REFLECTOR: Oil Breather Nipple Into Exhaust Pipe

[Bob Jackson]

Does anyone have experience or ideas for the best way to weld a nipple into
the exhaust pipe for the oil breather hose?

We want to weld a nipple for our oil breather hose into the short exhaust
outlet pipe of one of the turbochargers (we've custom-added to our IO-550N).
We are aware of several issues and concerns.  One issue is how far the
nipple is extended and/or is angled into the exhaust gas stream.  If for
example on the inside of the pipe, the nipple is extended and angled away
from the turbocharger, it might create a small Venturi effect and help draw
moisture and oil 'fumes' out of the crankcase.  But if angled away too much,
this Venturi might be strong enough to excessively de-pressurize the
crankcase and cause problems.

Or, if the nipple were angled a little too much back into the direction of
the turbo exhaust, it could positively pressurize the crankcase and cause
engine seal problems.

Hopefully, there is an angle of the nipple that creates no positive
crankcase pressure, and with just the proper, small amount of negative
pressure to help draw out the oil fumes slightly.

Another issue we're concerned about is that this short stub of a breather
nipple on the inside of the turbo exhaust pipe could eventually burn through
or break off and strike the prop.  This has apparently happened in the past
with some certified aircraft (not bang into the prop, just break off).

Finally, we've also heard that if the nipple enters the exhaust pipe at
right angles and is flush cut with the wall of the exhaust pipe, not
extending into the inside of the breather nipple, it may be slightly
pressurized and can become completely clogged with 'soot' over a period of
time.

If anyone has experience or suggestions for how far in to extend the oil
breather nipple into the exhaust pipe, and which way to angle it, we would
appreciate the help.

Or alternatively, if someone has a (TCM or Lycoming) engine with a factory
installed oil breather nipple, maybe they could look to see how far the
nipple extends into the exhaust pipe, and at what angle.

Thanks,
Bob Jackson
N2XF -- Ten years and still working!