Gidday Jim
With regards to 912 uls gearbox problems, I'll pass you some actual facts that you and other readers can view and comment.
The following engines and aircraft are ones that I maintain and have done the gearbox repairs on. Very rarely do I find the friction torque out of tolerance, if I do it has been on the 80 HP 912, no vibration but hard to start problem. Most of them run on aeroshell sport plus and oil changed at 50 hrs and only run on 95 PULP. I have found the 80 HP 912 don't appear to have these gearbox problems.
Engine 1, TL sting aircraft, 3 blade wood comp propellor, 912 uls engine, problem, owner experienced excessive vibration on low power settings, turning on final, TT around the 600 hr tachometer time, friction torque as per Rotax MM, repair was to replace worn gearbox dogs, problem solved
Engine 2 Tecnam p92, 3 blade airmaster prop, 912 uls engine, same problem as above aircraft, 350 hrs flight time, replaced dogs, problem solved.
Engine 3. Fox-bat A22 3 blade Kiev prop, 912 uls engine, around the 600 hrs Tachometer time, same vibration problem, same repair and problem solved.
Engine 4. CTLS 3 blade Nueform prop, 912 is engine, 126 hrs tachometer time, severe vibration around the 4-5 k rpm 18"- 24" man pressure settings, replaced dogs, problem solved, managed to get parts under warranty.
Engine 5. Tecnam p92, 2 blade GT propellor, 912 uls, 1200 hrs flight time, 3 complete gearbox overhauls, this includes on each oh dog, gears, disc Spring washers, washers, front bearing and preload set as per Rotax MM. This ac does operate in a flying school and has its oil changed every 50 hrs with aero shell sport plus and friction torque checked at 100 hrlys. Prop dynamically balanced,95 PULP, As an experiment this engine was derated to about 80 HP by putting a simple rudder tube spacer on the cockpit throttle shaft to try extend gearbox life but gearbox started vibrating around the 400 hours flight time. Experiment failed.
Engine 6 Cub replica, 3 blade prop, 912 uls, 600 hrs, same vibration, replaced dogs, problem solved.
The other 3 Rotax 912 engines that I look after have not yet reached 100 hrs, so far no gearbox problems.
