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Corrosion Protection of your Lycoming or Continental Aircraft Engine

Corrosion causes 2 of the 3 most common reasons engines need major repair before TBO.

  Over the years running an engine shop I came to believe that corrosion is a more expensive problem than most aircraft owners realized.

A steel cylinder has a hone pattern that averages 25-35 micro-inches in height and  once the hone pattern is worn off the barrel – resulting in a polished surface- oil flows past the rings and into the combustion chamber. Even though the dimension of the barrel is essentially the same,  piston rings don't control oil on a polished cylinder barrel. Corrosion causes this polishing wear.

Close-up of newly honed cylinder barrel showing cross-hatch hone pattern.

 Cylinders freshly removed from engines, brought in with oil still in the cylinder  and left over a winter weekend, when wiped with a white tissue paper, will have red rust stains on the paper. Your cylinder barrel is also rusting when it's on the engine and the weather is humid with temperature changes that create condensation. You can't see this microscopic layer of rust since the cylinders are on the engine but it's happening.

The next time you fly your piston rings wipe away the microscopic layer of rust leaving the surface with a little less hone pattern. Over several years the hone pattern disappears, and the barrel becomes polished from the repeated removal of thin film corrosion. Your engine starts burning oil and your cylinders require a expensive repair.

It’s common on engines in service for 10 or more years to have bad camshaft lobes or camshaft followers. The damage starts off with corrosion pits that gradually coalesce into larger pits. It is common for the camshaft follower to fail first and then damage the camshaft lobe. If found early enough it is possible to replace the followers and save the camshaft. I didn’t catch mine early enough and had to replace the camshaft and followers on my C-182.

	Camshaft follower showing corrosion pits (this is the part that rides on the camshaft lobe) Is not detected using oil analysis Leads to spalling pictured below Will destroy the camshaft lobe Camshaft Lobe Inspection
Notice how the black line around the edges wobbles. It is thinner  at the 8:00 o'clock position and wider at the 3 o'clock position. This is caused by the lifter wobbling in the crankcase bore. When you see this you know that the crankcase bore is worn out.

Corrosion pitting of camshaft follower surface.

Camshaft Follower Normal on Left    Badly spalled on Right Spalling:  (Severe damage characterized by large pits, cavities and cracks; related to overload and fatigue) Is not detected using oil analysis until the late stages Is not detected using oil filter analysis unless the filter is examined by rinsing the filter media and using a magnet to separate the fine slivers Has ruined the camshaft lobe Results in engine power loss with no engine roughness May also be caused by a sticking valve.

Normal camshaft follower on left. Notice circular pattern that indicates lifter is rotating as it should. Even dark circle on edge shows lifter was not wobbling in the crankcase bore as might happen if the bore is worn

Badly spalled camshaft follower on the right. The final result of corrosion pitting.

Change the oil in the fall rather than the spring. Fresh, clean oil offers better corrosion protection during the wet weather when you won't be using your airplane as often.  This is more important for engines that use “breathers” as you are recycling some of the waste products back into the engine. Its not only oil that goes out the breather but water and sulfuric acid.

 If your airplane is stored in a tee hanger then make sure that your hanger has  fresh air and ventilation. Hangers trap moisture and on hot winter days become humid enough to condense on the propeller blades and the cylinder walls. Airplanes parked inside are kept dry from the rain but may suffer from humidity and condensation. Those revolving roof-top vents would be nice.

 If your engine is going to be stored then you might consider installing Dehydrator Plugs (part number AN4062-1 or MS27215-2  for the standard 18mm used on Lycoming and Continental engines. AN4064-1 14mm for use on Franklin engines) in the spark plug holes. These plugs have a moisture absorber  and visual indication of moisture. When you purchase them they are bright blue. When they cannot absorb any more moisture they turn pink. Just remove them and take apart and spread the absorbing crystals out on a cloth and dry in the oven and you’ve re-energized them. A good investment! Note: we haven't been able to find a source for 14mm dehydrator plugs at this time

 My first experience with preservative oils was a customer who had an engine “pickled” with preservative oil for about 15 years. The preservative changed to tar and items like hydraulic lifters were completely tarred  together. No corrosion but the engine had to be completely taken apart with some difficulty!  Since then I’ve been more than a little conservative about what I recommended or sold.

The Dehydrator plugs we sell can be taken apart, dried out in an oven set to warm and re-used.

  As the dehydrator absorbs moisture it turns from blue to pink

 During the late 1970’s or early 1980 when the great boom in aircraft sales ended and Cessna stopped production of piston aircraft many brand new airplanes sat unsold for a long time. We got experience repairing rust damage on new engines. The airframe manufacturer said the rust was an engine problem, and the engine manufacturer said their warranty didn’t cover improper storage and preservation. Tuff luck – your new 200,000 airplane with a rusted engine isn’t covered under warranty! About that time we heard about a “flyable” preservative oil. Just what we needed, manufacturer approved, flyable.

 It took another 20 years for  the product to become somewhat available, Shell Fluid 2F. This product could be used for up to 25 hours (sometimes called a ferry oil) which allowed short flights or completely warming up the oil and getting it fully distributed in the engine.

 Don’t get too excited though, Shell discontinued 2F probably for disappointing sales but from our vantage point from bizarrely poor distribution. When Shell discontinued the product I purchased all I could find and continued selling 2F for another year until I ran out.

There is now a replacement, Phillips Multi-Viscosity Anti-Rust Oil. Anti-Rust oil meets the same mil-specs, and comes in the same 1 gallon containers. One unique property of this oil is that it can be run as a break-in oil for up to 10 hours on new engines. If the engine is going to be run on a test-stand after overhaul but not going to be placed into service for awhile this could be a good oil to use on the test stand. 

The best corrosion protection is to fly your airplane every day. The more practical suggestion is to keep clean, fresh oil in the engine. For stored engines use dehydrator plugs in the cylinders and Anti-Rust oil in the engine. 

Phillips Anti-Rust Oil is now available at Sacramento Sky Ranch

Companion article: Crankcase Distillation of Water by Air Oil Separators

For more corrosion information download a demo copy of our Galvanic Corrosion Software for windows

Galvanic Corrosion Potential of Metals. Compares different metal combinations for dissimilar metal corrosion and various protection methods. Version 3 View Screenshot

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 1944

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.