Both manufacturers Lycoming and Continental agree that inactivity in excess of 30 days strongly suggests the need for some special preservation methods and chemicals, especially if the aircraft is located near salt water or similar humid environment.
Lycoming Service Letter SL180 Engine Preservation for Active and Stored Aircraft Lycoming's procedure is as follows:
Install a preservative by one of the following methods:
Drain the lubricating oil from the sump or system and replace with a preservative oil mixture. This preservation mixture consists of one part by volume MIL-C-6529C Type I concentrated preservative compound added to three parts by volume of MIL-L-6082C (SAE J1966), Grade 1100, mineral aircraft engine oil or oil conforming to MIL-C-6529C Type II. Follow carefully the manufacturer's instructions before use.
An alternative method is the use of Cortec VC1-326 preservative concentrate added to the original oil at a ratio of 1 part VC1-326 to 10 parts of oil.
Operate the engine until normal temperatures are obtained. Do not stop engine until oil temperature has reached 180°F. If weather conditions are below freezing, oil temperature should reach at least 165°F before shut down.
Remove sufficient cowling to gain access to the top spark plugs and remove them.
Through the spark plug hole, spray the interior of each cylinder with approximately two ounces of the pre-servative oil mixture using an airless spray gun (Spraying Systems Co., Gunjet Model 24A-8395 or equivalent). In the event an airless spray gun is not available, a moisture trap may be installed in the air line of a conventional spray gun.
Reinstall spark plugs and do not turn crankshaft after cylinders have been sprayed. Note: Oils of the type mentioned are to be used in Lycoming aircraft engines for preservation only and not for lubrication. See the latest revision of Textron Lycoming Service Instruction No. 1014 for recommended lubricating oil choices.
If the aircraft is stored in a region of high humidity, or near a seacoast, it is better to use dehydrator plugs instead of merely replacing the spark plugs as directed in the preceding step. Cylinder dehydrator plugs, MS-27215-2 or equivalent may be used.
Preferably before the engine has cooled, install small bags of desiccant in exhaust and intake ports and seal with moisture impervious material and pressure sensitive tape. Any other opening from the engine to the atmosphere, such as the breather, and any pad from which an accessory is removed, should likewise be sealed. (Desiccant may be obtained through a Textron Lycoming distributor, or aviation catalog or Internet in different quantities.)
Firmly attach red cloth streamers to any desiccant bags installed in the intake and exhaust passages to insure material is removed when the engine is made ready for flight. Streamers should be visible from outside the aircraft. The propeller should be tagged,
"Engine preserved—do not turn the propeller."
At 15-day maximum intervals, a periodic check should be made of the cylinder dehydrator plugs and desic-cant. When the color of the desiccant has turned from blue to pink the preservation procedure must be repeated.
To return the aircraft to service, remove seals, tape, and desiccant bags. Use a solvent to remove tape residue. Remove spark plugs or dehydrator plugs.
With the magnetos off rotate the propeller by hand through sufficient rotation to remove excess preservative oil from the cylinders. Drain the remaining preservative from the engine through the sump.
Engine Preservation Record
Qualty,Safety and Training