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:
- Take the main gear out and remove the auto-rotation gear
- Remove the one-way sleeve, unscrew the oneway bearing housing, now remove the one-way sprag bearing
- 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.
- Re-shim the main shaft at the collar if required.
- Done
This morning was perfectly still and clear again in London so I was out with my Trex 600 EP before work. The Rhino 4900 6S 20C batteries continue to impress me. This was the forth cycle today and they are still awesomely powerful with no sign of puffing or fatigue what so ever 
I noticed on the second flight something hit the blades, like a bug or something, but it was really just my subconscious that noticed it. After the third flight I noticed a slight buzzing coming from the tail and sure enough one of the screws that bolts the boom-support to the main frame was missing . Needless to say I considered myself very lucky and called it a day.
It’s not often there are no warning signs before things go terribly wrong
Yes that’s right I said it today was choppatasic, super still air this morning with good visibility, perfect conditions for 3D.
I’m up to my third cycle in on my Rhino 4900mah6S 20C packs and they are loving life in the Trex 600. I was practicing funnels tail down both upright and inverted…I just need more stick time.
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
Sunday turned out to be a good day for flying down at EMHC, I ended up getting some good piro work in. Towards the end of the day after about 5 liters of fuel I lost the heli on a high speed inverted backwards circuit. I over corrected and shaved off too much headspeed to re-correct and ended up in the long grass/hedge at the edge of the field. Fortunately the headspeed was low and grass long (thanks to the groundsman) so damage was minimised. At this point I remind myself why I invested in a Trex700, smile and order some more parts. The moral of the story is crashes happen at the end of a long day, so quite while your ahead
For me the moral of the story is crashes happen at the end of the day so quite while you’re ahead.
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