Ok. first post here. hope to be glorious 
So. my workaround was:
change grid size in blender to 100 ( hotkey N → display → gridfloor → scale)
the exported the mesh and armature without any sort of animation
and imported in UE4 as a skeletal mesh, but without the “import animation” selected
Now, back to blender and create your animation. When exporting just use the same method but deselect the mesh and export only the armature
finally, go to ue4 and import the animation and select the armature from the first export
cheers