A little help here please

[wroughtn_harv]

My Miller Trailblazer with it's twenty horse Onan engine has got the punys, big time bad.

It's blowing oil up into the breather which gets into the carb and into the fuel oil mixture.

It only has less than eight hundred hours on the machine. I thought I had it figured out but that ain't working.

So bottom line what besides a hole in the piston is gonna create back pressure in the crankcase tough enough to blow serious oil up into the breather?

 

[bgott]

First I'd run a compression test. I don't know how many PSI to look for on that Onan but you need to see all of the cylinders within twenty percent of each other. If they're all the same but real low you might have collapsed the rings. Remove your cooling shrouds and see if there is dirt and stuff plugging the cooling fins. You might be running hot and pumping the oil through the rings. Also check your crankcase vent system. I don't know what they run on an Onan but if if it's not separating the oil vapor from the fumes being pumped out of the crankcase you're going to have a mess. All engines have blowby from the rings and combined with the pressure built up from the pistons doing their thing you can really pump some oil out if the vent is plugged. I've fixed a lot of supposedly bad engines by cleaning the vent system. Volvos were famous for plugging the oil/ vapor separator and having the same problem you're having. How is your oil level? If it has a manual fuel pump that has blown a diaphram you could be having gas get into the crankcase and over filling it. The excess has to go somewhere. Check your oil and if it is thin and smells like gas you've found your problem. Look at these things first and let us know what you find.

 

[boustany]

You may have a blown head gasket this can presurise the crankcase and lead to all kinds of problems. It all depends where the 'leak' is.
I had a Volvo with a weird problem once: it would crank real hard the first run rev if it had been left overnight, then work ok. Also, the rad kept boiling over 'cold'. I finally put 2 and 2 together when I smelled exhaust in the rad fill tank. Pulled the head, changed the head gasket with a pinhole leak from the cylinder to a water channel, and problem solved.
Had the same problem in my Case 15 years later.
If there is a pinhole leak between a cylinder and an oil channel you would burn a lot of oil, especially on start up.

 

[capt_ron]

wroughton_harv,
Correct me if I'm wrong but isn't this Onan air cooled?
I would imagine that it has a scored cylinder or piston problem.
Good Luck,
Capt Ron
PS: Do you do any Aluminum work using TIG. I need to find an affordable high frequency such as a Miller HF 15.

 

[mrcaptainbob]

Don't mean to talk simple to you, Harv, just don't know your familiarity with this, so I'll talk like you don't....Check the compression with all the plugs out. Spray a bit of oil (WD40 or 3in1 would be fine) in the plug hole and turn the crank a few times to spread the film. Check the compression again. If it's better, it's rings. How do the plugs look, by the way? If they're carboned up, you may just have sticking rings. If the oil level is good, and the compression 'changes' with the oil film, I'd give it a good dose of Parts Blaster. Work the pistons (by hand) a few times, especially with the plugs just "LIGHTLY" screwd in. The idea is to squeeze the Blaster juice into the rings. Loose plugs will prevent hydraulically seizing the engine or blowing a head gasket. Let the Parts Blaster do it's work overnight. Fresh plugs in the morning along with a fresh battery and gas and hopefully you're on your way. For all the help you give all of us, I hope that we can return the favor. Good luck, WraughtnHarv.

 

[wroughtn_harv]

Thanks for all the advice.

I have this theory about life and things. Nine times out of ten problems are little things or a chain of little things. It's rare that it's really a big thing.

But we do make them into big things sometimes I guess.

Today the puppy puked one more time. I hauled it a hundred miles to my bud's shop. I planned on leaving it and renting one until mine was fixed.

The ace mechanic that figured it out remembered a vary similar problem with Briggs and Stratton twins.

My oil dipstick was not making a seal. This allowed pressure to come into the crankcase which in turn was blown up into the breather soaking the filter and contaminating the income air with oil.

He said this has been a real problem on some motors.

We changed my dipstick assembly over to an old Onan system so the problem will not be mine again.

But someone could have sold me a rebuild or even a new motor and I would have paid the price.

So if you have a rider with an Onan or a Briggs twin and it starts blowing oil and smoking like a pot head trying to get rid of a stash, check the dipstick for seal.

 

[njrqs]

<font color=blue>smoking like a pot head trying to get rid of a stash</font color=blue>

/w3tcompact/icons/laugh.gif/w3tcompact/icons/laugh.gif/w3tcompact/icons/laugh.gif

Man your posts are often quite long and I struggle to get through them all but when I do, I always find a gem like that /w3tcompact/icons/wink.gif

Cheers

 

[mrcaptainbob]

Interesting find. As it turns out, I have a Kohler twin that's doing pretty much the same thing. I'll be checking that dipstick tomorrow. Thanks for passing that info along, WraughtnHarv.

 

[RidgeRunner]

Talk about sweet irony =)

When we 1st moved on to our "5 AC of Paradise" we had an old Craftsman 12 HP Rider. After being used as a bushhog and worse on our steep grades, it met it's demise. Appeared to have frozen pistons. Since it had been puchased used for $250 and I knew we needed something larger, I didn't even attempt to have it repaired.

Next purchased a used MTD powered by a Kohler V-twin. (Finally getting to the "irony" part, hang in there folks.) After just 2 months of the same tratment the Craftsman got, it started blowing oil and "smoking like a pothead."

I had had enough. Told CFO we were getting a "real" tractor if she wanted lawn mowed again, brush cleared, driveway repaired, etc. SOOooo, it appears after closer inspection that a leaky dipstick seal on a Kohler is a major factor in my becoming the doting father of a Kubota. SWEET!

Guess I'll replace dipstick, keep my mouth shut and hope CFO doesn't start reading Forum

 

[bgott]

Glad to hear A) you got it figured out. B) It didn't cost much to fix. Knowing the "pattern failures" of equipment beats the hay out of spending hours and dollars chasing your tail.