Oil from breather tube
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R44inCincy
Member Since : 2011
Posts(40)
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Oil from breather tube

02-18-2014 07:32:16

Here's the standard, "My helicopter is leaking oil, is it normal or abnormal" question. 2006 Raven II that always runs pretty clean. After the last 4 flights, I've noticed more oil than normal (I think) under the ship, right under the breather tube. It's not a lot, but more than just a drop or two.

On the last flight, I saw oil bubbling out the bottom right after shutdown (see pic).

So, am I being paranoid or is this something to look at? No oil on the inside of the engine compartment anywhere, temps are normal, etc. Outdoor temps have been very cold.

Thoughts?

Oil from R44.jpg

Replies

MVH-DOM
Member Since : 2013
Posts(63)
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02-17-2014 10:38:57
This is normal, remember this tube is a crankcase vent.  It has to vent the pressure from the crankcase created by the blow-by of the piston rings.  If this vent was not there or frozen over, the pressure will build and push out the crankshaft seal.  What is normally seen coming from the breather is more water than oil (usually), this is the water that has formed in the engine due to heating-cooling-heating-cooling (condensation).  Once you have flown the aircraft that water that was in the oil is boiled off and makes it way out of the breather tube as steam (if you have ever watched a Robby in the hover on a cold day, you can actually see the steam coming from out the vent tube), once you shut down and the temperature drops, any water moisture in the tube will turn back to water and flow down the tube and end up on your hanger floor in a little puddle about the size of a post-it-note.  If you look at that puddle you will see it is mostly water with some oil mixed in.  There is some splash lubrication going on inside the engine so some oil will go out the breather tube as well.  If you over fill the oil, the engine will blow what it doesn't want out of the breather as well.  It looks like from the pic, that its an icicle that is hanging from the breather.  This is also why the two holes are drilled in the breather tube near the bend, in case the outlet becomes frozen over, the engine will still vent.  Keep an eye on it and your oil consumption, but I am willing to bet your engine is behaving normally.
Hope this helps.
13snoopy
Member Since : 2007
Posts(339)
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02-20-2014 03:21:21
This is normal, remember this tube is a crankcase vent.  It has to vent the pressure from the crankcase created by the blow-by of the piston rings.  If this vent was not there or frozen over, the pressure will build and push out the crankshaft seal.

I disagree. Normal Lycoming crankcase pressures are 0 to 1.5 inches of water. Zero inches being measured in normal in cruise flight.  A common misconception is that engines build up extraordinary crankcase pressures. Healthy engines do no such thing. There is obviously some oil getting discharged via the vent, but its not the result of high crankcase pressure.
A stopped up breather pipe on a healthy Lycoming engine would not result in the crankshaft seal getting blown out, either.
The engine powering the R44 Raven only revs to about 2,600 to 2,700 RPMS or so. This is a large, slow running engine that ostensibly would not produce high crankcase pressures when healthy.
We are not talking about a 10,000 plus RPM engine that boasts compression ratios of 12 or 13-1.
MVH-DOM
Member Since : 2013
Posts(63)
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02-20-2014 08:21:19
Actually, yes it will, I have seen it, I have repaired it (not on a Robinson, yet).  If the pressure is not there or not to worry about, then why install a breather pipe in the first place?  Blank off your breather pipe completely (as well as the whistle holes inside the cowl) and see what happens.  All piston engines have blow-by (its inherent by design).  Next time you do a compression test at your 100 Hr Insp, remove the oil dipstick and observe how much air is actually heard escaping from it.  If the piston rings have happened to line up their gaps (which they will do), it can be quite noticeable.  As for the crankshaft seal (on a Lycoming) there is no actual physical means of holding the seal into the crankcase (other than then by one of the approved adhesives, such as Pliobond)  when compared to some models of Continental engines that have plates holding the seal in.  Without the breather pipe, the only other place the pressure can be relieved is by blowing by the seal or forcing it out.

Please find a copy of a book called The Lycoming Flyer Key Reprints, read the article on page 24 (The Whistle Slot), it deals with what you say "can't happen".  I am familiar with your quote, it comes from the Sacramento Sky Ranch Engineering Manual ( an excellent  book, too bad they closed up shop recently), however they are not the manufacturer.

SN, I know you don't like me and disagree and argue with everything I post.  My knowledge comes from 20+ years as a licenced AME in Canada and 5 years instructing in aircraft maintenance at SAIT.  I have maintained Robinson products for the better part of 10 years in the Canadian north where the R22/R44 is operated to its maximum limits (phone Pat or Daniel at RHC, ask them how hard their products are operated in the Canadian oilfields, mention me, they know me.)( I think the tuna boat Robbies maybe operating in a harsher environment)  The rest of my experience comes from working on radials on spray planes to flying school 150's to pressurized turbo props and warbirds.  I am currently the Director of Maintenance for an RHC Service Center where I maintain  6 R22's & 7 R44's.  I actually do know what I am talking about.

R44inCincy, your bird is fine, your A&P will tell you the same thing.

Blue Skies
rotormatic
Member Since : 2010
Posts(42)
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02-21-2014 07:22:29
NATIONAL TRANSPORTATION SAFETY BOARD
WASHINGTON, D.C.

ISSUED: February 8, 1984

SAFETY RECOMMENDATION(S)
A-84-10 and -11

On February 2, 1981, about 17 minutes after takeoff, a Piper PA-28R-201, N4542Q,
crashed into a wooded area near the Houghton County Airport, Houghton, Michigan. The
pilot and two of the passengers on board the airplane were seriously injured. One other
passenger received minor injuries, and the airplane was destroyed. The weather at the
time of the accident was 2,000 feet overcast, 1/4-mile visibility with light snbw, and a
temperature of minus 5' F.

While in flight, the airplane's engine stopped suddenly. The investigation disclosed
that the stoppage was the consequence of oil starvation.

The investigation into the cause of the oil starvation revealed that the front
crankcase oil seal for the crankshaft was displaced outward. It was found also that the
crankcase breather line contained several pieces of ice about 1/2 inch in diameter. It was
concluded that the crankcase breather line had been blocked with ice, which resulted in
excessive pressure in the crankcase. The excessive pressure displaced the oil seal and
forced the oil overboard.
13snoopy
Member Since : 2007
Posts(339)
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02-21-2014 07:25:12
Actually, yes it will, I have seen it, I have repaired it (not on a Robinson, yet).  If the pressure is not there or not to worry about, then why install a breather pipe in the first place? 

SN, I know you don't like me and disagree and argue with everything I post.

Exaggerate much? I have only replied to you in one other thread. And it was in that thread that YOU began by talking about how I "couldn't afford" a helicopter.
So it seems like it is you with the problem, not I.
And it's easy to diagnose your problem: you go nuts when anyone dares to dispute your word.
You remind me a lot of another poster who spent most of his time telling us all how much of an expert he is at everything.
Google Cliff Clavin, there's probably a picture of you beside the name.
13snoopy
Member Since : 2007
Posts(339)
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02-21-2014 07:27:00
NATIONAL TRANSPORTATION SAFETY BOARD
WASHINGTON, D.C.

ISSUED: February 8, 1984

SAFETY RECOMMENDATION(S)
A-84-10 and -11

On February 2, 1981, about 17 minutes after takeoff, a Piper PA-28R-201, N4542Q,
crashed into a wooded area near the Houghton County Airport, Houghton, Michigan. The
pilot and two of the passengers on board the airplane were seriously injured. One other
passenger received minor injuries, and the airplane was destroyed. The weather at the
time of the accident was 2,000 feet overcast, 1/4-mile visibility with light snbw, and a
temperature of minus 5' F.

While in flight, the airplane's engine stopped suddenly. The investigation disclosed
that the stoppage was the consequence of oil starvation.

The investigation into the cause of the oil starvation revealed that the front
crankcase oil seal for the crankshaft was displaced outward. It was found also that the
crankcase breather line contained several pieces of ice about 1/2 inch in diameter. It was
concluded that the crankcase breather line had been blocked with ice, which resulted in
excessive pressure in the crankcase. The excessive pressure displaced the oil seal and
forced the oil overboard.

No mention of time on engine. This was only 35 years ago... ::)
MVH-DOM
Member Since : 2013
Posts(63)
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03-04-2014 02:02:03