UK Heli Log

When I first built the Trex 700 one of the many issues I found was the main gear moves several mm up and down (in addition to all the meshing issues).
I simply put it down to poor manufacturing tolerance and accepted it, but as it turns out this movement up and down is due to poor assembly of the “main oneway bearing assembly”.

After seeing several gears strip at the field in the weekend, this up and down main gear play was debated and someone (Peter – EMHC) explained how they removed it.

This is just another weak link in the chain that is the Trex700 drive train, which can be completely corrected, this is how.

Bearing Alignment Before Adjustment (NOT flush with the top of bearing housing)

Bearing Alignment After Adjustment (now flush with top of the bearing housing)

Steps to correct bearing alignment:

1. Take the main gear out and remove the auto-rotation gear
2. Remove the one-way sleeve, unscrew the oneway bearing housing, now remove the one-way sprag bearing
3. Get a 15mm or similar socket (from a socket set) and a hammer, use the socket and hammer to reposition the bearing flush with the top of the oneway bearing housing.
4. Re-shim the main shaft at the collar if required.
5. Done

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