SonexBuilders.net

Hi again,

Saw a 2.1 AV on the weekend on a Sonex airframe. I'm hoping to purchase the aircraft.

I've no experience of VWs, so I'm interested in knowing if oil leaks are common/normal, and if so, where on the engine they typically originate from.

The one I saw could have been leaking from just about anywhere, but I'm pretty certain that it wasn't from the crank at the prop end.

Engine has breather to closed steel bottle on firewall with oil return line to the front of the engine.

Cheers

CC

Most common places for oil leaks:
- valve cover gaskets
- oil sump gaskets
- cam shaft plug
- rear crank seal
- case split surfaces
- prop hub

Oil won't generally leak around the prop hub unless the crankcase is not vented properly. If the breather tube is going to a closed bottle then that could definitely cause the crankcase to be overpressured.

BTW, if a VW engine isn't leaking any oil at all....it's probably out of oil.

I hate the fact that I still have a few minor leaks but i hearken back to my student days in C150's when my instructor told me that " if there is no oil on the bottom of the airplane there probably wasn't any in the engine for the last three students" kinda makes sense but I would rather not have any oil in the cowl or on the bottom of the fuselage.

Thanks for the comments.

Sonex have also answered my email on this subject, and what they have said suggests that the oil leak I have seen is excessive. The essence of their reply was to say that they don't usually have to add oil between scheduled changes.

They also remarked that ALL air-cooled engines will let out some oil. My two Jabs that I have had did not (apart from pumping it into the bottle).

I do prefer Sonex's immediate answers to my questions in preference to the silence that would have come from Bundaberg from a similar enquiry!

Unfortunately, the only way to really tell where an oil leak is coming from is to completely clean off the engine, run it for a bit, and see where the fresh oil is coming from. Eliminating all oil leaks on a VW can be done but it's a nearly impossible task sometimes! Most owners I know are comfortable with tiny amounts of oil seepage as long as there's nothing excessive. On my Waiex, I generally get a little bit of oil from around the sump cover plate that eventually ends at my cowling exit area, but it's nothing I can't comfortably live with.

Remember that the engine will use a little bit of oil in the combustion process, so it's normal to add small amounts of oil from time to time. Even healthy engines require this. Personally, I wouldn't be too concerned if you need to add a little bit every 10 hours or so.

Could you describe how much oil you saw on the Sonex you looked at? It's tough to judge quantity of oil; even a ounce of oil can look like a major leak once it's spread all around the engine compartment! Was there enough to "run" down the bottom of the fuselage?

radfordc wrote:Most common places for oil leaks:
- valve cover gaskets
- oil sump gaskets
- cam shaft plug
- rear crank seal
- case split surfaces
- prop hub

Oil won't generally leak around the prop hub unless the crankcase is not vented properly. If the breather tube is going to a closed bottle then that could definitely cause the crankcase to be overpressured.

To the oil sump gaskets I'll add this: mine was leaking from around the acorn nuts. All of them. I took each nut off one by one (so I didn't have to drain the oil), cleaned off the oil and the mating surfaces (and the copper gasket), added some RTV at the base of each stud, then reinstalled the copper gasket and nuts. So far no more leaks.

Mike Smith

No need to clean off the entire engine to find an oil leak. An old mechanics trick is to dust all the oil on the engine with baby powder. Run the engine for a few minutes and after you shut it off it becomes real easy to trace the oil back through the powder to the source. Once you find and fix the leak then you can go back and clean the engine up.

Keith
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