Thread: ROTAX Compressions

Request opinions! I'm trying to figure out how or why my mechanic derived at compressions in the log book:
#1 - 90/90
#2 - 89/90
#3 - 90/90
#4 - 88/90
ROTAX manual says:
"The leak down or differential compression test requires a bit more specialized equipment including a source of
compressed air. A pressure of 80 - 87 PSI is applied to each combustion chamber (whilst at top dead center on the
compression stroke) through a 1mm orifice. The amount of leakage from the combustion chamber can be measured by
measuring the pressure in the cylinder. If a low pressure is measured it is easy to identify the source of the leak by
listening to the carb, exhaust or oil tank for air escaping. The maximum permissible loss is 25%."

Guess he didnt read the manual. On the other hand they are near what would be expected, these 912's are tight. Rotax used to say 87psi was the base number now they have changed that some. Most T C ed engines use 80 psi. Perhaps you might want to point that out to him.

Thank You! I'm going to be operating out of St Louis area. Where is your maintenance operation located?