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Message
I wrote the group asking
for help in diagnosing a puzzling intermittent oil loss problem. Steve
Colwell responded with a note (below) and suggestions on how to test by
measuring crank case pressure during a test flight.
We replicated his tests
and his results finding little blow by under ground and flight
conditions (less than an inch of water pressure crank case pressure) until I
slowly pulled the throttle for descent from 6500 feet. As the manifold
pressure dropped below 18-19 inches we had indications of huge increases in blow
by and ultimately had some oil came up the nylaflow tubing we had stuffed in the
breather and connected to an airspeed indicator in the cabin. I put out
speed brakes, gear, and flaps and brought it home with 20+ inches of
manifold pressure in the descent to minimize the oil mess. Removing
the cowl, we found oil splattered as before.
It is ring flutter arising
from piston problems. Steve had his problem at 40 hours, and I have
47. I have contacted Performance Engines (engine builder) and ECI
(cylinders) and will pull jugs tomorrow. We shall see.
Grrrrr.....
Fred
Moreno
You
may have the same problem I had. I was blowing a lot of oil out the
crankcase breather too. My Performance Engines IO-550 had forged and
coated pistons that expand at a different rate than the stock Continental or ECI
cast pistons with a steel band for the compression ring land. The
compression rings had worn so much in the lands on all 6 pistons they would
“flutter” when power was reduced. The engine had about 40 hours TT.
To test the pressure in the crankcase breather, tap a manometer into the
breather about ½ it’s length or closer to the engine. My engine would show
zero pressure on the ground regardless of power setting. On the takeoff
roll still zero. At about 120 knots it would jump to 5” and stay there
until power was reduced. When MP was slowly reduced to about 18” the
pressure in the crankcase vent line climbed to over 30”. That was when all
the oil was being blown out the breather. The prop was unloaded just
enough to allow the worn rings to flutter up and down in the ring lands and
allow combustion pressure into the crankcase.
A
mechanic and I spent weeks chasing this problem with ideas from many
sources. The good folks at ECI (Engine Components Inc. of San Antonio, mfg
of the cylinders) had it figured out as soon as they heard the symptoms.
ECI honed my cylinders and gave me new cast and steel banded pistons with rings
at no charge and within 48 hours. We got the cylinders back on just in
time to fly to Oshkosh. The belly is clean and my catch tank for the
Andair Air-Oil Separator is bone dry.
Steve
Colwell Legacy N15SC
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