I personally wouldn't run a motor without a thrust bearing. Like Bob said there is a lot of force on the end bell of a motor without one and to have a end bell pop off is pretty bad and will most likely kill your ESC too. On my Fiegao and hacker motors I like to put the thrust bearing up against the motor but with the Neu style motors with the longer shafts I build my mounts so that the bearing is up against the mount itself. You will be happy you spent the $20 at OSE on the thrust washer after you lose one end bell on a motor.