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Old 09-07-2019, 12:35 AM   #1
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Default Help with Onan 2.8 Generator

Generator was running fine, then would only run while switch was held down, but was not generating any 110 volt power. A visit to Cummins Service Center resulted in a diagnosis of an open in the rotor. (control board and voltage regulator were fine) After having rotor rewound and reassembling the generator, everything work although it was running a little rough, surging and hunting. While trying to fix this, when I tried to start it , I heard a pop and it has not fired since. It cranks, has plenty of gas, has compression, and spark, but will not fire. Spraying starter fluid in carburetor makes no difference, no fire. Tried cleaning carburetor , no help. Purchase an after market carburetor, no difference. What next, timing issue?? How do you check timing.?? Do I give up and look for a running used 2.8, the only thing that will fit in Roadtrek. Any suggestions will be greatly appreciated. Thanks for your help!
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Old 09-07-2019, 02:23 AM   #2
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I have some issues with my generator and your experience is why I dread having it worked on. Hourly rates are very expensive and I fear finding someone who is competent and will do the job right. Sounds like they didn't take the time to properly adjust the governor which might account for your initial surging problem.

I'd call the person who worked on it and ask if they are willing to diagnose your current problem for free since they just worked on it. It may not be related, and they should not be asked to do extra work for free, just diagnose it. Could be an easy fix based on all you've done. If not, it could be the nightmare I describe above (spend a bunch of money & time, only to not get it running good).
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Old 09-07-2019, 01:38 PM   #3
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If you have spark, fuel and compression, I think I would be looking at the ignition timing. If it slipped that would give the pop and also the no start. I am not familiar with the design so can't help on how ot check or adjust.
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Old 09-07-2019, 05:25 PM   #4
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The Onan 2.8 ignition system is a magneto/coil pack system consisting of only 2 components. The Flywheel has a magnet on it which passes a coil generating a pulse which feeds the coil pack. There is no timing adjustment, it is mechanically fixed. The coil pack consists of a capacitor which charges up and discharges through the coil generating the high voltage for the spark. The coil pack is a potted package and not repairable. It is the most likely point of failure. The pick up coil could have shorted out and, I believe that this too, is replaceable. Of course, the spark plug could have some kind of fault. That's about all there is to the ignition system. If you tried starting fluid and got no response this pretty much eliminates the fuel system (pump, carburetor and filter.).
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Old 09-07-2019, 06:25 PM   #5
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There is no timing adjustment, it is mechanically fixed.
Amazing!
No wonder they all run like crap.
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Old 09-07-2019, 06:54 PM   #6
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Amazing!
No wonder they all run like crap.

On many of that kind of system, the timing can get off if the flywheel key is broken or bent, and in some cases the timing is set by using offset keys, which if put in backwards can really mess things up. If they have a timing spec available, you might be able to get it to crank fast enough to see what the timing is at with a timing light or multimeter.



Why is it that we see so very many Onans that come out of the service centers worse off than they went in? Crazy.
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Old 09-07-2019, 07:21 PM   #7
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Quote:
Originally Posted by JohnnyFry View Post
The Onan 2.8 ignition system is a magneto/coil pack system consisting of only 2 components. The Flywheel has a magnet on it which passes a coil generating a pulse which feeds the coil pack. There is no timing adjustment, it is mechanically fixed. The coil pack consists of a capacitor which charges up and discharges through the coil generating the high voltage for the spark. The coil pack is a potted package and not repairable. It is the most likely point of failure. The pick up coil could have shorted out and, I believe that this too, is replaceable. Of course, the spark plug could have some kind of fault. That's about all there is to the ignition system. If you tried starting fluid and got no response this pretty much eliminates the fuel system (pump, carburetor and filter.).
Pretty much like the small engines I repaired 45 years ago - without points and condenser.

How about the plug wire? Either open or short to ground? Corroded or saturated with oil?

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On many of that kind of system, the timing can get off if the flywheel key is broken or bent,
Yep - I've seen that on small engines a few times.
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Old 09-07-2019, 08:35 PM   #8
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Why is it that we see so very many Onans that come out of the service centers worse off than they went in? Crazy.
This discussion is supportive of my theory that one might be better off taking these things to your neighborhood lawn mower guy rather than to Onan.
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Old 09-07-2019, 09:32 PM   #9
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The plug wire appears to be potted into the module. It is only a few inches long.
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Old 09-12-2019, 05:51 PM   #10
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Sounds like a problem that I had with mine. Turned out to be the intake valve pushrod had got itself out from under the rocker arm. It appeared to have compression but the intake valve never opened. The valve rocker arm cover is the part that has the information label on it. If you remove the cover you will probably have to make or buy a new gasket for it. No big deal.
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Old 09-12-2019, 09:40 PM   #11
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Took my 2800 to Cummings dealer twice in my area. Never ran right and just started other problems. Took to repair shop and although just as expensive. Got it running right. It is unfortunately hit or miss. I think I have replace nearly every part once or twice now. Really wish Honda made one to fit in compartment.
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Old 09-12-2019, 10:43 PM   #12
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Took my 2800 to Cummings dealer twice in my area. Never ran right and just started other problems. Took to repair shop and although just as expensive. Got it running right. It is unfortunately hit or miss. I think I have replace nearly every part once or twice now. Really wish Honda made one to fit in compartment.

Another data point that is reinforcing Avanti's idea that a non-Onan shop would probably have a higher probability of success than an Onan Service Center.


There really is no excuse for a factory trained workforce in a company business, can't seem to fix their own products decently.
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Old 09-13-2019, 05:38 PM   #13
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I had similar problem. It was a broken starter.
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