This is my custom motor mount made for my electric longboard. I recommend printing it in ABS or some PLA with carbonfiber (15-20%). The mount consists of a mounting plate, a locking ring and a shield. I have made a version of the mounting plate without shield.
To make sure the motor mount doesn't bend I have made room for two solid 3mm*80mm steel rods, that slides in from the tip of the motor mount. You can read more of the motor mount here: http://www.electric-skateboard.builders/t/the-orange-firefly-turnigy-sk3-6374-192kv-10s3p-25r-vesc-6-3d-printed-enclosure-motor-mount-custom-deck/21639/19
The mounting plate needs spacers between the motor bolts and the plastic mount. I have made some in aluminium on my CNC that fits right on, however I believe a standard washer would suffice.
My setup uses a wheel pulley with 40T and motor pulley with 15T - and my belt is a 295 mm HTD-5M.
Hope you enjoy :-)