WHAT THE MAKERS SAY
Lycoming’s Operator’s Manual states: ‘Corrosion can occur… on cylinder walls of engines that will be inoperative for periods as brief as two days’ and warns that ground-running a little-used engine ‘will tend to aggravate rather than minimise this corrosion condition.’ It also says: ‘If an engine… does not accumulate fifty [flying] hours within four months, the oil should be changed at four month intervals.’ Their corrosion-prevention process involves spraying a special inhibiting oil into each cylinder through the spark plug holes.
Continental says: ‘The most detrimental effects of engine inactivity are rust and corrosion damage… Lubricating oil… will eventually drain to the lowest point… and is subject to evaporation. The crankcase and cylinders ‘breathe’ in moisture as the air temperature and pressure rise and fall… through the intake and exhaust and through the crankcase breather. Moisture, acids and corrosive lead salts also form inside your engine during start up and again on shut down because of these temperature changes.’
Continental continues: ‘The simplest and most economical solutions are to fly the airplane frequently and change the oil regularly. If you really want to do right by your engine, avoid leaving it stand idle for more than seven days regardless of where it is based.’
This is clearly common to every piston engine, so applies to all Volkswagen derivatives, Jabirus, Rotaxes, Ulpowers and the others, and equally to helicopters and airships. Even some sailplanes and gliders have ‘turbo’ or ‘sustainer’ engines.