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Engine Storage

By Bill Claxon (originally published in EAA Vintage Airplane, December 1994)

It is generally known that when the aircraft engine is not run for long periods of time the idle time has a detrimental effect on the engine. In fact, long periods of idleness vastly reduces TBO. Cylinder wall corrosion is one of the problems. Teledyne Continental states that the new or newly overhauled engine is extremely prone to this corrosion until it has about 50 hours of running time. Not only do the cylinders corrode, so do the rest of the internal parts. Continental states that the best way to care for and preserve the engine is to fly once a week. Lycoming also goes along with this. However, as winter approaches we tend to leave the airplanes for long periods of time therefore, engine preservation methods may be in order.

Short Term
If the airplane is not used for a month or so, simply pull the prop through six or so times each week and leave the prop 45 degrees to 90 degrees from the original position. Fly the airplane to have the engine reach full operating temperatures to burn out the moisture and contaminates.

DO NOT turn the prop backwards as this runs the oil pump backwards. This pumps the oil out of the oil galleries and results in a longer time for the internal parts to become lubricated on engine start up. Sometimes they are turned backwards to prevent firing if a P-lead is open to allow the engine to fire. Do observe some safety rules and this should not become a problem.

Safety Rules
Verify that the mag switch is "OFF"
Throttle position "CLOSED"
Mixture controlled "IDLE CUTOFF"
Set brakes and chock wheels
Leave aircraft in tiedowns
Have cabin door unlatched
DO NOT stand in propeller arc

You should fly your airplane at least once every 30 days.

Long Term
If you do not fly much in the winter, longer term preservation techniques may be in order. These simple and inexpensive procedures may pay large dividends come Spring.

Start with cylinder preservation. Remove the top spark plugs and spray atomized MIL-46002, Grade 1 preservative oil through the spark plug hole with the cylinder at bottom center . Repeat this for each cylinder. Then stop the crankshaft with no cylinder at top center. Respray each cylinder to thoroughly coat all cylinder surfaces by moving the spray nozzle from top to bottom. The replace the spark plugs.

Continental says to spray two ounces of the preservative oil into the oil filler tube to preserve the interior parts; however, with the kidney oil tanks many use I wonder how much preservative oil will get to the internal parts. With the engines that have the oil filler in the case this seems more plausible.

Seal all engine openings such as the exhaust, breather, carb intake, etc. with suitable plugs, moisture proof tapes, or whatever is applicable. Wads of paper stuffed in the openings can be effective. (Since paper will absorb moisture, you may wish to cover the paper wad with plastic wrap.-HGF) Place red streamers at all places where plugs are installed and on the propeller. You may want to pace a placard on the prop to tell people the engine is preserved and do not turn the propeller.

Bringing out of Storage
When it is time to bring the engine back to life and start a new flying season, remove all the seals and streamers. Take out the bottom plugs and turn the propeller several revolutions to clear out the excess preservative oil. Reinstall the spark plugs and use normal starting procedures. Observe the safety precautions again when turning the prop by hand.

These simple procedures should go a long way to dispel some of the ravages of winter disuse of the airplanes. There are further steps that can be taken to enhance this preservation, especially, those airplanes that will be put away for most of the winter.

From Continental, drain the oil and install MIL-C-6529 Type II oil. Run the engine until normal operating temperatures are reached. Better still, fly the airplane for thirty minutes and allow the engine to cool to room temperature.

Spray the cylinders with the preservative oil as stated earlier. Then, replace the spark plugs with MS27215-2 dehydrator plugs. Be sure the dehydrator plugs are blue. The pink ones are already saturated with moisture and will not absorb the engine's moisture. Protect and support the spark plug leads with AN4060 protectors. Also place a bag of desiccant in each opening prior to sealing as stated earlier. Again, it is a good practice to place streamers on each plugged opening and the propeller and add the sign not to turn the propeller.

To return the aircraft to service, remove all plugs and desiccant bags from all openings. Remove the bottom spark plugs and rotate the propeller several revolutions to remove the excess preservative oil. Remove the dehydrator plugs and install all spark plugs. Ten turn the engine by hand to be positive there is no oil in the cylinders to cause liquid lock. Reinstall the spark plug leads.

Continental says to drain the preservative oil and replace it with the recommended lubricating oil. The next paragraph has a warning:

When returning the aircraft to service, do not use the corrosion preservative oil referenced in paragraph 5-4.a.1 more than 25 hours. (From Continental manuals)

I would take this to mean that the preservative oil is safe to use for this length of time. The advantage of this is that you could take the airplane out of storage without changing the oil. Then to put the engine back into storage, all you need to do is replace the desiccants and respray the cylinders.

As I said, I do not understand the spraying of the preservative into the oil filler neck of the Continental engines to do more than to preserve the oil tank, but the Continental manuals say to do this. I phoned Continental Service technicians and called their attention to this statement in the manuals. They said this was not a correct procedure. The technician said to remove the crankcase breather and to remove the breather fitting that screws into crankcase. Then, use a sprayer that can reach into the crankcase to spray the preservative oil into the top side of the crankcase. They suggested to use a long sprayer that can be rotated to be sure to spray all parts of the upper case. This doesn’t look the easiest to me, but whatever coverage obtained will help.

(Since I knew my engine would be in storage for an extended period, and planned on overhauling the magnetos, I removed the one and sprayed preservative oil past the magneto drive gears into the crankcase. - HGF)

Textron Lycoming
Textron Lycoming Service Letters take a slightly different approach. They say to use one part of concentrated MIL -C-6529C Type I added to three parts MIL-C-6082C (Grade 1100) mineral aircraft engine oil to replace the lubricating oil. Follow the manufacturers instructions when mixing the oils. Operate the engine until operating temperatures are attained. Immediately drain the preservative oil for engine storage. It may be saved for future use. These oils are not for lubrication, only for corrosion prevention. However, the engine does not need to be flushed when the sump is refilled with lubricating oil.

Remove the spark plugs and spray the cylinders with MIL-L-6529C Type I preservative oil. The oil is to be heated to 200 degree Fahrenheit to 220 degree Fahrenheit and sprayed while turning the engine five revolutions with the starter. Then spray each cylinder after the engine has stopped and do not turn the propeller.

Follow the preservative oil with the sealing, desiccants, and dehydrator plugs.

MIL-L46002, Grade 1 Oil is available:

Daubert Chemical Company
4700 South Central Avenue
Chicago, IL

Ashland Oil Inc.
1401 Winchester Avenue
Ashland, KY

MIL-C-6529, Type II may be formulated by mixing one part of preservative oil to four parts of new lubricating oil of the recommended grade. These are: ESSO RUST-BAN 628, or COSMOLINE No. 1223, as well as some of the equivalents.

I was unable to find these preservative oils or the dehydrator plugs listed in any of the many catalogs normally available to the general aviation public. (I buy mine from parts vendors at the larger fly-ins like EAA OSHKOSH or Sun 'n Fun.-HGF) I am contracting Lycoming and Continental to find the sources for these products. As for the moisture proof tapes, the building and department stores now have waterproof duct tape which should work well for sealing the openings. Lycoming lists the dehydrator plugs as Avco P/N 40238. When the desiccants and dehydrator plugs are saturated with moisture, they can be rejuvenated by warming them until the color is once again blue. This removes the moisture they have absorbed.

The engine manufacturers recommend these preservative measures, so if we do these things we may save the engines from the ravages of winter or other storage. It would be a good idea to preserve the engine when the airplane is down for extensive rebuild or repairs. In as much as both makes of engines require essentially the same corrosion prevention, it would seem that either system would work for either make of engine. Use your preference.

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