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Oil in sump

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Speedy11(at)aol.com
Guest

Posted: Mon Apr 19, 2010 1:12 pm Post subject: Oil in sump

Engine Experts,

 I have a Barrett IO-390.

 When I removed one of the intake pipes from the sump to the cylinder  the other day, the sump had oil in it.

 Should the sump where the intake pipes insert have oil in  it??

 If so, how much is permissible?

 Stan Sutterfield



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MONTY(at)bpaengines.com
Guest

Posted: Tue Apr 20, 2010 7:50 am Post subject: Oil in sump

It is common for some oil to be in the  plenum.  The sump itself is full of  oil so I suspect you are  referring to the plenum, which is part of the induction system and is below the  sump.

  

 The reason that there is some oil in there  is because when the engine is operated at slow speed, such as taxi speed, the  rocker boxes get overfilled with oil, more so on a fresh engine where the ball  sockets of the pushrods have not bedded themselves to each corresponding  rocker.  Then when the engine shuts down the oil in the rocker box  will  run thru the intake guide, down the inlet pipe to the plenum,  assisted by some fuel which, when shutdown, will  " dribble " out of the  fuel nozzle, diluting the oil and lowering is viscosity.  Then the fuel  evaporates leaving the oil residue.

  

 There are 1/8 NPTF holes in the lower  edge of the plenum in which a " sniffle valve " should be installed.   Put a sniffle valve in the lower port when the aircraft is sitting on the  ground.  This valve is used to drain off residual fuel and oil.  It's  primary purpose is to minimize an induction fire during a balked  start.  Use the one made by Airflow Performance which has 1/8 NPTM thread  on one end and -4 flare on the other.  Run a line overboard from underneath  the cowling.

  

 Monty Barrett

 Barrett Precision Engines, Inc.

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