Venting of Lycoming 0-290 D Engine

On Apr 27, 11:22 pm, "Morgans" wrote:
wrote



Unless that engine is really tight (pretty much zero ring
leakage) he'll end up with backpressure in the crankcase and will blow
the front crank seal out, losing oil at a good clip

I agree.

How come airplane engines don't have PCV valves, plumbed back into the intake
manifold, like cars? You could even use an oil separator, before the gas enters
the manifold, if too much oil was worried to be a problem.

An arrangement like that would solve the oily discharge on the belly, I would
think.

Might even keep the intake valves lubricated a little bit! g

I wonder what the answer is, and why that solution would be a problem. I'm sure
it has been tried, since it seems there is truly nothing new under the sun, when
it comes to airplanes.
--
Jim in NC

No PCV because the aircraft engine runs at high manifold
pressures most of the time, so there's too little differential (read
"manifold vacuum" to suck a PCV valve open and adequately purge the
gases. On an auto, when the throttle is fairly open, the PCV valve
pretty much closes. The valve has to be there to stop flashback in
case the engine backfires; the flame would ignite the gases in the
crankcase. Boom, big ugly mess and a major CG shift. In the auto, the
gases will, at full throttle or nearly so, back up through the
crankcase intake filter and into the air cleaner and get cleaned up
that way. The filters act as flame arrestors. When the engine gets
old, there's too much blowby and lots of it exits this way, and its
moisture freezes up the crankcase intake filter in colder weather.
BTDT.
It could be done, with some different plumbing, which adds
weight, expense, and certification hassles. When the EPA or whoever
decides that airplanes need all the antipollution stuff that cars
have, we'll see it on airplanes and our useful loads will drop
considerably.

Dan

"Morgans" wrote in message
...

How come airplane engines don't have PCV valves, plumbed back into the
intake manifold, like cars? You could even use an oil separator, before
the gas enters the manifold, if too much oil was worried to be a problem.

Jim ...........

If you've ever seen the oil that collects in an oil/water separator, you
wouldn't want it back in an engine. I realize that some of the water in the
separator is condensation from the air coming back up the vent from the
outside after shutdown, but even so, the watery sludge in the reservoir is
really gross. Best to spend a few bucks and a couple of hours building a
simple firewall-mounted separator (plans available in old issues of Sport
Aviation when they had such things).

Wiping the bottom of a fuselage is kind of a Zen thing for me. Takes me back
to a simpler time.

Rich S.

"Morgans" wrote in message
...

wrote

Unless that engine is really tight (pretty much zero ring
leakage) he'll end up with backpressure in the crankcase and will blow
the front crank seal out, losing oil at a good clip

I agree.

How come airplane engines don't have PCV valves, plumbed back into the
intake manifold, like cars? You could even use an oil separator, before
the gas enters the manifold, if too much oil was worried to be a problem.

An arrangement like that would solve the oily discharge on the belly, I
would think.

Might even keep the intake valves lubricated a little bit! g

I wonder what the answer is, and why that solution would be a problem.
I'm sure it has been tried, since it seems there is truly nothing new
under the sun, when it comes to airplanes.


A) They don't have to.

B) PCV as found on automobiles won't work well at higher loads (no vacuum),
but new sytems for large diesel trucks are now coming onto the market to
meet emission standards - they have the same lack of vacuum...

--
Geoff
The Sea Hawk at Wow Way d0t Com
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