The main gear is easy. you don't have to take much apart at all. undo the links from the balls all three servos let them lay. then under the FRAME (top) under the swashplate area is a wheel coller on the main shalt loosen that. ( now there will be play a little) undo the bolt hold the main gear on the shaft (tap out) NOW have someone hold the heli upside down firmly and tap the shaft out from the bottom (easy does it) use blowdryer for a moment and remove the gear .

Now putting it back togeter is easy too remember the d shape in the gear and bottom of shaft
line up holes in shaft and gear slide it on (tight) blowdryer a bit and boom she slides right on.
bolt throught hole shaft in bottom frame slide up the wheel coller tighten add links back to the balls everything should still be tracking well and your gear is installed.

about 15-20min job

Chaseman81