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04-20-2020, 05:28 PM | #1 |
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Onan QG 4000 RPM
I have a Onan QG 4000 generator in a class A MH that runs the same rpm with no load as it does at full load. Is this normal? I've had 4000's in the past and didn't remember them running at 3600 or so all the time. The generator has 236 hrs of usage. I pulled the air cleaner and checked to see if the throttle blade was intact and ok and it was.
Any help will be appreciated, thanks Jimmy Parker Last edited by jimmyparker; 04-20-2020 at 06:05 PM. Reason: additional info |
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04-20-2020, 08:54 PM | #2 |
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Re: Onan QG 4000 RPM
Engine rpm is read with a Frequency counting volt/ohm meter.
62 Hz no load 58 Hz full load And yes that is basically 3600 rpm all the time....each 1 Hz = 60 rpm of the engine The generator end/rotor is spinning at the same speed as the engine and the AC frequency indicates engine speed.. That’s ideal numbers and the governor controls that. Flyball type governor inside engine attached to the arm on top. Spring tension and arm leverage are adjustable. There is a low speed screw that may be interfering with governor arm action. It’s on the carb and you should be able to pull on the governor arm and lower the engine speed. If it does not come down some that screw needs to be backed up a little. That’s the usual scenario when engine speed does not move much. It usually causes them to overspeed once load is removed or at least it can cause that occasionally. There really very simple but complicated ! Lol
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Rich Biebel S/C 1479 Last edited by Rich Biebel; 04-21-2020 at 06:49 AM. |
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04-21-2020, 11:20 AM | #3 |
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Re: Onan QG 4000 RPM
Thanks Rich, I'm sure you have saved Class Racer members thousands of dollars with your expert advice.
I checked that governor throttle arm and it was not returning all the way to the set screw, I took a slight amount of tension off the governor spring and it now returns to the stop and does affect the running speed. I surprised that Onan still offers these generators and even more surprised the RV builders still install them. Thanks again, Jimmy Parker |
04-21-2020, 12:07 PM | #4 |
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Re: Onan QG 4000 RPM
They are my favorite model and I own 2 myself....
Most Every Class C Motorhome has one..... I have one in my trailer and one in my Class C Motorhome.... They are not like the older 1800 rpm units for sure and are far less durable. Older models were twin cylinder flathead engines that ran 1800 From a 4 to a 7 KW 20 years ago they started making their modern versions.... Single cylinder 3600 rpm....on the QG 4000's......The 5.5 and 7kw's are twin cylinder and nothing like the 4's.... Onan stopped making their own engines back then and everything they build uses an import built engine......No big surprise.... For those that don't know..... A modern Onan QG 4000 has NO low oil shutdown.... If it runs low on oil it will at the very least seize up and usually much worse..... The aluminum rod usually blows up and takes out the engine. They only hold about 1-1/2 quarts of oil and it should be changed often.....and checked often.....No filter.....splash oil.... I saw more than one that blew up and really busted up everything in there.....changing an engine is not a good option so it winds up being trashed....
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04-22-2020, 12:57 PM | #5 | |
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Re: Onan QG 4000 RPM
Quote:
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04-22-2020, 01:13 PM | #6 |
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Re: Onan QG 4000 RPM
Interested in Rich's recommendation as well. The oil fill tag attached by the Onan technician indicated a different oil than is recommended by their manual. My previous Onan was a larger model with filter and at the initial 50 hour change the oil looked better than this one did at 20 hours. Going to make sure I don't go past 30 hours without a change from now on.
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06-11-2020, 11:28 PM | #7 | |
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Re: Onan QG 4000 RPM
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06-12-2020, 11:01 AM | #8 |
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Re: Onan QG 4000 RPM
I have noticed more racers are going to the inverter style generators like the Honda EU7000iS and the Honda EU3000iS.
They are very quiet and only run as many RPM as they need to cover the load. However they appear to need to have the generator door opened and pulled out on a slide to get proper cooling. Connecting an exhaust pipe on the EU3000iS may take a special kit. Of course these generators are pretty expensive but other inverter generator are starting to show up on the market. However the Onans are not inexpensive either. |
06-13-2020, 01:05 PM | #9 |
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Re: Onan QG 4000 RPM
4000 is barely enough for a trailer. I put a 6.5 in mine and it runs everything very easily. I bought an old Onan 6.5 with low hours for $500. It’s one of the 1800 rpm twin cylinder units. They are very quiet and reliable. Just search on Craig’s list or Facebook marketplace. There are usually some for sale there.
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