FAA Powerplant Written Practice Test

When depreserving an opposed cylinder engine, what should be done if small amounts of corrosion prevention compound remain on the cylinder walls?

1. Wipe them clean with a cloth

2. Allow them to dry naturally

3. Remove all residue immediately

4. Nothing, small quantities are acceptable

The correct answer is: Nothing, small quantities are acceptable

When depreserving an opposed cylinder engine, it is generally acceptable to leave small amounts of corrosion prevention compound on the cylinder walls. This is because these compounds are specifically designed to prevent corrosion, and a small residue can continue to serve that protective function. In aviation maintenance, it is understood that complete removal of all substances isn't always necessary, especially if they do not impede functionality or create an obstruction. Typically, if residues are extensive or if they interfere with engine operation, they should be removed. However, minor amounts help ensure that the interior of the engine will remain protected from moisture and other corrosive elements during normal operation. Thus, recognizing that small quantities of these compounds are acceptable reflects a practical approach to engine maintenance, where the protective qualities of the residual substance can be utilized rather than posing a risk to engine performance.