Oil analysis - corrosion detection

[N601RX]

A friend had his warrior overhauled, flew it once twice a week about 100 hours per year. 5th year his cam/ lifters went south, he had to do another overhaul.

Another friend has many airplanes and one of them he has owned since new a 69 180, about 900 hours never overhauled flys on average once month about 20-25 hours a year and never a problem.

Both airplanes based in IL, the warrior in a cold drafty hanger and the 180 always in a large heated hangar. I wonder if storage also has something to do with it................

I think the heated hanger had a lot to do with it.

[aviatoreb]

I think the heated hanger had a lot to do with it.

 

What does heat have to do with corrosion?  Was the humidity and so forth also controlled in the heated hangar?

[carusoam]

EB,

Most often, moisture content of the air outside is below the condensation point of water(= or <100% RH).

Heating the air, even slightly, drives the RH down very nicely.

This would be a pretty complex discussion of free water molecules being available with oxygen molecules in the presence of the metal.

Suffice it to say, heating the hangar will depress the RH, as well as the overall humidity (if it matters) enough, to keep things from rusting. So, the RH isn't controlled by heating, it's just lowered (all good)

A similar challenge occurs using compressed air, same as breathing O2, dried by compressing and then extra dried by expanding again)

Best I can do to explain why things rust when water is available and why they don't! by removing the water,

How did I do?

-a-

[N601RX]

My shop is totally enclosed. Part is heated, part is not. If a piece of metal or tool is left out in the Unheated part it will start rusting very quickly. Next day sometimes. In the heated part it will takes months before it even starts to get a trace of rust.

[jetdriven]

If you can't fly it at a minimum of every 5 days, I think there is plenty of evidence an engine drier made of an aquarium pump, silica dehydrator beads, and plumbed into the oil filler tube and the breather hose goes a long way to prevent corrosion, almost to the point of not needing to fly it often at all. It keeps the engine dry inside, and no moisture, no corrosion.  Don Muncy has this setup. When we move to a hangar in Feb, I plan to build one as well.

 

This Lycoming lifter corrosion thing is a major epidemic and its shocking how many of these engines have corrosion and get taken out by lifter and cam spalling. I'd guess 3/4 of the engines out there have some form of lifter pitting and it goes a while sometimes, then the destruction mode is terrifyingly quick. In our case everything was normal, the oil filter was "like new" and then bang, over the course of 25-50 hours it was making metal like that picture I just sent in. 3 lifters were shot but the cam actually looked pretty good, except the nose of the two affected lobes were very rough and torn up.  Scott's failure mode was much more slow. In his case the lobe of the camshaft wore down to the base circle.  Pretty much every Lycoming engine torn down shows signs of cam and lifter failure, usually pitting on the lifters. These boards are full of the tales.

[carusoam]

Did I say, I really like how MS works...

Best regards,

-a-

[FlyDave]

I finally got an oil sample from the Bravo off to Blackstone and got the report back last week.

Very interesting comment on the state of the engine.

 

 

[Piloto]

Dave

 

I think you are over concern about corrosion. On an engine corrosion first show on the outside like on the cylinder fins. If the fins looks clean I would not worry about corrosion on the inside. At 1500hrs I would be more concern about cracks on the cylinders, exhaust and other parts. Also check oil pressure at idle with a warm engine. This will give you an indication of bearings wear. It is normal for pressure to drop as engine wear. Also check bottom spark plugs for oil residue. If oil drips out it is time for an overhaul. Exhaust stain color on the belly is also a good indication of engine condition. A white yellowish color is a good indication while a dark brown or black is an indication of burning oil.

 

José