My Cont. IO-550 (normally aspirated, stock comp ratio)  is blowing enough
oil from the crankcase breather to put a thick coat on  ½ of the belly,
halfway to the tail in 10 min. of flying.  Originally I thought I had
overfilled the 8 qt. crankcase so I drained the oil, changed the filter and
refilled with 6.5 qts.  During runup and takeoff roll the manometer (tapped
into the crankcase vent about the mid-point of its length) will read zero
until plane has about 120 knots indicated airspeed.  At 120 to 200 knots the
manometer reads 4" to 5" with a short spike up to 14" to 20" when power is
reduced in the pattern.  The following tests have been run:



Compression test:  high 60's to low 70's which I am told is normal for
Continentals, oil is normal color (not black, which would indicate blow-by)



Washed engine with mineral spirits to see if any fresh oil was appearing.



Upper plugs are normal color, maybe a dark tan insulator, no fouling
problems



Low pressure on crankcase with 12" balloon on crankcase vent:  takes about 3
min to deflate, tried soap suds around all accessible seals, dipstick cap,
mags, pushrod tubes, etc..



Relocated crankcase vent to right side cowl outlet



Cut a anti-siphon hole 6" above the end of the vent tube on normal left side
exit.



Taped the dipstick cap with aluminum tape.



Put 20 psi air pressure on crankcase, soap suds again, air going past piston
rings, tried turning prop with no noticeable difference from cyl to cyl.



Replaced crankshaft seal.



Anything that required a flight test would deposit the same thick coat of
oil on the belly in a single trip around the pattern.   I have just about
run out of ideas, the engine builder has never heard of anything like this
and the cylinder supplier could only suggest it could be the crankshaft
seal.   It could be a leaking seal in the alternators or mags or ????    I
need help.



Steve Colwell  Legacy   916 505-6099