Someone wrote that only 20 % of 912 iS owner have this issues. Do you know how it is possible ? Gearbox on iS are not all the same ?!
I have the same question. I just rolled past 350 hours (2016 engine) with no apparent issues with my gearbox. I am now hyper sensitive to any vibrations. Hope they figure out a solution soon.
Historically engineering aircraft engine gearboxes has been a huge challenge. As the engine manufactures were producing more and more powerful engines for the second world war they introduced more gear boxes because the massive increases in HP were achieved in part by running engines at higher RPM. Thus gearboxes to keep props in proper RPM. From that time gearboxes became the stone around the necks of design engineers. The gearboxes required frequent replacement for the same reasons they do today. There are now engines used on general aviation a/c that some owners keep a spare gearbox on hand to avoid extended down time. Rotax has a problem with the iS gearbox .I feel confident that Rotax is addressing the problem and will provide a solution. I purchased my 912iS before the modification to Sport. At about 40 hrs engine time Rotax came out with the sport upgrade which increased the torque a significant amount. I installed the sport mod and then started having vibration issues. I often wonder if I had kept the engine original if there would have been vibration problems. Bottom line for me is have faith in Rotax that the issue will be resolved. Keep in mind that even the gearbox used on the carb version 912, require an inspection at specific hours depending on the use of Mogas vs low lead fuel.
I’m at 90 hours on a new installation and the dreaded vibration has started. In climb when the prop is under load, the engine is smooth. Once level and accelerating, the “buzz” begins between 4900 rpm and 5400 rpm. At times you can stop it by slowing down and slowly accelerating back to cruise speed. You can begin to slowly hear its onset and then it’s a buzz you can hear and feel. All engine indications remain normal and in the green. It started right about at the 65 hour mark and has gotten progressively worse. It’s almost like an aerodynamic buzz or a fluttering inside the cowling. I’ll be checking anything that might be beginning to buzz under the cowl. I hope there is a real fix in the works as this is totally unacceptable in a aircraft engine....
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