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
Gear mesh on the 700 is very important as the main gear has a 0.7 mod (fine gear mesh normally found on 50 size heli’s). In order to mesh the gears correctly you need to adjust the main gear to pinon gear gap and also auto rotation gear to tail gear gap. This can be achieved by grinding down the nubs on the clutch block and plastic tail case (see photos). In addition you will need to replace the screws with standard non-specialty button head screws and use the specialty washers from the Trex 600. This will need to be done for clutch block, plastic tail case and engine blocks. This will give you enough play to adjust the mesh.
Upgraded Metal Clutch Block with Grounded Metal Nubs
Tail Case with Ground Plastic Nubs
Well I did end up fliying for a brief moment today in between showers, all be it very windy. Turns out my tank is leaking quite badly due to the stupid second stopper in the middle of the tank.
Time for a mod…
I drilled a hole in the stopper and placed a 3mm button head screw and washer. On the inside another washer and nylock nut. I also used an old o-ring from a old 91 carb base and placed it on the outter side of the the stopper. I guess I’ll find out if it works next flight.
Everyones favourite, so easy and convenient.