On many occasions I get asked the same question: “What happens when using AVGAS in the Rotax 912 / 914 series engine?” The Avgas currently available, as we all know, has Lead in it and when used it will leave Lead deposits behind. The Rotax recommended 25 hourly oil changes will make sure that these deposits will not cause any harm to the engine or gearbox. As per schedule the gearbox will need more frequent removal and strip down to remove the Lead residue from the Slipper- clutch (if engine/gearbox is fitted with such).
The Oil tank should be inspected as per Rotax schedule and the Oil /Lead deposits removed from the bottom of the tank. The pictures : show a engine gearbox slipper clutch assembly & oil tank full of sticky grey Lead sludge. This engine has been running on Avgas only, & only 100 hourly oil changes were made using a non compliant oil. This resulted in major Lead deposits throughout the entire engine. The Lead in the Slipper clutch will make it stick when it is intended to slip. Hence causing damage to Starter clutch, Gearbox & Doghub, Bearings, not to mention a prop strike scenario. All just to save a few dollars on oil. But paying heavy for related repairs later with an engine not running right !!! So if you use less than 25% Avgas during your 50 hourly cycle there is no need to worry. If it is more : then do the right thing !! Next time we will take a closer look at the current MOGAS and the in-flight issues it can cause !!!! – Fly save, cheers Ole H. AAK