REFLECTOR: Breather tube

[Grover McNair]

I am not familiar with the BMW system but I bet they were not providing
enough negative pressure to the crankcase. Venting to the atmosphere would
have been the easy fix.

The only down side of venting to the intake is that some oil is burned with
the intake charge. Deposits can build up in the combustion chamber. This
usually only happens on older engines where the rings are worn and crankcase
pressures are higher.

Grover 

 

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of John Dibble
Sent: Friday, March 02, 2012 1:19 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Breather tube

 

I thought PCV did create a little crankcase pressure.  My 1975 BMW
motorcycle had that feature and they forgot to redesign the main seals for
the higher pressure and I had problems with leaks.  I solved the problem by
removing the PCV device and just venting to the air.  As was mentioned, the
main thing is to have adequate ventilation to avoid engine oil leaks.  As
your compression leak increases with age, more venting will be needed.

John

On 3/2/2012 11:54 AM, Grover McNair wrote: 


Positive crankcase ventilation, that is applying vacuum, has been shown to
increase horsepower marginally. This came about in the late 60’s when pcv
systems were first used on cars to reduce emissions. I agree with Scott, The
last thing you would want to do would be to pressurize the crankcase by
pointing the tube forward. Negative pressure is best. 

Grover McNair 

  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Ruben Creus
Sent: Friday, March 02, 2012 11:55 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: REFLECTOR: Breather tube 

  

I had to temporarily remove the breather tube the other day to work on some
wiring stuff. When I place the tube back in place and looking at it,  I
thought that as the tip of the breather tube that exits the cowling is cut
in a 45 degree angle, then I assumed that if I place it facing the nose I
guess it would have air pressure pushing into the tube. If I place it facing
the tail, then the air around the tube it might create low pressure and
therefore pushing the air out of the tube creating suction. If I place it
facing the wing, the air would just travel passing the tube with no effect. 

  

I guess all this rational also depends on the air pressure inside the
breather tube coming from the engine, so I did several tests, facing the
tube in this three positions and flying a bit. My tests concluded that when
the tube is facing the tail It seems I have more oil coming from it as the
cowling seems more oily , but is was hard to conclude as the oil leaving the
tube could end up how knows where. And where the tube is facing can also
impact where the oil will eventually go. Showing all my test were kind of
inconclusive. 

  

So, guess the main question is that if you know what is the proper
positioning of the 45 degree opening, nose, side, or tail, or if it really
matters? 

  

  

Ruben G. Creus 

Ë +1.571.215.0025 

*    <mailto:ruben at vainneg.com> ruben at vainneg.com 

  

  

  

  

  

  

  






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