Been working on the "Ultimaker 2 Aluminum Extrusion 3D printer" and had some issues with the motormounts: The original maker did an outstanding job, but I bumped into some didifficulties and made some changes. Issues/Changes Y axis Mount (motor that drives the X axis) 1) Belt was rubbing against part of the motor-Mount, so removed a piece. 2) I enlarged the areas around the screws to make room for washers to spread the stress caused by the screws on the Mount. Issues/Changes X axis Mount (motor that drives the Y axis) 1) The 2 screws holding the motor in place, located close to the aluminium extrusions bit into the extrusions. 2) I moved the entire assembly 2mm farther out to mitigate the above - this makes room for the use of washers as well. 3) - After the above change, the belt bit into one section of the motor-Mount, so I removed a small piece/corner. Print with 100% infill to make it solid. I used 0.2 layers, but I guess any would do. You might need to drill out the holes for your screws to fit in. Use support on the X axis Mount (motor that drives the Y axis). Use 3-4 times z-distance as your layerheight - I use 0.7 distance with 0.2 layer-height.