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?