Ignition : pertronix
Valves ajusted per speck..
And no more misfire at no load...
It had a screwed up tri fuel carb when i bought it..
its probably just a leaky seat ... wont even bother opening it up since oil level is stable....
Thanks..
Wow! I am impressed. I kind of thought that is what you meant by a “tiny puff”. Sounds like you like your JC and are taken good care of it. No offense intended but just a couple of thoughts you might want to ponder?

1) Your #4 cylinder probably has a leaky oil seal on one of the valves. That’s an relative easy fix.
2) Burning gasoline in a high compression JC designed to run on gaseous fuel?
 

luc102

Registered
Thank you Sir..no offence taken..
I very much value your input..

unfortunately i have no natural gas here and propane is twice the price of gasoline ..so i made a choice knowing the posible long term consequences.


that tiny puff was already there even at first start .. i exercise the set ounce every 2 weeks ( winter) and summer i go monthly .. if i run it weekly.. no puff at all so it is 99.9 % a valve seat or guide but very minor.. i could identify it and re-seat it but at this point i dont think its worth it but i will keep an eye on it

all i have on it is .. .. it was in a supermarket in a small town about 60 miles from me and it was on propane and the 2 bozos that bought it tried to convert it to gasoline but did not notice or know that the carb was missing all parts in the bowl and the main needle.. and told me it was running ... but running is a big word.. thus the reason for my buying a new carb from zenith.... thanks
 

Leon N.

Registered
Thank you Sir..no offence taken..
I very much value your input..

unfortunately i have no natural gas here and propane is twice the price of gasoline ..so i made a choice knowing the posible long term consequences.


that tiny puff was already there even at first start .. i exercise the set ounce every 2 weeks ( winter) and summer i go monthly .. if i run it weekly.. no puff at all so it is 99.9 % a valve seat or guide but very minor.. i could identify it and re-seat it but at this point i dont think its worth it but i will keep an eye on it

all i have on it is .. .. it was in a supermarket in a small town about 60 miles from me and it was on propane and the 2 bozos that bought it tried to convert it to gasoline but did not notice or know that the carb was missing all parts in the bowl and the main needle.. and told me it was running ... but running is a big word.. thus the reason for my buying a new carb from zenith.... thanks
Sounds like you are very proud of your JC plant and are aware of subtle but important details. I just want to point out a couple of things. I also note reference to Onan "Cummins".

The original Onan J-line plants were designed during the era of leaded gasoline. The gaseous plants were designed with more enduring internal parts as opposed to the gasoline-only plants. You mention using 91 octane gasoline, better known in the old days as high test gas. It is definitely needed in those early designed hi compression engines to prevent pre-ignition or knocking. I am sure you are aware of this and what problems pre-ignition knocking could cause in a electric plant running at full load for hours. The J-Line tri-fueled and gasoline-only plants were of low compression design where as the gaseous-only plants were of high compression design.

Funny story, as a side, when I drove my new 1962 Corvair Monza with a 9 t0 1 compression to Waco, Texas back in 1962. I had to use hi-test or what was also called white gas. Pulled into a gas station, told the attendant to fill er up and he warned me; "You want white gas? You will burnout your engine!" Obviously I told the attendant do not worry, just fill er up. Well I subsequently drove that air-cooled Corvair across the USA twice as I traveled between military assignments and never had a problem. Texas to CA across the desert and back to MA. Never got stuck in spite of what Ralph Nader claimed. Wish I had that car today. BTW, our former Stak associate, Ed Sparks had one under a tarp beside his house along with a Onan 10CW both of which I almost bit for. After Ed's funeral, Collete called asking me if I wanted them but I had to refuse.

Anyways, I trust this gentleman's high compression JC is running with 91 octane and with the proper ignition timing. This is one fine machine. About the only thing I would add would be surge protection on all the wired interfaces to protect that "electronic" voltage regulator.

Leon
 

Ray Lynch

Subscriber
Last Subscription Date
08/12/2019
Leon
I don't think all J line gaseous only plants are necessarily high compression. I have a gaseous only set that is not high compression. The high compression sets had the H177 option.
Ray
 

Leon N.

Registered
Leon
I don't think all J line gaseous only plants are necessarily high compression. I have a gaseous only set that is not high compression. The high compression sets had the H177 option.
Ray
Ray all I can say is what I know from looking at the early on J-Line PL for my JB built in 1966. That data indicates the hi-compression gaseous-only designs were introduced beginning factory spec S. That would connotate hi-compression, would it not? Beginning with factory build spec S Onan introduced a new PL for the piston assemblies which enabled the hi-compression gaseous-only design. Onan all ready had a separate part numbers for various parts depending if the application was gasoline-only as opposed to gas/gasoline, better known as tri-fueled.
I am not familiar with the term H177. Can you site an example where that shows up?
 

Ray Lynch

Subscriber
Last Subscription Date
08/12/2019
Ray all I can say is what I know from looking at the early on J-Line PL for my JB built in 1966. That data indicates the hi-compression gaseous-only designs were introduced beginning factory spec S. That would connotate hi-compression, would it not? Beginning with factory build spec S Onan introduced a new PL for the piston assemblies which enabled the hi-compression gaseous-only design. Onan all ready had a separate part numbers for various parts depending if the application was gasoline-only as opposed to gas/gasoline, better known as tri-fueled.
I am not familiar with the term H177. Can you site an example where that shows up?
Leon
See post #27 in attached link for options codes. See code H177.
I have a 705JB spec J built November 1965. It is a natural gas set. It is not high compression.
Your post #14 says the high compression gas sets were introduced beginning Spec S.
Again, not all JB/JC gas only sets are necessarily high compression.
Ray


https://www.smokstak.com/forum/threads/onan-option-codes.154358/page-2
 

Leon N.

Registered
Ray OK I stand corrected. Yes my tri-fueled JB built in 1966 is of low compression and the owners manual emphasizes a 20% hit when running on natural gas. My conclusions are drawn from the 1966 JB PLs as described in the Onan JB Owners Manual, 967-320. That is where my knowledge stops. My PLs do show the high compression design began with spec S as far as ordering the correct replacement parts at that time.
 
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