I have a friend of mine that has a trex 450 Im not sure the version off hand, its not a v2 because he has plastic parts that are metal on the v2. He has been flying his heli all week but after noticing a deformation in his one way bearing shaft he decided to replace it and his main gear. After he replaced it he noticed his main gear was not meshing with his tail drive gear assembly. I took a look at his heli and did not notice anything unusual. the main shaft was not bent, the tail drive assembly was in tact and secure to the main frame, as was his main shaft bearing blocks. I cannot see any reason these gears would not mesh. I compared it to mine and there was the same distance between the larger gear and the tail shaft assembly, also the same distance between the motor mount and the smaller main gear. the main frames are in tact and no screws are loose, all together it seems to be a freak of nature. At first I thought he had bought a smaller gear than waht was originally on it, but it is the same size as mine. Can someone plz help, has this happened before??

If he has the white plastic gear(22T) on the tail drive assembly he needs the 109T autorotation tail drive gear. The newer gears are 25T and 106T.