Aircraft engine piston failure, Rotax two stroke aircraft engine piston failure

Diagnosing Rotax 2 Stroke Aircraft Engine Piston Failure

These two pistons are NORMAL in appearance.

The deposits on the piston dome are from the oil and ash, fuel contaminants and unburned carbon. As the thickness increases with operating time, the colour gets brighter because of higher surface temperatures.

Depending on gasoline and oil used, normal deposits may also be brown, from light tan colour to almost black dark brown.

Heavy black deposits on the piston dome are unburned carbon accumulated because of too low temperatures resulting from light load operation or too rich a mixture.

Brown or black varnish on piston side below rings is baked oil caused by combustion gases blow-by. Improper oil or poor ring sealing is the cause.

Very light scoring of the piston skirt is likely from foreign material passing through the engine. It does not suggest a problem in the engine and piston replacement is not required.

Always check piston to cylinder wall clearance to make certain the wear limit has not been exceeded.

Deposits should be removed from the piston dome and cylinder head using a wood or plastic scraper. Excessive deposits collection will increase the compression ration and reduce heat transfer. 

Ultralight Aircraft News Magazine