I just replaced my Velineon system with a CC 3800kv setup. I ordered a 14t pinion (Traxxas #5640). It doesn't seem like the pinion is meshing properly with the spur. I'm getting a major grinding noise. With the the motor removed, everything is smooth. With the motor in and the pinion gear not tightened to the motor shaft, I get the grinding noise.

Is this the right pinion? It a 14t 32p with a 5mm bore.