You have work to do.
Remove the tailboom, supports and tailrod from the servo.
This way you can put the G4 on the back off the skids and the boomholder. The engine is now upwards. Remove the engine from the
Put a thin piece off paper (carbonpaper) between the pinion and the main gear. Now press the pinion hard against the main gear and tighten it.
Next you slide the engine over the engine mount till the startershaft going into the one-way bearing. What you look for is if there is a space between the front off the engine flang and the engine mount or at the back. You can't move the engine mount so you have to play with the pinion. But better is to (if not correct) put a piece of brass foil between engine and mount. This is what i had to do.
If you don.t do this the bearings of the bell will wornout quickly or the clutch will break.
TT G4, YS 96/120 srx, Beastx, cgy750