National Aeronca Association Bulletin Board

I had a strange thing happen today, just after I took off from my pasture I noticed some small puffs of smoke under the panel.

Needless to say I returned to the ground post haste. Careful inspection showed nothing abnormal in the engine area so I took off again. I flew about ten minutes and it happened again. I flew around for ten or fifteen more minutes and it appeared to still be happening but didn't seem to increase.

The smoke was very hard to see because of the bright sun and darkness underneath the pane. It may have been only reflection in my glasses, but it got my attention. There was no strong odor of oil burning.

My oil level was about a quart low and the temp was about 195*F. Outside temp was 83*F.

My best guess is oil dripping on the exhaust somewhere but I could see nothing. Tomorrow, out comes the inspection mirror and bright light!

Had the same thing happen to me, C85-12, the oil filer cap came loose and oil was splashing onto the muffler. It only takes a few drops to make lots of smoke. I didn't spot the smoke, my passenger did. You had to turn a certain way in the sun to see it.

Bob

Bob,

I found it today, it was oil dripping onto the heater shroud directly under a push rod tube connection.

I hadn't flown in about three weeks so I guess the oil had accumulated a bit and burned off right after climbing out at full power.

Next time I'll make sure to wipe it down first. Stopping those push rod leaks is just about impossible.

Gus,

Only sure cure I have found is the new style pushrod setup for curing leaks.

Joe A

If you have a beading tool for the pushrod tubes, you can re-bead them with a drop of green lock tite between the tube and cylinder head. I bought the REAL gasket tubes and swear by them

Jody,

Are you talking about the upgraded pushrod tubes that require an STC?

OK Joe and Jody, what are these new mystery, magic push rod tubes the rest of us don't know about??

Gus,
They are the O470 style pushrod tubes. Continental offers them on the new cylinders for an extra hundred bucks each. I believe Real Gaskets started them via an STC. http://www.realgaskets.com/images/bwcolorpush.gif
Paul

Paul,

Thanks

I flew it another hour today with the smoke coming in all the time. Not much, but some.

There was a lot more oil on the cowl bottom than has ever been there before so this requires a much closer look. At least now there is enough oil so that it is easier to trace.

This makes me think I have more of a problem than just pushrod tubes.

Gus,
I would pull the cowl for a look. Clean it up real good and run it up with someone holding a rag over the breather it will cause the leak to show up very quickly. Be careful there is a killin' stick up front.
Paul

Gus,

I had oil dripping from the push rod tube clamps on the front two cylinders for the last 40 - 50 hours and getting on the muffler shroud. I recently had the nose bowl off when I changed the propeller and noticed a dust line atracted by oil coming from a cover on the front right side of the engine(sitting inside the plane) that looks like where a fuel pump would bolt on. My mechanic pulled the cover and made a new gasket. That has so far stopped the oil from dripping off the clamps. For what its worth

Pulling the bottom cowling is my next move but will have to wait until our return from the NW.

The puffs of smoke also make me suspect they could be coming from the crankcase breather.

There is enough oil running across the belly now so that I don't think the leak will be hard to find. It wasn't doing this six hours ago?

Push rod tube leaks have always puzzled me because that oil is not under pressure, it is just gravity draining returning oil??

I pulled the bottom cowl and found no leaks of any kind, there were a few old drops of burned oil on the heater muff but not enough to make all the smoke I've been seeing.

I flew it another two hours XC Sun and had the same thing happen. I finally decide, while contemplating a forced landing at any moment, that it really is the vent tube, but can't see how all that smoke could come into the cabin.

My next move is to reinspect for oil leaks and then experiment with different lengths of vent tubing.