I replaced my burned out original blade motor with the aerobatic upgrade motor. I believe the pinion gear is different on the aerobatic motor. Does the main shaft gear also have to be replaced to mesh properly with the aerobatic motor's pinion gear? It works and flies fine but seems to make a bit more noise and doesn't spin as freely. Thanks.

The pinion gear you had on the original motor was a 10 tooth and you now have a 9 tooth gear which will speed up the rotor blades. The 9 tooth pinion is made for the sim blades but will speed up the RPMs of the flat blades if you are using them and that is not a problem. That is the noise you are hearing (increased RPM). You will then be ready for the sim blades.
oppie

Actually that's not the case oppie. The head speed is slower, not faster, with the 9T motor. I assume Horizon does this since a 3S lipo will speed the motor up, and they want to run the same head speed. Now, an 11 tooth motor will turn the blades faster, but a 9t is slower, notwithstanding what higher/ lower voltages do to even things out.

To the original poster: did you correctly set the gear mesh? There is most certainly enough slop in the screw holes to set up the mesh too loose or too tight.

I'm sorry I should have added that you don't have to change the main gear. The gear mesh is the same for the different pinion gears available for the Blade, the 10, 9 and 8. If you are experiencing a tight gear match you might have it to tight and you don't want to burn out another motor. The way you test this is to cut a paper 1/4" x 2" and place it between the pinion gear and the main gear, move the main gear so it will move smoothly with out binding. That will give you the proper pressure.
Don