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Onan motor spitting oil


Greetings:wave: One of my Onan welder generators is spitting oil. It's a twin cylinder on a Miller...

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Old 07-03-2013, 08:53 PM
Popgunner Popgunner is offline
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Default Onan motor spitting oil

Greetings

One of my Onan welder generators is spitting oil.
It's a twin cylinder on a Miller "Blue Charger" 1981 vintage.
This unit welds, 120v & 24v power, gas.
Has sat for two years unused & covered. Went to start it up & it runs fine for about a minute & then starts spitting oil out the exhausts. No blue smoke when it's cold & just started, no smoke while it's spitting, just quite a bit of oil spitting.
I'm afraid moisture may have caused the rings to seize & as the cylinders heat up & expand there's no oil control. Just guessing.
Any help on a fix would be appreciated.
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Old 07-03-2013, 09:25 PM
Kpack Kpack is offline
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Default Re: Onan motor spitting oil

The other guys will be along but read up on wet staking.
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Old 07-03-2013, 09:41 PM
David C David C is offline
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Default Re: Onan motor spitting oil

Make sure the engine is running on both cylinders. Check the temperature of the heads or exhaust pipe to see if they warm up at the same rate.

David C.
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Old 07-03-2013, 09:48 PM
Kpack Kpack is offline
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Default Re: Onan motor spitting oil

Excuse me I thought it was a diesel didn't see it was gas.
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Old 07-03-2013, 10:07 PM
len k len k is offline
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Default Re: Onan motor spitting oil

In general almost all gas engines have oil breather hose going to carb intake, so engine burns crankcase vapors. Check that that line is not supplying "tons" of liquid oil to carb,

Better yet just disconnect it and see if problem stops.
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Old 07-03-2013, 11:55 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Onan motor spitting oil

Wow. I hope someone that understands this can jump in here. I'm at a loss to explain how an engine can be passing oil out the exhaust and not be smoking...

Now, OTOH, I have an old CCK engine that blows oil out the breather - that I understand.....

Last edited by Jim McIntyre; 07-04-2013 at 10:05 AM.
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Old 07-04-2013, 02:27 AM
Popgunner Popgunner is offline
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Default Re: Onan motor spitting oil

I'll check/disconnect any hoses & see what happens.
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Old 07-04-2013, 06:44 AM
David C David C is offline
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Default Re: Onan motor spitting oil

Quote:
I'm at a loss to explain how an engine can be passing out the exhaust and not be smoking...
Jim,
Since one cylinder probably had at least one valve open, while setting, that cylinder may have stuck rings from condensation & corrosion. If that cylinder is not firing and the rings are stuck, it can pump oil out of that cylinder. If the engine is not loaded to heat the exhaust up, the oil might be able to get through the exhaust without burning.

If the engine does have stuck rings, it should have a considerable amount of blowby coming out of the crankcase breather.

David C.

David C.
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Old 07-04-2013, 08:42 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan motor spitting oil

I am working on a CCK. Running on one cylinder other cylinder spitting oil. Found stuck exhuast valve.
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Old 07-05-2013, 03:36 PM
Popgunner Popgunner is offline
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Default Re: Onan motor spitting oil

I may have misled with "engine doesnt smoke cold & doesnt smoke while spitting" statement.
It doesn't smoke cold when started & for the first minute warming up but then oil spits hard out the mufflers(that point straight up) & showers me with oil so I cut the ignition switch about the same time the plugs foul out with oil. I'm sure if the amount of oil were less it would smoke like the devil. So much oil it just puts the fire out so to speak.
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Old 07-05-2013, 04:09 PM
len k len k is offline
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Default Re: Onan motor spitting oil

Till you said plug was oiled, I wondered if kids poured oil into muffler to "protect" it.
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Old 07-05-2013, 07:24 PM
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Default Re: Onan motor spitting oil

I checked & it has a breather tube from the crank case that goes up to the air cleaner housing but the air cleaner/housing doesn't show oil & disconnected doesn't make a difference. seems to have steel wool packed into the breather tube as it exits the case. Wonder if it could be blocked from there down?
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Old 07-05-2013, 07:59 PM
len k len k is offline
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Default Re: Onan motor spitting oil

Sounds like the oil breather is not the source of the oil (thur carb).
Oiled plug...Need a path from oil source to combustion chamber. On cars he usual suspects are piston rings and valve guides (and their O-rings). Intake valve in this case as oil is in combustion chamber. If you saw it run well several years ago I would guess it's not a cracked block. But others here know the quirks of Onans better than me.

There is something you can pour down the carb while engine is running to free up the rings. Marval Mystery oil maybe or gumout??? I forget.
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Old 07-05-2013, 08:09 PM
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Default Re: Onan motor spitting oil

Is the oil at the proper level? Could the fuel pump be leaking, filling the crankcase with gasoline?

David C.
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Old 07-05-2013, 08:41 PM
len k len k is offline
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Default Re: Onan motor spitting oil

Talked with dad (car engine expert). To free up rings, add some Marval Mystery oil in crankcase and run it, may take a few days. Also can pour down carb a little at a time, on cars he dumps alot in at end ~spray paint cap full and shuts off engine. But I don't think I would dump alot in at end in this case, it's a small displacement engine, too easy to add too much. Oil is not compressable, don't want to crack piston or a rod.

If that doesn't work get engine hot, dripple gumout down carb, then shut it off for overnight. Don't add it too fast or you'll wash oil off cylinder walls and can score them.

Porportions.... Using a plastic cap from a spray paint can ....at the end he dumped 1/2 capfull in. It was a large V-8.... 350 (5.7Liter = 5700CC) . Your engine is ~ <1000 CC so ratio acordingly if you try it and err on the low side to avoid hydrolock damage.
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Old 07-06-2013, 07:05 PM
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Default Re: Onan motor spitting oil

Wel David I did check for gas & water in oil and oil level. Changed oil too & it's non-contaminated & at correct level. I will try the Marvel oil & let it soak.
Thanks all for your pointers
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Old 07-07-2013, 12:04 AM
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Default Re: Onan motor spitting oil

Just thought of something today. Marval Mystery oil sounds ok. But gumout is basically a solvent, it can wash the lubricating motor oil off cylinder walls. On the cars we used it on the blocks were cast iron and pistons aluminum. I don't know your Onan but it likely has aluminum for both block and pistons. That means a higher chance of gallling. You may want to test gumout on a old junkable cheap lawnmower engine first.

Typically to prevent galling when designing sliding fits you make one part with a harder metal than the other. Galling can become an issue when both parts are ~ same hardness. Think Chevy Vega engine , aluminum block.
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Old 07-07-2013, 12:33 AM
lokay5 lokay5 is offline
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Default Re: Onan motor spitting oil

"Typically to prevent galling when designing sliding fits you make one part with a harder metal than the other. Galling can become an issue when both parts are ~ same hardness. Think Chevy Vega engine , aluminum block."

Onan, Vega, Cool Bore Briggs & Stratton, West Bend & Clinton 2 & 4 cycle, think aluminum block, cast iron piston rings....
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Old 07-07-2013, 12:54 AM
len k len k is offline
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Default Re: Onan motor spitting oil

But during stoke I think in addition to ring, the angles of rod forces should make piston also contact cylinder. But I haven't looked at locations of rings along piston. I "assume" they are grouped near the top. I do remember the piston skirts were long and no rings in ~50/60's cars dad did ring jobs on.

I did think about Onans and Vegas, and wondered why onans have long life and Vegas didn't. I know vega blocks used a special Aluminum alloy with hard spheres of metal or carbide?? dispursed in the matrix. But that doesn't support my theory.

---------- Post added at 12:54 AM ---------- Previous post was at 12:49 AM ----------

Vegas needed a special machining/honing method so aluminum was undercut and the harder "microspheres" where left on surface for piston to run on.
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Old 07-07-2013, 08:22 AM
David C David C is offline
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Default Re: Onan motor spitting oil

I don't think that Onan built an aluminum engine that did not have cast iron sleeves. The NH and BF models have cast iron sleeves, so I don't think you have to worry about galling.

Is there a chance that the engine is running so rich from a carb or choke problem that the slobber is actually more of a gasoline/carbon mixture than oil?

I have a 4.0BF Onan that has stuck rings from water damage. I had to pull the heads and scrape rust from the bore to free it up. I have to remove the crankcase breather to get it to run correctly due to the massive amount of blow-by. It has more blue smoke out of the breather pipe than out of the exhaust pipe. That generator sets at the bottom of the "to do" list, due to the condition it is in. If you have stuck rings I would think you would see excessive blow-by coming out of the crankcase breather.

I also picked up a 2.5LK at an auction dirt cheap. It smoked quite a lot, but did not foul the sparkplug. When I pulled it apart, the ring gap was a 1/4" (.250").

David C.
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