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Breather run into exhaust (warning)

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gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Wed Jun 06, 2007 12:04 pm Post subject: Breather run into exhaust (warning)

One worry is that valve fails closed and cause the crankcase seals blow. That could be very critical and losing the front crank seal could cause fire, loss of oil pressure (engine power) and loss of visibility out the wind screen. It has happened, not with a drag race crankcase evacuation valve, but from a blocked breather. 

   

  If you use this system put a "whistle slot" into the tube. It is a slit along the length in the rubber tube (a few inches) that is just held close by the natural shape of the tube. If you get a blockage and pressure build the slot will open up enough to allow some pressure to escape. 

   

  I think running the breather near the hot pipe, but outside works fine. This is standard procedure on RV's. I usually transition the last few inches from rubber to metal to sit next to the hot pipe.

   

  Also if the suction is too great it  can suck out more air and oil  desirable. When using the technique of burning the breather air/oil on the out side of the pipe, it is recommended you cut the end of the tube at an angle into free air stream. If you have air going across a flat tube or angled down stream you can really cause excess suck on the breather and pull oil out of the plane.

   

  This 

  >>>>>> \|

   

  Not this 

  >>>>>> |/

   

  However the drag race set up has you angle the air down stream. That may cause lots of suction but if the valve regulates the suck that is fine but as I say if that valve fails closed it could be bad news with out a whistle slot in the hose. 

   

  Cheeres George ATP/CFI-II-ME



        Ready for the edge of your seat?  [url=http://us.rd.yahoo.com/evt=48220/*http://tv.yahoo.com/]Check out tonight's top picks[/url] on Yahoo! TV.     [quote][b]

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rv9jim(at)juno.com
Guest

Posted: Wed Jun 06, 2007 12:55 pm Post subject: Breather run into exhaust (warning)

George, 

        What you are saying on the breather tube is to cut the end such

that a slight pressurization occurs rather than a slight suction on the

end ???   If the tube is inside the cowl, will it make a difference? 

Mine is exiting just in front of the engine mount for my "9-A" (tie

wrapped to the mount) and about 1/4" above the exhaust pipe. The end of

the tube is sort of angling toward the rear of the a/c.



Jim

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n801bh(at)netzero.com
Guest

Posted: Wed Jun 06, 2007 2:24 pm Post subject: Breather run into exhaust (warning)

You probably have this envisioned incorrectly. The valve is a high temp metal check valve to prevent a flame from traveling back up into the crankcase during a major backfire in the exhaust pipe. As long as the engine is running there will ALWAYS be suction through the valve and vent system. I believe you think at some times there is pressure traveling up the vent line,,, there isn't during normal running. One poster said all he did was weld a 1/2" stainless tube to the exhaust pipe and didn't even use a valve, I hope he chimes back in to report that in that configuration he has experienced no issues with lighting off the vapor coming from the crankcase. Mike did contact me through my website asking for my extra valve but once I explained they are available at any speed shop in most towns he elected to take a few minutes to buy one locally. By doing that he will end up with two valves and he and a buddy will be all set up for less then 17 dollars each. Small price for a sure fix to a dirty oily belly. By just mounting your vent line close to the tail pipe you get the benefit of burning off some blowby oil but some will still get on the belly and you don't get the positive vacuum that a crackcase evacuation system creates. To answer the question of how much vacuum is produced,  during initial testing on my plane I have seen 16 inches of vacuum during full power on takeoff. My motor is a 347 cu in but I do turn it 4500 rpm during the climb. I am guessing a 320/360 cu in Lyc (at) 2700 should produce at least 10-12 inches, way more then enough to draw crankcase pressure from your motor.IMHO 

do not archive 

Ben Haas

N801BH

www.haaspowerair.com

-- <gmcjetpilot(at)yahoo.com> wrote:

 One worry is that valve fails closed and cause the crankcase seals blow. That could be very critical and losing the front crank seal could cause fire, loss of oil pressure (engine power) and loss of visibility out the wind screen. It has happened, not with a drag race crankcase evacuation valve, but from a blocked breather. 

 If you use this system put a "whistle slot" into the tube. It is a slit along the length in the rubber tube (a few inches) that is just held close by the natural shape of the tube. If you get a blockage and pressure build the slot will open up enough to allow some pressure to escape. 

 I think running the breather near the hot pipe, but outside works fine. This is standard procedure on RV's. I usually transition the last few inches from rubber to metal to sit next to the hot pipe.

 Also if the suction is too great it can suck out more air and oil  desirable. When using the technique of burning the breather air/oil on the out side of the pipe, it is recommended you cut the end of the tube at an angle into free air stream. If you have air going across a flat tube or angled down stream you can really cause excess suck on the breather and pull oil out of the plane.

 This 

 >>>>>> \|

 Not this 

 >>>>>> |/

 However the drag race set up has you angle the air down stream. That may cause lots of suction but if the valve regulates the suck that is fine but as I say if that valve fails closed it could be bad news with out a whistle slot in the hose. 

 Cheeres George ATP/CFI-II-ME

  Ready for the edge of your seat? [url=http://us.rd.yahoo.com/evt=48220/*http://tv.yahoo.com/]Check out tonight's top picks[/url] on Yahoo! TV. [quote]

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[b]

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klwerner(at)comcast.net
Guest

Posted: Wed Jun 06, 2007 2:41 pm Post subject: Breather run into exhaust (warning)

I don't see how a vacuum created by  the hot exhaust gasses could block the breather tube. Nor  should an exhaust generated vacuum be able to pressurize the  crankcase...

  

 Granted, there were incidents where  the end of the breather stuck out in the cold below the cowling and froze shut,  causing a pressure buildup inside the case, which a whistle slot in a warm  location will prevent. 

  

  Oil loss *may* need to be  addresses on any individual engine by regulating this crankcase vacuum  depending on its health, but if the piston rings seal well, then there should  not be to much blowby anyway.



 [quote]   ---

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klwerner(at)comcast.net
Guest

Posted: Wed Jun 06, 2007 2:44 pm Post subject: Breather run into exhaust (warning)

Jim,

 You should be ok with this setup. You  should see a slight vacuum on its end. Do you also have a small whistle slot in  the tube? You may not need it if your tube ends inside the warm cowling exhaust  air.

 [quote]   ---

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PittsS1(at)aol.com
Guest

Posted: Wed Jun 06, 2007 3:18 pm Post subject: Breather run into exhaust (warning)

you guys make this so difficult ... hang around the acro guys, this isnt  new to them nor is it rocket science.

  

     mike



See what's free at AOL.com. 

  [quote][b]

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klwerner(at)comcast.net
Guest

Posted: Wed Jun 06, 2007 3:40 pm Post subject: Breather run into exhaust (warning)

Mike,

  

 I totally agree with you!  Why reinvent the wheel  that the acrobats use already...     do not  archive

  

 [quote]   ---

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