Date: 16 January 18, 10:59 AM
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 Crankcase breather tube in pitts



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Hi all,

Today I landed my pitts half covered in oil (right side has oil everywhere). The oil seems to originate from the hole I drilled into the crankcase breather tube (
thanks to some interesting info posted by Colondel Sanders: http://www.pittspecials.com/articles/CrankBreather.htm)) and also dripping heavily out of the actual breather tube at the tail. Outside air temperature was around -8 celcius. After about 15 minutes of aerobatics I noticed a weird vibration. I have felt weird vibrations before for no reason, so I thought I would have been imaginging things, after all, something always vibrates. A minute later I smelled something funny. A faint fire smell, but no smoke. Like a campfire smell but not the burning plastic smell. Time to land... Spotted a moose on final (that was nice) and landed. In the circuit the plane behaved normally. After landing I decided to check the cowling. Opened the left side, all looked normal. Walked around to the right side and there was oil on the fuelage, wings, tail. Everywhere. Yikes.

Opened up the cowling and the oil seemed to come out of the hole in the crankcase breather tube (half inch oil covered with electrical tape with a razor blade cut in it). There was no oil leak around the engine or before the engine. Lots of oil on the firewall (right half) Hoping the crankshaft seal is still ok. Called some mechanics and people in the known. The most obvious thing would be that something froze in the breather tube. If that's the case, I don't understand why the breather tube was dripping oil after landing. I did notice some slush at the end of the tube, and a lot of oily slush on the tailwheel assembly.

What I don't understand: IF the breather tube was actually frozen, and the hole I drilled took over, why is there soo much oil leaking? About half a quart I would estimate. On a normal flight, it hardly spits out any oil. Would this cause a vibration somehow?

The burning smell was probably the oil hitting the hot exhaust, as oil was also dripping on there.

Anyway, I'm not flying untill my mechanic takes a look, but since it's my lovely buttock on the line, I'm trying to find out more information...

Regards,
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Linkback: http://scudrunners.com/Forum/maintenance-and-aircraft-resources/26/crankcase-breather-tube-in-pitts/7760/

Colonel Sanders


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Although the mess is scary, it's really no big deal.  Wipe
it up with some mineral spirits and rags.

How much oil you dump out the breather is actually a
function of how well your particular flight empties the
slobber pot, assuming you have a Christen 801.

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Interesting...
It's a christen 803 oil separator which some google fu says me it is part of 801 inverted oil system, so that seems to check out... Thank you!

Does that mean, that if the oil breather tube was not frozen, and there was no whistle valve, the same amount of oil would have come out of the tail? Or does the slobber pot spill out more oil if the pressure builds up and the breather line clogs up?

Colonel Sanders


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Correct!  When the slobber pot isn't drained fast enough - another topic -
the overflow normally goes out the tail.

However, if you have a relief hole / whistle slot opened up, some or all
of that oil will be vented into the engine compartment and will slime the
side of the airplane, Ghostbuster-style.  Although this is scary the first
time it happens, it is really no big deal.  Doesn't hurt the airplane, it
just makes an annoying mess of your shiny toy which is easily wiped up.

I remember a few years back, I made a complete mess of an oil change.
I wiped it up as best I could, but my father (in formation) thought I was 
running the smoke on takeoff as I burned the oil off the exhaust, as it
heated up.

I found it helped to spend some time around radial engines.  You get a
but more tolerant of oil splashing about.

I have no idea what caused your vibration.  Lycomings drive me nuts
with their intermittent rough-running, which would cause me to declare
a mayday if I was behind a Continental that did the same thing.

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Always nice to know that I didn't destroy my engine  ;D

Colonel Sanders


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PS  It's a good idea to pull the slobber pot and
slosh a gallon of mineral spirits around inside it
and make sure the slider is free.

If you haven't already, grab a copy of this PDF:

http://monrv-3.fr/docs/Christen.pdf

It says that 1/2 quart loss in 10 minutes is ok.

That's a hell of a mess if it makes it onto the
side of your airplane.

Slick Goodlin


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That's a hell of a mess if it makes it onto the side of your airplane.
Yeah, especially when it only takes like three tablespoons of oil to coat the belly of a small plane.

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PS  It's a good idea to pull the slobber pot and
slosh a gallon of mineral spirits around inside it
and make sure the slider is free.

If you haven't already, grab a copy of this PDF:

http://monrv-3.fr/docs/Christen.pdf

It says that 1/2 quart loss in 10 minutes is ok.

That's a hell of a mess if it makes it onto the
side of your airplane.

Great file!

If you fly unlimited-class sequences. I hate to say I am nowhere near there :-)
I liked the paragrah below that though, and their procedure to find the "normal oil level". I should have mentioned, but the plane just came out of its annual. We changed the oil from W100 plus to 15W50 and started with 7 quarts of oil on the stick. After the oily flight, the level was 6.5 . Waiting for a flyable day to try again and see if it stabilizes.


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