Mailing List lml@lancaironline.net Message #50798
From: Peter Hebert <pjhwfd@aol.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Crankcase pressurization
Date: Mon, 23 Mar 2009 12:59:30 -0400
To: <lml@lancaironline.net>
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Fred
I went through much of the same problems you are going through with my IO-550 Performance Engine in my Legacy. What works for me is An Andair oil separator pumped into the rocker arm cover.  This is the way Cirrus does  theirs.  we are looking for the lowest pressure on the return.  I also experimented with Where the crankcase vent in placed.  Higher out of the slip stream seemed better. I tried a collection container and it didn't work well for me. Would overload on occasion. Also my engine is very sensitive to oil level.  I run 6.5 and add .5 when it gets to 6.0. Lower levels with high AOA can froth the oil and send it out the breather.  Results may vary but this has worked for me.  Early on I was worried about ring seating but I'm sure that's not a problem after 250 hours. Oil consumption is a quart every 5 Hours.  Word has it that Performance skips the oil scrapper ring for better wear.  Can anyone confirm this?

Peter Hebert
444 Grey Birch RD
Stowe VT 05672
802-253-6816 home
802-279-6446 mobile


-----Original Message-----
From: Frederick Moreno <frederickmoreno@bigpond.com>
To: lml@lancaironline.net
Sent: Sun, 22 Mar 2009 4:13 pm
Subject: [LML] Crankcase pressurization

I wrote earlier that my IO-550 was dumping oil out the air oil separator, and with some fiddling with the plumbing, it appeared I solved the problem.   High power climbs yielded no oil loss.  Ground tests showed no blow by.  Problem solved. 
 
Wrong. 
 
New hypothesis: It appears that the losses occur during cruise, not take off and climb.   I climb at 160 knots, cowl flaps open.  I cruise at 200-220 IAS, cowl flaps closed.  The ram pressure at cruise is 1.5-1.7 times greater than in climb. 
 
So the current hypothesis is that the crankcase could be pressurized by external air pressure and the air flow through the crankcase carries oil overboard.
 
A bit of research suggests checking the crankshaft nose seal and the oil filler cap. 
 
Has anyone had problems with Continental crank case pressurization?  What have you learned? 
 
My next step is to pull the breather tube off the air oil separator and use some low pressure compressed air to pressurize the crankcase (engine off) and see if I can find some leaks.   The next level of complexity is to put a tube up the crankcase breather, connect to an airspeed indicator in the cockpit to check pressure, and go flying and see what happens.
 
Other suggestions or other experience that might help guide us through this maze?
 
Thanks in advance,
 
Fred Moreno
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