Turning down motor shaft

[Brow]

I need to turn down a Neu brushless motor shaft from 8mm to 5mm. I thought it was going to be easy to remove the rotor and do it in a lathe but I can not find out how to remove the rotor. Can has no screws holding end bells. Neu suggested sending motor to them and get rotor changed out. Cost and shipping it from Australia and back is not cheap.

I have thought about running motor up on ESC and using dremmel/file/cutting bit to turn it down but can't find an easy way to do it without using the radio to control the esc.

I have seen brushless motor checkers and speed passion has a system to do it without the radio but both are expensive.

Any ideas out there?

Thanks
Brow