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Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L


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  #31  
Old 02-08-2018, 10:14:38 PM
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Default Re: Onan JC - Problem with My “Very Reliable” 15JC-3R/3998L

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Originally Posted by maineboy View Post
I checked compression and it showed 80-90psi on all 4 cylinders.
Seems a little low, I think you should be closer to 120. Check the book.
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  #32  
Old 02-08-2018, 10:52:45 PM
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

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Originally Posted by KPack View Post
Did you use a coil with a resistor or without.
Without resistor - Onan Green label part 0166-0863 it has text printed on the coil that say use without external resistor.
I was told it was fine? Should I use one with a resistor?

Quote:
Originally Posted by Max Thompson View Post
Seems a little low, I think you should be closer to 120. Check the book.
First revolution 90; second rev 100; 3rd 120 psi.
When doing a compression test I thought you were supposed to use the first compression stroke. Yes / no?
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  #33  
Old 02-08-2018, 11:06:57 PM
Leon N. Leon N. is offline
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

Can not tell without the factory build spec, but I suspect your JC is of the same vintage as my JB and you mentioned it was "converted " to LP and that may be a hint that is is of a low compression design. My JB measured 80 -90 psi. I suspect your machine was built in the early 60's.

You mentioned a "weak spark" ? How did you determine that? I suspect there is another capacitor in the coil primary circuit. Did you ohm it out to make sure it was good? Did you check the distributor rotor and cap for cleanliness inside and outside? Could be some high voltage is leaking off to ground.
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  #34  
Old 02-08-2018, 11:38:16 PM
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

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Originally Posted by Leon N. View Post
Can not tell without the factory build spec, but I suspect your JC is of the same vintage as my JB and you mentioned it was "converted " to LP and that may be a hint that is is of a low compression design. My JB measured 80 -90 psi. I suspect your machine was built in the early 60's.

You mentioned a "weak spark" ? How did you determine that? I suspect there is another capacitor in the coil primary circuit. Did you ohm it out to make sure it was good? Did you check the distributor rotor and cap for cleanliness inside and outside? Could be some high voltage is leaking off to ground.
I was just looking at the visual spark, it was not as blue as I’m used to seeing on other machines (not very scientific). The points, distributor cap, rotor button and resistor are brand new. You mentioned some voltage leaking to ground, I’m going to check the ground wire from the coil to the distributor and point contact post. I will check resistance on the capacitor.
Thank you for the help.
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  #35  
Old 02-09-2018, 02:58:15 AM
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

Probably just replace the capacitor it’s cheap enough. 120 is good compression after a few rotations , basicly it stops building and that is your number. Cheers Dan
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  #36  
Old 02-11-2018, 06:52:46 PM
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Default UPDATE: she's running again Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

I tried and I failed, I tried and I failed, I tried and I WON!
I just wanted to say thanks to everyone for their help on my JC.
In the end it was timing! Which many of you had pointed out, but sometimes I’m a bit slow.
After changing my KN regulator and making sure it had 11” W.C. I then tried a new coil, condensers, distributor cap, rotor button, points, plugs, etc, etc.. I checked the compression and chased down every ground, centrifugal cut-off, low oil pressure switch, LP gas solenoid…
I knew I had spark, gas and compression, but was the spark being delivered at the right time? NO... the distributor had slipped.
I think it happened when I exercised my JC at -25 F. I think the metal had shrunk in the cold and the distributor vibrated to a very advanced or retarded position whereby she died and would not light. In desperation (no timing light) I found TC and looked at the position of the rotor button and was horrified, not even close. Well a little twist to the left, nothing- then a twist to the right and she lit right up and now she’s purring like kitten again.
A special Thanks to Billy J and Leon for their words of wisdom and more importantly - Thank you for your service to our nation.
All the best,
Jason
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  #37  
Old 02-11-2018, 07:04:41 PM
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

So have you now checked the timing with a timing light or by the static method? You want to make sure you are timed to specifications because you can cause engine damage if it is not set properly. Too retarded, the engine can over heat and have poor performance. Too advanced can cause internal combustion chamber temperatures to run to hot and if you are running heavy loads, can actually cause a piston to burn. Just FYI
Glad you found the issue.
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  #38  
Old 02-11-2018, 08:54:42 PM
Leon N. Leon N. is offline
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

Wow! Glad you found the problem. Who was the last person that installed your distributor? That distributor clamp bolt should have never never come loose, even at 25 below. I remeber working on old cars that employed the same design.

I hope you are using a very low viscosity synthetic oil at those temps.

BTW Have you ever had to remove your Magneciter end cover and hit the red button to flash the field so that voltage would build up? If you use the machine regularly, you probably have no need to push the red button.
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  #39  
Old 02-12-2018, 10:04:30 AM
maineboy maineboy is offline
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

[QUOTE=Leon N.;1460985]Wow! Glad you found the problem. Who was the last person that installed your distributor?
BTW Have you ever had to remove your Magneciter end cover and hit the red button to flash the field so that voltage would build up?

Well, the last person to touch the distributor clamp was probably me, but it was a long time ago, so I could easily blame it on my dog.
I’ve never had to “flash” the gen, to be honest - I’m not even sure what that means, I’ll go do some reading.
The JC 15KW normally makes great power, it allows me to run my home at pretty much full capacity.
I’m going to set the timing at 35 BTC and then adjust the gov so that it makes 60hrz through the power range of load. Does that sound like a good plan?
Thanks again for all of the help
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  #40  
Old 02-12-2018, 02:22:20 PM
Leon N. Leon N. is offline
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Default Re: Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

Yes you have a good plan! Looking at your JC model overhaul manual, 967-500, you are correct to set the timing advanced, plant running on LP gas at 35 degrees BTC. If you set the timing, plant stopped, set it at 10 degrees BTC with the caveat [ 20 degrees BTC for units with shielded distributor]. I do not know if that caveat applies to your machine? Perhaps you can enlighten us.

I recall working on old style distributors which employed a spring type clamp for the distributor lock down, that seemed to prevent what might have happened in your situation@ 25 below.

Your JC like mine employs what is called droop style governor. It is spec'd to hold the frequency, i.e., RPM, within 5%. And the plant is rated to provide rated output power@60Hz. Therefore, most folks set the NL RPM/frequency at just over 60Hz to compensate for the 3 Hz (5%) droop. In my experience, I set the NL frequency at 60.5-61 Hz because most of the time the loads are well below the generators rated output. Obviously, my clocks run a tad fast and when fully loaded, the frequency is tad below 60 but so what since the appliances do not seem to mind.

Just never let your machine operate much below normal operating range or you will over heat the magneciters exciter toroid coils and let out the so called magic smoke.

Also, if I recall, your JC was built to factory spec "L". That means it has an early version of the magneciter which does not employ automatic field flashing on startup. Field flashing in this case is temporarily applying a DC voltage to the revolving field, i.e., the rotor, to replace lost residual magnetism necessary to get voltage induced in the stator windings which subsequently power the exciter which regulates the magnecitors output voltage to within the specified range of 3%.

Also, your magneciter has a temporarily over load rating of close to 20% with a transient response suitable for motor starting of 3 times rated output.

Bottom Line: You have a gem here, take good care of it and it will outlast you. Mine is coming up of 50 years of service very soon.
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