The clutch bell bearings have started to get quite knotchy on the Aurora (100+ flights) so I decided to replace them. It turns out only the middle bearing part: AV00-200-216 needed replacing (that’s the larger of the bearings which sits just above the pinion) which presumably takes most of the force. A tip for any one needing to replace clutch stack bearings is:
- Drop the engine,
- Leave the ratio plate in place but remove the clutch block bearings (x8 bearings)
- Undo the starter coupler set screw and remove the starter shaft by sliding it down
- Slide the top bearing block up out of the frame
- Slide the lower bearing block and clutch-bell down out out of the frame
The stock Aurora sprag bearing needs to be lubricated in order for it to function and with stand the abuse of 3D flight. I’m not entirely sure what type of grease the bearing is packed with by default but it lasted about 10-15 flight before I noticed the sprag slipping (the governor was hunting wildly in 3D flight). The simple fix is to flush and degrease the bearing, just use nitro fuel, WD40 or similar. You will need to take the plastic bearing side case off (careful of the tiny springs inside) in order to degrease the bearing. Once the bearing is degreased soak it overnight in Automotive Transmission Fluid (ATF) then replace the plastic side case and your done.
ATF is very thin and will eventually work it’s way out so regular lubrication is required but that’s really just a maintenance thing. Future re-lubrication can be done whilst leaving the sprag in the maingear housing and just removing the plastic side case and dabbing ATF on with an ear cotton bud. The bottle pictured below is the ATF I used and is available at most auto-stores and service stations in the UK for about £5