REFLECTOR: Blow by

[Scott Derrick]

I know some say that if you puke the top 1-2 quarts out you have excess 
blowby caused by worn rings.

I dispute that because I have been flying two 210's, one is on its 3rd 
new engine and the other its 1st new engine since I have been flying 
them. Three have been Continental reman's, one a widely used engine 
re-builder.  All of them had New cylinder assemblies.

All 4 newly manufactured engines blew the top 1-2 quarts of oil out much 
much faster than after the oil level got down to 8 quarts.  We never 
fill to 10 as pilots. The mechanic that maintains them always would fill 
to 10 during an oil change, but he also said he did that for liability 
reasons knowing the top two quarts would go overboard in the first 5 
hours.  He was perfectly fine with us adding oil at 7-6 full quarts and 
only adding to 8-9 quarts full.

The newly rebuilt 520 in my Velocity, same engine that the 210's have, 
did the same thing.

The minimum oil level in all Continentals in 2 quarts, I think Lycomings 
are the same.

Maximum crankcase pressure is 4 PSI. I've never measured mine, but I do 
know that if you restrict the breather tube too much your case will leak!

I have always wondered if the rear mounting of these engines increased 
the loss of oil in blow by.  My breather outlet is right near the prop 
end of the engine.  In a pusher in climb and slow flight that end of the 
engine is lower than the rest and the oil would naturally be deeper and 
splashing more from the crank. In a tractor that end would be higher in 
climb and slow flight and thus have less oil and splash less?  I don't 
know if there is a connection there. I do know if I run my engine, fixed 
pitch, at a higher continuous RPM I will blow more oil overboard.

Scott