PT425 and Robin/Subaru Engine Oil blow-by

[atwood]

I'm having an oil blow-by issue with the Subaru EH-72. For sometime now I've been getting engine oil collecting on top of the carburetor inside the air filter. The engine generally runs fine except the oil sprays out of the carburetor and collects on the intake manifold and everywhere else. I asked a local repair shop to look at it and they pulled the engine, cleaned up the mess, pulled the fly wheel, checked compression in both cylinders (175 psi), pulled the head, cylinder walls looked great, no marking, etching (500 hours). Checked the crank case check valve, okay. Replaced hoses on oil cooler, which had been leaking, replaced oil, filter, plugs, fuel lines, just about everything, looked almost new when finished. Ran it yesterday cleaning up some snow and splitting wood. Runs great, still leaking spraying oils out of #1 cylinder. Anybody have any ideas? I've talked with Terry and tech guys at Robins/Subaru, all seem stumped. The one thing that was not done was a leak down test and the shop did not tear down the pistons to check rings. Thanks for any insight and/or experience.

 

[cqaigy2]

Too much oil in crankcase pushing out of the pcv into the intake, running the engine upside down, um, I've run out of ideas.

 

[MossRoad]

Incorrect dipstick?

 

[MuncyBob]

You are experiencing the exact situation I have had since last spring. See the thread:
http://www.tractorbynet.com/forums/power-trac/327719-im-without-my-422-awhile.html

Both cylinders failed leak down test. I eventually was getting so much oil that air filter was getting clogged and I was losing power. Currently waiting for heads to be reworked and new guides installed, then valve job. From what I have learned this is a heat related issue. I'll be making several mods when I finally get my PT back.

 

[atwood]

Thanks Farmall140. I did read your thread and at first, thought that your engine issues were similar to mine, which it might be? With mine all seems good, runs good, etc except for the oil blow-by. The mechanic didn't perform a leak down test only a cylinder pressure test. I'm going to take it back in for the leak down test and go from there. He did adjust the valves and indicated only one was out. I guess as MossRoad indicated as well as ccraigy2 too that it could be too much oil in the crank case and maybe the engine was assembled with the wrong dipstick 10 years ago? Worth checking it out. Thanks and Farmall140, hope your machine gets up and running soon.

 

[Kent]

Interesting article on oil blowby in motorcycle engines, which points to engine design and rings being the problem:

http://www.motorcyclecruiser.com/understanding-blowby-motorcycle-engines

 

[J_J]

I would think the breather tube would be the source of the oil.

The carb has a one way path.

The piston would shove the oil in the combustion chamber.

The oil capacity of that engine is .41 gal.

I am not sure that includes the oil filter though.

If your oil/fluid volume is more, the you might have some gas mixed in from a leaky carb

 

[atwood]

Thank you, all good points and good article. Sure do appreciate your comments. Haven't seen any gas in oil. Perhaps it is a bad ring, will hopefully find out with leak down test. J_J by the breather tube do you mean the tube coming from the OHV into the air filter plate/carb? The mechanic did replace breather and breather gaskets (2). Over the years, I've never noticed a the oil level to be high on the dip stick and don't remember how much oil I've added when changing the oil and filter. I guess something to pay closer attention to.

 

[J_J]

Yes, the crankcase breather tube to the carb.

 

[MossRoad]

I had some issues with a tube (not sure of its function; its about a 3/8-1/2" tube) on my Kohler a few years ago. It is supposed to be exiting directly next to the throat of the carb. Somehow it popped out of its bracket and move several inches away. The motor was running very rough and I had some oil in the breather. Buy sheer luck, I moved that tube towards the carb while running and the roughness went away. Moved it away and it came back. Found where it was supposed to be and locked it down better.

So, even though you are having oil in your breather, are you using excessive oil during operation? How often do you have to add engine oil?

 

[woodlandfarms]

stupid question but has your property changed? are you tilting the engine more than you have in the past? And your PT, it is a verticle engine, correct?

 

[atwood]

My property is still the same, hilly West Virginia. Other than sometimes going up and down vertically some steep hills I typically keep the 425 on gentle slopes. I should note that this blow by in the air filter has been going on for sometime now , perhaps several years. I had mentioned it to the mechanic/friend I know over that period but since it was running okay he didn't have any concern or idea why it was happening and I just kept running it, adding engine oil here and there not really paying a lot of attention. However this past summer when outside temps were higher cutting grass, brush cutting, etc, the oil residue was burning off the outside of the engine. That could of been the hose on the oil cooler that had worked loose but either way after more inspection I decided that I should pay some long overdue attention to the problem or find out the cause.

 

[woodlandfarms]

Well, a steep slope can cause oil to get into the carb. You say this has been going since the beginning. I am not saying it isn't your engine, but I am wondering if you are pushing the machine further over the edge as you have become more comfortable. That, and maybe your oil level is too high to begin with.

The thing that is odd is that your compression is still solid. A leakdown test would be a good double check but.

 

[MossRoad]

Whats the difference between a compression test and leakdown test and how are they performed?

 

[ponytug]

I'm sure you have thought of it, but if the oil level is even a little too high, there will be splashing and foaming, which will raise the oil level higher, resulting in more foaming and higher oil levels... The end result will be lots of oil spray out your breather tube. It is also hard on your crankshaft and connecting rods to be slapping oil.

Foamy oil isn't a great lubricant, either. Think of it as oil with 20% of the good stuff and 80% bad stuff (air).

Just a thought.

All the best,

Peter

 

[woodlandfarms]

As I am no mechanic, I was told a compression test was a quick turnover of the engine and guaging what the pressure was.

Leakdown was to get the piston into TDC or as close as possible and wait for X time to see how much pressure escapes.

But heck, what do I know. It always sounded basically the same to me.

Knew I would find it.

Compression-leakdown test

 

[MossRoad]

Thanks for the link!

 

[atwood]

Thanks everyone. yes, from what I've been told the leak down test is more involved than the compression test like Woodlandfarms indicated. And maybe the steeper slopes have something to do with the blow by, it surely is possible. I did take the 425 back to the mechanic and this time, not only the blow by (very little) but more oil was over the bottom of the tub on the oil cooler side. He put some dye in the oil and seems at this point more is coming from the oil cooler area. He is going to pull the engine and run it on the bench to get a better look. Wherever its coming from the flywheel seems to blow a bunch around. Other than that the engine runs probably better than it ever has or at least for a long time. Will let you know what he finds.

 

[arrow]

Whats the difference between a compression test and leakdown test and how are they performed?

Basically Moss, compression reads just pressure on it's gauge and just begins to tell the story. Sort of reading the book flap to get the gist of the book. A leak down reads percent of leakage. Leak down is more for chasing down where the leak is as air is fed into the gauge adapter and seeing where it exits. If air is coming out the PCV valve for instance, you have a bad piston ring. Coming out of other areas describes if you have a cylinder head or valve leak etc.. Both gauges are inserted into the empty spark plug hole. The only thing that the compression gauge reads is what is being created by the piston. The leak down gauge is fed air or sometimes nitrogen. It is zeroed and then air is blown in which is then dispersed within the engine cylinder to measure first a leakage percentage and then where the leak is as the air attempts to find the least resistive path for exiting.

 

[Frank Sorbello]

I too was having problems with gas in my oil. I put a shut off valve on the fuel line before the fuel pump. Whenever i am done with my PT-422 for the day I shut the valve off. My oil has been good ever since I started using the shutoff valve.