Onan 6.5 KW sounds horrible to me.

Started by 1990HR, May 13, 2015, 01:07 AM

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Bear with me a second.
My generator would idle rough and just die put under a load.
I checked the spark plugs and were a little fouled, replaced them.
Changed the oil, checked compression and was fine at 115 PSI on both cylinders.
Removed carb and cleaned it. The jets were fine but got a little debris out of the needle and seat inlet.
Installed carb and installed an inline fuel filter.
After the float bowl filled up, the generator runs fine. Turned on the AC and it never even changed speed, like it didn't care.

Here is my problem. It sounds like crap.
I'm not an Onan generator mechanic so I don't know what they are supposed to sound like.
It sounds like an old tractor.
I'm a motorcycle mechanic of 22 years now and I know if a bike came in sounding like this I would be tearing it down.
I know air cooled engines make a lot more noise than water cooled engines but I work on a lot of air cooled Harley Davidson and other makes.

Here is what the generator sounds like:
Not my generator but found the video and it sounds similar.

I have not taken a stethoscope to it to find the source of the noise or anything, wanted to know if these generators are just loose running, noise making engine?

Thanks guys for your time.


Recorded sound is not like live but that one sounds like it could use a valve clearance adjustment. The hunting/surging could be a lean mixture or a governor issue, sometimes just a simple lube of the linkage.
Don and Mary
2000 TC1000 Bluebird bus conv.


We have tons of generator manuals here.  Find your model number, chances are we have it.  Using the troubleshooting guides are a valuable method to fix the problem, or at least narrow it down and get it solved with help from our CWVRV members.
1969 D22, 2 x 1974 D24 Indians, 1977 27' Itasca


It does not sound like excessive valve lash, wrong timing of sound.
Sounds more like piston slap or bad crank bearings. But, if they are loose engines you will hear piston slap and that would be normal for that engine.

I do have the manuals for the generator and the generator runs just fine but seems noisy to me is all.
I'll see if it starts getting louder or making other sounds before I tear it down.


Them old onans are noisy like that, but if it surges like that something is wrong. Most likely a carb adjustment, or points and condenser. Them old onans are hard on points as far as I'm concerned. I used to go through a set almost every year when I had a bfa 4000. Point gap is critical on them too. Might also check the fuel requirements for that set to make sure unleaded is ok to run.


Blubird5750, it's a 1990 so it does have hardened valve seats for unleaded fuel, also it's not surging like the one in the video.
I just used that video because it sounded similar to mine.
I actually like the old ignition point system sometimes because they are easy.
Had an old 1960's dirt bike once come in with no spark. Had a bad capacitor that was no longer available.
Ran down to Radio Shack and they had one with the correct farad rating and fixed the old bike.
Customer was pretty happy.


Older Onans run at 1800 rpm unlike many modern ones that run at 3600 rpm.  Being a 2 cylinder engine, at 1800 they do sound like a tractor.



mine sounds like it's going to jump right out of the generator bay.


Quote from: DaveVA78Chieftain on May 14, 2015, 07:53 PM
Older Onans run at 1800 rpm unlike many modern ones that run at 3600 rpm.  Being a 2 cylinder engine, at 1800 they do sound like a tractor.


So basically they went from 4 poles to 2 poles then.
I guess I could just put Dynamat on the compartment walls to isolate the noise.