Non-Uniform Air Gap and Motor Performance

Depending on where and how much of a variation in your air gap this will have one of three results.

1. No appreciable effect (gap not part of any magnetic field path).
2. Theoretically permit you motor to run very slightly cooler (more air cooling of core).
3. Decrease your actual torque from the theoretical peak torque (gap between rotor and stator laminations).

Now there are several silly ways one can add an inappropriate air gap that can have catastrophic results for your motor. But I don't think that you're asking about what a TIN drill bit and a drill press can do to your motor.

I will leave the electrical performance question to others better qualified.

However, one thing that you should be aware of is the damaging effect of "magnetic" vibration in a motor caused by a non-concentric air gap.

Magnetic fields cause radial forces which are usually balanced. Non-concentric magnetic fields cause imbalanced radial forces.

These magnetic radial forces are inversely proportional to the air-gap and proportional to power (I²). As this vibration is caused by the rotating magnetic field it will have a frequency of 2 times line frequency. (Not a multiple of rotating speed as would be caused by say misalignment.)