Breather Separators

Anyone have any pictures of the installation of an M20 Air/Oil Separator on a small Continental (65-90). Am going to be installing one on my C-90 and would love some advice, hints and pics if anyone has some....

Jeff, I have heard that it's not a good idea on our little engines (Lycs either). The reason is that the oil temp never gets hot enough to boil out the moisture (needs 200*, or better), and the separator simply dumps it back into the oil tank. I have had a couple of engine guys confirm my thoughts.

Is it for water or to keep you belly clean?

I think JR just wants to add another gadget to his plane....

I can give you the does and don'ts on the M20 for the C90. Plus a little theory on air/oil separators. I will get my pictures and post the rest. Trying to get the pacer ready for Sun & Fun and am pooped.

Hi,
Not the same, but had one on my Deb with a IO470. At 600hrs since freman it was a rust bucket inside. I had bought it at 500 hrs but it flew 100+ a year previously. It had a air/oil sep on it. When the new engine was installed we removed the separator and never looked back. I have heard other tales of similar happenings. In a cub it seems like just DDW or detrimental dead weight.

I don't use a oil separator on a small engine because it dumps so much water back in the engine. Just tie a plastic baby bottle over the end of the breather hose and you will see how much water that little engine is making. You may have to cut off the breather hose to keep the bottle up out of the airstream.

My understanding of the way an air/oil separator works comes from my Dad who is a mechanical engineer and worked for Cummins Engine Company until his retirement. When he was setting up test cells to test run engines they needed air/oil separators and he did a lot of research on them. The oil is never a vapor, therefore it is in little droplets (mist) suspended in the air coming out of the crankcase. When the oil droplets contact the fine screen in the air/oil separator it sticks to the screen and runs into the bottom of the separator and back into the crankcase. Water is a vapor in the air and it goes out the vent as a vapor. The stuff in the bottom of the baby bottle is condensed water vapor like what you get out of your air compressor. When the air is cooled the water in the air condenses forming water droplets Cummins used to run the engines on the test cell for 50 hrs. while dumping water into the engine every hour. There was never any water found in the oil, it vaporized as long as the engine was brought up to temp. Cars don't dump crankcase pressure overboard, it all goes back into the engine.

it vaporized as long as the engine was brought up to temp

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I have one C85 that the entire filler tube on the oil kidney is rust. It also runs very cool on the J3. It also had a separator on it. I don't think the water vaporised very good at 160 to 180 deg

Regardless, the baby bottle sure keeps the oil off the belly.

I have been thinking about using an air-oil separator also on my Cubs. I was about talked out of it , but now I'm not so sure. Has anyone tried feeding the output of the separator into a bottle temporally to see what is actually coming out that would otherwise go back to the oil sump? It seems to me that would settle it. ...Clyde Davis

So Steve, just to be clear, you're saying you think the M20 is okay for the Super Cub engines?

I had an M20, but didn't end up installing it when my mechanic balked at the idea. His additional point to the above discussion is that if you start to blow more oil than usual, that can be a useful clue that is masked by the presence of the air oil separator.

-->Aaron

That is why I started using the bottle in the first place. To see what and how much is coming out of the engine.

I have changed a lot of oil and never seen the stuff I have seen in the baby bottle or that is dripped on the hanger floor in the winter in the oil drain bucket.

The O-320 on 64M came into my possession with a 'separator' and an oily belly. Along with poor compressions, high oil temps and a thirst for oil.

After a rebuild it doesn't burn oil, run hot, or leave oil on the belly. Well, not much.

These aren't radial engines, after all.

I have had two experiences of the M20 making the problem worse than better, 135hp and 180hp lyc. I pulled it off my cub and life is good now.

sj

I put an air oil separator on an O-235. I started noticing condensation on the dipstick so I disconnected the drain line to the case and plugged it. I went and flew for about an hour. When I came back I drained what had accumulated. About a cup of water came out! I have since removed and stored my air oil separator.
Also about that baby bottle trick. Not wanting to degrade the supreme quality of my cub I went and bought a deluxe version with a rubber nipple and disposable liners. I cut the nipple so it was a nice fit over the breather line and off I went. Also at the same time I changed from 50wt to 30 wt oil for the winter. Went flying and came back with oil all over the side of the airplane so I started chasing oil leaks. I thought it was due to the thinner oil. After several flights and much oil wiping I found a cracked pushrod tube and a leaky valve cover. On the next flight there was oil all over the front of the engine apparently coming out of the front seal. All the oil leaks had been on the right side of the engine so that was where my concentration was. The clue light came on when I notice some oil on the inside of the left cowling lined up with the weep hole on the breather tube. I then realized the baby bottle was not vented and the weep hole was not big enough to properly vent the case so the case was pressurizing. What had happened was with only the weep hole providing the vent the case was pressurizing just enough to force oil out of every slight leak. When I sealed all the little leaks the last place for it to go was out the front seal. I then cut a half dozen holes around the perimeter of the nipple and flew with no oil leaks. I flew the baby bottle in the winter and noticed how much water it collected and I was worried it might freeze and block the breather so I removed it.
Moral of the story. If it ain't broke don't fix it. These planes have been around a long time so think twice about adding new gadgets. Weep holes are good!

As always, the input of the Learned Community has been very, very helpful. I've got some pitting from the long-term engine storage which has resulted in blow-by. Otherwise compression, etc. are all fine.

The cure is simple--cylinder overhaul/replacement, which is on my list of things to do when there is a bit more moolah in the till.

I thought in the interim that the M-20 might do the trick, but now am thinking differently.

Jeff, I built up a C90 for the Super Cub I fly with new cylinders, Divco overhauled the crankcase and Aircraft Specialties Services did all the internal steel. The engine still blew oil out the breather. The M20 helped a lot. Did everything to an O-290 trying to get it to quit blowing and nothing worked including the M20. On the 90hp SC I brought the vent elbow straight back and mounted the M20 just inboard of the filler neck. There is a plug in the side of the case that the oil can be drained back in by. I have seen people put air/oil separators on with a quick drain on them so they could drain the oil out rather than let it return to the sump.

Take a engine that has a lot of blow-by and take the breather tube and put it in a jar of water and watch it bubble. Now take the drain tube that comes off the separator and do the same thing. Same amount of bubbles. Now take the filler cap off and watch the oil fly out the filler tube. Pressure is the same at all three ports. The purpose of the breather tube is to relieve the pressure in the crankcase. A oil separator would sure work better if it were working across a pressure differential, but it isn't. You are betting on the air going through and the oil not. Could it be that it is also causing some added back pressure. Why not dump the breather back into a low pressure area like the intake.

Or, if you just want to keep oil off the belly and know what the engine is putting out, put a bottle on it or a cork in it.

If the oil separator were good science, all engines would have them. But, they are more like mother-in-laws. Some people like um and some don't.

I have had good luck on some airplanes by moving the vent tube as it exits the cowl. Some as little as an inch out of the sweet spot would blow oil all over. Some of the experimental and aerobatic guys vent it to the exhaust.

Cessna or Continental has a "mod" on the 0200 powered Aerobats for extending the fitting that the breather tube attaches to into the case an additional 1 & 1/2" or so, I don't have the exact length of this extension off the top of my head. This was to reduce blow by on the belly due to Aerobatic maneuvers allowing oil vapors to be sucked into the breather tube. http://www.cessna120/140.org/forum/files/breather_mod.pdf If this link does not work, there is supposed to be a line between breather and mod that does not appear, not a dash and I don't know what it would be called. Go to the 120/140 site for the info if interested. This mod worked well on my 0200/PA-11 even though I go inverted by accident only. Jim

Yeah, I think that's simply the brazed extension on the tube into the crankcase. Heard good things about that. Should be easy enough to do....

ON the small continentals I have had good luck with turning the crankcase breather fitting 180 so it points up, then run the breather line across the top of the engine then down. On a J3 it also helps keep that line from freezing up. If you can get one, use the 0-200 fitting.

Tried the brazed extension on one and it did help. But it had the vac pump gears in it. Took them out and it was lot better.

I saw a 206 here one year that had a tube all the way down the belly to the tailcone..... he said it was cheaper than a top overhaul .
JH

OK, so I bought an Airwolf air-oil separator and after Bob Eckstein looked it over and noticed that the spin-on oil filter adapter would have to be seriously moved to permit installation, I looked at the M20 (it is smaller), and it may work. Reading the comparisons made by Airwolf (http://www.airwolf.com/size_really_does_matter1.htm) I have decided I need a pretty good reason to install either the M20 or the Airwolf. Any new thoughts since 04/11/2007?

Thank you.

Randy

Randy,

Look in the member section in tech articles and find Vidir's breather design drawings. It's essentially a sophisticated baby bottle oil condenser with the addition of a drain valve. I started to make one but my plane doesn't drool enough to need it. The beauty of it is that it doesn't put the condensed spooge back into the crankcase.

I hope Vidir is doing well.

SB

Old thread resurrected. I just came across a breather oil condenser that I'd never seen before. No return line, no emptying it. Interesting.
http://www.aircraftspruce.com/catalog/eppages/superSlime2.php

stewartb said:

Old thread resurrected. I just came across a breather oil condenser that I'd never seen before. No return line, no emptying it. Interesting.
http://www.aircraftspruce.com/catalog/eppages/superSlime2.php

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Interesting idea of which I would like to know more of what is inside. This type of device would need to be installed in an area which is always warm. If not the oil could congeal blocking the breather leading to other problems. Those of you who operate in very cold locations should give this some thought before making the installation. Maybe a small electric heater?

I've had a breather outlet freeze over and would not want a repeat. It blew out the screwed in dipstick on a Lycoming 0-320 with ALL of the oil blasting out RIGHT NOW.

I put a Slime Fighter in an O-200 Cub and have been very happy with it. We used to have to pour the oil out of the snot bottle every few hours. Now it collects mostly brown water. I've got it in the breather line above the #3 cylinder. That gives it the right drain back angle and keeps it warm.