Bill,
Thanks
for the ideas, I have been doing some further
testing……………..
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of Bill
Wade
I run an IO-550-B. The installation is FWF from an A-36 Bonanza and though I
didn't do the installation everything was reused that could be. The vent
tubing is aluminum with only short hose sections for
coupling. It runs upward from the filler tube, over the oil cooler and
through the baffling before it turns down and wanders over to the cowl flap.
It appears to be above the filler cap at the highest point. Someone could
check me on this but I'd guess that was the arrangement used by Beech,
possibly to counter a problem like yours. The engine has 2K total time, about
400 hrs since top overhaul, [oil] pressure is
60#. I use 9 quarts (12 qt capacity) and apart from a slight mist
off the front seal it stays squeaky clean. Almost nothing comes out the
vent tube. If you have a
Legacy, can you give me a measurement of the exit end of your crankcase
breather? The easiest reference could be the lower left motor mount hole
in the firewall. How much higher? How far to the right?
I have the IO-550 in a Navion- I'm building a IV-P. I can't
help you with the routing in a Legacy but I thought the way my installation
was done might give you some ideas.
From your
picture that doesn't seem to be an option but would it be possible to gain
height by going over the #2 intake or upward aft of the baffle so that
any oil might separate and drain back to the filler? I
have not tried to get the vent tube higher since the exit from the dipstick
housing is fairly high and the top of the cowl would not allow me to get more
than ½” or so higher.
I figured there wouldn't be much room
inside the cowling but again, based on what I see on my plane, it might be
worth trying.
Does the bit
of aluminum tape in the upper photo cover a previous routing hole? The tape covers a
“Anti-siphon hole” I added after the problem began at the suggestion of ECI
the cylinder manufacturer. It was taped off in the photo for a test and
has been tried open and closed in several tests.
In the upper photo it looks like there's a hole in the
baffle that's been covered over with aluminum tape- it looked to be about the
right size for a vent line.
I had also
been thinking that you might have excessive pressure inside your lower
cowling. I'm trying to explain the manometer change at 120KT-
perhaps the outlet size is adequate up to that point but not enough
to allow increased flow at higher speeds. Since your vent tube terminates
inside the cowling that might pressurize the crankcase. I wouldn't
expect it to cause oil to blow out the breather though- it might come from
somewhere else if that was the case.
I
finally have a glimmer of hope. I relocated the crankcase vent exit
about 2” above the original location and 3/4” further from the centerline of
the cowl exit. In a quick trip around the pattern the belly had only a
thin film of oil rather than a thick coat. The suggestion from a friend
(who managed the service dept. for the Cessna dealer in Sacramento) was to
move the vent exit away from the low pressure area caused by venturi effect at
the cowl exit. I measured the pressure difference between the original
location and the most recent one with a 2” increase on the
manometer.
Interesting- my vent terminates right at the cowl
flap. So it could've been actively sucking oil out of the
engine?
You have
checked for leakage extensively although initially you were wondering
whether there might be leakge from the alternator etc. From that I guess
you had oil all over the rear of the engine?
I notice the vent tube ends quite a bit above the bottom of the
firewall. Air currents inside the cowling can spread oil from even a small
leak all over the place and there's a long way for the vent oil to exit.
Early
on, I washed the engine down with solvent to check the source of the leak, it
is all coming from the breather.
I'd suggest a
temporay extension outside the cowling to see what that might do. The whistle
hole should also be closed off. At the very least that'd eliminate lower
cowling pressure as a factor and any flow from the vent would go straight onto
the belly so you'd have a chance to see if there was leakage from anywhere
else. Also, if there's any way to have oil drain back into the filler it
might help a lot. I removed a Andair
Air/Oil Separator for testing to keep it from masking the results. The
plan is to put it back in the system to minimize oil loss when I am sure what
is going on.
How much
time on the engine and who built It?
It is a Performance
Engine with about 50 hours, stock 9:1 compression and magnetos, Ron Monson has
been very helpful.
My best
guesses- Bill Wade
Mine too-Steve
Colwell
Good luck, hope you get it straightened out.
-Bill
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