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Oil Weep/Breather Tube Poll

How should I cut my breather tube?

  • Cut a bevel like "A"

    Votes: 1 2.9%
  • Cut a bevel like "B"

    Votes: 3 8.8%
  • Bring the tube down straighter and cut a bevel like "C"

    Votes: 11 32.4%
  • Bring the tube down straighter and cut a bevel like "D"

    Votes: 9 26.5%
  • Leave it as is

    Votes: 5 14.7%
  • None of the above (explain below)

    Votes: 5 14.7%

  • Total voters
    34

alpinelakespilot2000

Well Known Member
I've been having some oil weep and oil usage problems with my Aerosport engine ever since new and I now have about 130 hours on it. Recently I checked with Aerosport on it and they recommended examining my breather tube to make sure the crankcase wasn't getting pressurized. I remember being very cognizant of this issue during installation, but I also remember seeing lots of different and contradictory suggestions for how to cut the end of the tube. Below is a picture of how my breather tube exists now as well as some alternatives. (If I recall correctly, the bend that exists in the tube coming from the firewall is how it came from Vans.)

2585hfp.jpg


Which way would you recommend I configure my breather tube to minimize any potential pressurization?

1. Cut a bevel like "A"
2. Cut a bevel like "B"
3. Bring the tube down straighter and cut a bevel like "C"
4. Bring the tube down straighter and cut a bevel like "D"
5. Leave it as is
6. None of the above (explain below)

Thanks for any help!
 
Last edited by a moderator:
flush on exhaust with hose

I used 8 inch of radiator hose and put it flush on the exhaust pipe. burns to contour fit.
 
Steve,

Is that a recent picture, or one from your build log? If it's not a recent pic is there any oil residue on the pipe?

Mine doesn't come straight down, it bends slightly forward. The cut is somewhere in between C and D, leaning slightly towards D. I burn about 1 quart in 25 hours.
 
Take a look.

Look at the termination of your exhaust pipes relative to the air flow going past them. This helps pull the gases out of them. The cut to you breather can use that same effect to help pull crank-case gases out too. I think that looks like "C" in your pictures to me. Hope this helps.
Yours as always R.E.A.III #80888
 
I used more like "C" and also drilled a hole in the tube about 4-6 inches up, then took a screw driver and stuck it in the hole and pulled that screw driver up to the vertical to kind of elongate the hole.

That hole now has any airpressure from within the cowl to push residue oil out of the end of the tube and in if any moisture keeps the end warm.

At least thats my story :D
 
AeroSplat air-oil seperator w/ vacuum system

+1 Eventually you will save enough on oil to pay for it.

Larry Tompkins
544WB -6A
W52 Battle Ground, WA

Get the reed valve and saddle clamp from anti-splat and the belly will be dry!
 
Steve,

Is that a recent picture, or one from your build log? If it's not a recent pic is there any oil residue on the pipe?

Mine doesn't come straight down, it bends slightly forward. The cut is somewhere in between C and D, leaning slightly towards D. I burn about 1 quart in 25 hours.
Yes, this is an old pic taken during initial installation, but its still positioned the same way right now. I do get a bit of oil out of the tube and on the exhaust but I don't know really how much is coming out. Right now I seem to be losing a qt per every 7-9 tach hours or 10-11 Hobbs hours. Not sure if the engine is leaking it, burning it, or losing it out the breather.
 
A or D.

If your engine has blowby (they all do to some extent), it will overcome the very low resistance of the airstream and the breather will function as designed. You will not overpressurize the crankcase and blow out the crankshaft nose seal.

Originally I cut mine like "C". You got to read about that ~12 years ago in the RVator. Cutting it like C creates a vacuum, and if you are careless to not tighten the dipstick, that suction is happy to draw a lot of air through your crankcase, taking a lot of oil mist with it. My engine blew over a quart of oil out it on a 15 minute flight, as a result of the "C" cut and the loose dipstick. That kind of thing could ruin your whole day on a 1 hour flight.
 
Interesting... no real consensus so far in the polls.

Regarding the few comments about going with the anti-splat oil separator...
Is installing one of these just going to reduce the potential for oil on the belly or is it also likely to address the issue for which I started this thread, namely the weeping oil (from many places on the engine) that might be the result of my breather tube causing pressurization in the case?
 
The top two engine shops down here would recommend not to fit air oil separator devices unless there is a 100% guarantee zero moisture return. Their experience is that a lot more water ends up inside those engines and it keeps them in premature rebuild work.

They also do say that they should recommend them, with a huge grin on their faces. :D
 
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