Blocked breather tube causing oil leak at prop hub

[sonex1374]

I was recently speaking with a Sonex owner regarding a problem his AeroVee had developed recently where oil was leaking past the oil slinger and exiting the case by the prop hub. This has happened to several other AeroVee owners I know as well. In each case the problem has been a build up of excessive crank case pressure because the engine breather vent was not breathing properly. In this most recent case the breather tube was clogged with sticky goo (a mixture of oil, water and combustion byproducts that had congealed). Cleaning the breather tube solved the oil leak problem.

In some more extreme cases the engine required a larger breather vent tube, or even the addition of valve cover breather vents to be installed before the oil leak stopped. Something to think about if you have a similar problem.

One final thing was also not quite right about that installation was the placement of the air-oil separator. If using a separator, it's essential to place the unit in such a position that it runs hot enough to prevent large-scale condensation of water vapor inside the separator. This can be quite difficult to accomplish sometimes, and for that reason I'm not a big fan of separators on AeroVee's. Some engines will really need separators (Turbos, lots of aerobatics, documented history of pumping lots of oil out the breather), but on a normal-use engine, having a too-cool separator is worse than having no separator at all. In other words, if you're going to use one, you better do it right or not at all.

An alternative to using a separator is to simply use a catch bottle to accumulate and store the oil before it deposits itself onto the belly of the plane. This can be as fancy as you like, or as simple as an empty coke can safety wired to the outlet of the breather vent.

Jeff

[frkatck@yahoo.com]

After I bought my Sonex 4 years ago I noticed some oil seeping out by the oil slinger through the prop hub and one day at 2500 ft the crankshaft broke at the Oil slinger and the prop and all went whirling through the air. (Never found it) I Landed on a road with no damage and trailed it 30 miles home. Went home and changed my underwear. The hardest thing I had to do that day was tell my wife. The new engine included the forceone crankshaft and bearing. I reused the AeroVee accessories
Frank

[Rynoth]

I was recently speaking with a Sonex owner regarding a problem his AeroVee had developed recently where oil was leaking past the oil slinger and exiting the case by the prop hub.

How did the leak show itself?

I've been battling (and I believe finally won) an oil leak at my oil pressure tap, but upon inspection after each flight I was never 100% sure if it was an oil slinger leak or a leak at the tap. Basically I'd have oil on the copilot-side baffle and a little bit of oil on the same side above the cowling air intake and a tiny stream of oil along the top of the cowling. Since then I believe I've solved the leak and the presence of oil in that area is minimal now. What does an oil slinger leak look like?

[mike.smith]

I've had 100% success with my oil separator. Never a hint of sludge, frothy oil or water, and no blockages:
http://www.mykitlog.com/users/display_l ... 492&row=94

The hose "out" of the separator goes to a catch-can that is vented, so if any oil gets past the separator it doesn't get out to the belly. Usually during my annual condition inspection there is nothing in it. That's the only time I ever check it.

[sonex1374]

How did the leak show itself?

Ryan,

The two examples that I've seen with this problem had oil pooled around the oil pump cover, and then the oil dripped or was blown down around the front of the engine case. It didn't initially look like it had come out the prop hub area, but I believe that's just because that area that doesn't collect oil very well. In one of the examples a small line of oil had deposited itself along the outside top of the cowling as well.

This wouldn't be my go-to thought if an engine was leaking oil, but checking the breather is a good trouble shooting step early on.


Mike,

I like the separator you built. It's also nice and close to the engine, which undoubtedly helps optimize things.

Jeff

[fastj22]

I have a friend who put an oil breather suction device on his RV7 with an O390. It was welded to the exhaust and created a suction on the case to pull the vapor. Supposably it increases performance by lowering case pressure and dumps the vapor into the exhaust to be burned off. His worked swimmingly until it coked up and closed shut. Increased pressure blew the prop oil seal off the constant speed prop. He was flying over tiger country and immediately turned to the nearest airport, about 30 miles out. When he landed he couldn't see through the windscreen but was able to taxi off the runway before the engine seized. If I recall correctly, it was not rebuildable. Cost him $50k to put a new motor on it.