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Onan B48 On Gt18 Slobbering Oil From Exhaust

sears gt18 onan b48

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#1 Utah Smitty OFFLINE  

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Posted June 02, 2012 - 10:58 PM

Well, it never seems to end. I just got the mower deck installed on mom's tractor and she reported it wasn't running right... didn't have enough power to run the deck.

I went up today to check out the engine. First thing I did was change the oil. Then I started it... the front cylinder seemed to be "puffing" and the power was definitely off.

I wanted to make sure the problem wasn't i the deck, so I released the deck drive lever and shut off the engine. I kept the deck brake rod out so I could turn it;... turned freely with no problems.

I mowed quite a bit with it, but I had to keep it in 1st or 2nd Low Range and take cuts that were only half the width of the deck.

It was after about an hour of this that I noticed oil dribbling out of the front muffler.

I'm not real familiar with the Onan, but I have had a couple flat twin B&S apart and I assume they are the same.

I'm thinking I have a broken ring... any other input out there? Also, advisability of rebuilding the engine versus repowering... maybe with another brand... I have a good running 18hp B&S flat twin...

Thanks in advance,

U.S.

#2 KennyP OFFLINE  

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Posted June 03, 2012 - 04:15 AM

How much did you run this before the deck was put on? Could it possibly be 'stuck' rings? Did it sit for quite some time?

#3 JDBrian OFFLINE  

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Posted June 03, 2012 - 05:56 AM

It's funny the oil is running out and not being burnt. Not being familiar with that engine i can't help much. I know that in a Subaru boxer engine sometimes the rings can get aligned with the gaps at the bottom making the engines burn oil. Eventually this usually rights itself but can lead to high oil consumption. Perhaps that cylinder is not firing and the oil that normally would be burnt is being expelled. Have a look at the plug and see if it's fouled and if you have good spark on that cylinder.
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#4 timtractor OFFLINE  

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Posted June 03, 2012 - 07:43 AM

I would say the first thing is to take a compression check. That will show you if it is the rings or piston problem.

The other possibility cound be is that you have a bad valve guide. But I would lean toward the ring on the piston.

What happens is the oil piston ring either breaks or weakens. This allows the oil from the crank case to enter the cylinder. If the problem is bad enough the cylinder then becomes more of a pump for the oil and discharges it wherever it can, while the other cylinder keeps running. That could be why you only see it out of only one exhaust.
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#5 MH81 ONLINE  

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Posted June 03, 2012 - 07:49 AM

U.S., sorry to hear it. Sounds like you may be trading Mom Mowers for a while.

I will second the oil ring issue as a probability, but wonder how it could be running with that much oil. As mentioned above, it it firing on both?

#6 olcowhand ONLINE  

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Posted June 03, 2012 - 10:11 AM

Take the air filter off to see if the oil is coming from the crankcase breather tube. I changed the oil in my 18hp B48 Onan last year, then immediately had BAD smoking and oil coming from the exhaust. It was coming up my breather tube. I had my oil level a bit high. Not enough that I thought it would be a problem, but it sure was! Dropped the level & all was fine!
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#7 olcowhand ONLINE  

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Posted June 03, 2012 - 10:18 AM

OH....and check that your dipstick seal plug is in good shape. If it lets air in it can cause more air volume to go through the breather tube, carrying oil as it goes.
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#8 Utah Smitty OFFLINE  

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Posted June 04, 2012 - 10:40 PM

U.S., sorry to hear it. Sounds like you may be trading Mom Mowers for a while.

I will second the oil ring issue as a probability, but wonder how it could be running with that much oil. As mentioned above, it it firing on both?


It appears to be firing on both cylinders. The exhaust is hot in both mufflers... I suspect it's leaking past the rings... I guess I need to pull the head off and see if the cylinder is scored...

#9 olcowhand ONLINE  

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Posted June 05, 2012 - 01:56 PM

But did you check to see if it's coming up the breather tube? Don't tear into it until you do.

#10 Utah Smitty OFFLINE  

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Posted June 05, 2012 - 11:11 PM

But did you check to see if it's coming up the breather tube? Don't tear into it until you do.


I'll check that. Before I ran it, I noticed the area on the air filter housing where the breather tube pushes in had a small amount of oily residue--about the size of a dime. I didn't check it afterwards, but I will.... Thanks for the info.

U.S.

#11 coldone OFFLINE  

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Posted June 06, 2012 - 05:24 AM

But did you check to see if it's coming up the breather tube? Don't tear into it until you do.



Ditto!!!! I chased a similar problem, had oil in the breather. I thought it was everything else, bought alot of parts that didnt fix it. I finally gave the rubber stopper a few wraps of electrical tape, no more oil in the breather!

#12 Utah Smitty OFFLINE  

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Posted June 17, 2012 - 03:13 PM

Well, I went and got the tractor yesterday. It started up, but was missing and didn't have the power my other GT18 does. I got it up on the trailer, and took a picture of the exhaust manifold.

2012-06-17_13-54-32_789.jpg


The oil level is correct--I changed the oil on it when mom said there was a problem with it, but the problem remained. I also checked the dip stick seal--it's okay as well.

I'm thinking I have a scored cylinder or stuck rings. Problem is, I don't know what brought it on. I changed the oil and cleaned out the fins on the cylinders when I bought the machine (there were a couple mouse nests on the underside behind the shrouds.). I also cleaned out the carburetor and ran some Sea Foam through it. It ran fine at that time and for several weeks afterwards.
I'll pull the cylinder hear and measure the bore--anyone know if new pistons and/or rings are available and what they might cost.

OTOH, I have an 18 hp B&S flat twin with the same shaft size, height, and bolt pattern--I think it might fit up there--has anyone done this conversion..

Thanks for your input--this forum is one of the most informative I've ever known.

Regards,

U.S.

#13 olcowhand ONLINE  

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Posted June 17, 2012 - 03:55 PM

Early style, which is likely yours, around $110 for a piston kit with piston, ring set, wrist pin, & circlips. Std ring set only is around $22....plus shipping. All readily available.
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#14 Utah Smitty OFFLINE  

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Posted June 18, 2012 - 12:50 PM

Early style, which is likely yours, around $110 for a piston kit with piston, ring set, wrist pin, & circlips. Std ring set only is around $22....plus shipping. All readily available.


Thanks for that info. OCH... I was thinking it would be more expensive than that. The tractor was made in 1978. I have the engine s/n as well...somewhere. I can always get it again off the fan shroud.

I'll just add it to my list of things to get done before I die... at the rate, I'll live forever!!!!!

#15 Utah Smitty OFFLINE  

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Posted June 21, 2012 - 10:33 PM

OKAY!!! I finally found out what was causing the oil slobbering... you'll never guess what it was... in fact, let's make a game out of it...

Anyone care to hazard a guess what caused it?

(Hint: The fix cost about $5, and, I got it fixed in about 10 minutes. Also, none of the suggestions above were correct)

Edited by Utah Smitty, June 21, 2012 - 10:33 PM.





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