Cleaning the powerplant is an important job and should be done thoroughly. Grease and dirt accumulations on an air-cooled engine provide an effective insulation against the cooling effect of air flowing over it. Such an accumulation can also cover up cracks or other defects.
When cleaning an engine, open or remove the cowling as much as possible. Beginning with the top, wash down the engine and accessories with a fine spray of kerosene or solvent. A bristle brush may be used to help clean some of the surfaces.
Fresh water and soap and approved cleaning solvents may be used for cleaning propeller and rotor blades. Except in the process of etching, caustic material should not be used on a propeller. Scrapers, power buffers, steel brushes, or any tool or substances that will mar or scratch the surface should not be used on propeller blades, except as recommended for etching and repair.
Water spray, rain, or other airborne abrasive material strikes a whirling propeller blade with such force that small pits are formed in the blade’s leading edge. If preventive measures are not taken, corrosion causes these pits to rapidly grow larger. The pits may become so large that it is necessary to file the blade’s leading edge until it is smooth.
Steel propeller blades have more resistance to abrasion and corrosion than aluminum alloy blades. Steel blades, if rubbed down with oil after each flight, retain a smooth surface for a long time.
Examine the propellers regularly because cracks in steel or aluminum alloy blades can become filled with oil, which tends to oxidize. This can readily be seen when the blade is inspected. Keeping the surface wiped with oil serves as a safety feature by helping to make cracks more obvious.
Propeller hubs must be inspected regularly for cracks and other defects. Unless the hubs are kept clean, defects may not be found. Clean steel hubs with soap and fresh water, or with an approved cleaning solvent. These cleaning solvents may be applied by cloths or brushes. Avoid tools and abrasives that scratch or otherwise damage the plating.
In special cases in which a high polish is desired, the use of a good grade of metal polish is recommended. Upon completion of the polishing, all traces of polish must be removed immediately, the blades cleaned, and then coated with clean engine oil. All cleaning substances must be removed immediately after completion of the cleaning of any propeller part. Soap in any form can be removed by rinsing repeatedly with fresh water. After rinsing, all surfaces should be dried and coated with clean engine oil. After cleaning the powerplant, all control arms, bellcranks, and moving parts should be lubricated according to instructions in the applicable maintenance manual.
In general, solvent cleaners used in aircraft cleaning should have a flashpoint of not less than 105 °F, if explosion proofing of equipment and other special precautions are to be avoided. Chlorinated solvents of all types meet the nonflammable requirements but are toxic, and safety precautions must be observed in their use. Use of carbon tetrachloride should be avoided. The Material Safety Data Sheet (MSDS) for each solvent should be consulted for handling and safety information.
AMT’s should review the Material Safety Data Sheet (MSDS) available for any chemical, solvent or other materials they may come in contact with during the course of their maintenance activities. In particular, solvents and cleaning liquids, even those considered “environmentally friendly" can have varied detrimental effects on the skin, internal organs and/or nervous system. Active solvents such as methyl ethyl ketone (MEK) and acetone can be harmful or fatal if swallowed, and can be harmful when inhaled or absorbed through the skin in sufficient quantities.
Particular attention should be paid to recommended protective measures including gloves, respirators and face shields. A regular review of the MSDS will keep the AMT updated on any revisions that may be made by chemical manufacturers or government authorities.
Dry Cleaning Solvent
Stoddard solvent is the most common petroleum base solvent used in aircraft cleaning. Its flashpoint is slightly above 105 °F and can be used to remove grease, oils, or light soils. Dry cleaning solvent is preferable to kerosene for all cleaning purposes, but like kerosene, it leaves a slight residue upon evaporation, which may interfere with the application of some final paint films.
Aliphatic and Aromatic Naphtha
Aliphatic naphtha is recommended for wipe down of cleaned surfaces just before painting. This material can also be used for cleaning acrylics and rubber. It flashes at approximately 80 °F and must be used with care.
Aromatic naphtha should not be confused with the aliphatic material. It is toxic and attacks acrylics and rubber products, and must be used with adequate controls.
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