I've noticed that if you try to set the Rotation of a single part in a welded model, it breaks the joints rather than rotating the model with it. Is there any way to rotate an entire model to a desired Rotation?
Models can be manipulated just like regular parts, except for the fact that they use methods. You might want to keep these somewhere in case you forget:
Click and drag over the parts you want to rotate, then enter the amount of rotation you would like on the model. Also make sure you have the parts grouped together. Hope this helps!