About this 3D model

This dead simple part is just a 50mm long bar with two M8 holes. One end carries a 608 bearing and the other fits onto the lower front rail next to the motor mount. Install as per the photo. You shouldn't need fender washers on the bearing (assuming your belts are properly straight) but don't forget the thin washers to allow the bearing to rotate freely. Once fitted, simply adjust to the correct angle to take up any slack in the belt (don't make it too tight or you'll be increasing the load on the Y motor) and then tighten the right-hand nut. Hopefully that should help to eliminate backlash on your Y axis