check out the answers (not the selected one) on https://answers.unrealengine.com/questions/350406/blender-to-ue4-amaturebone-rotation-scale-problem.html
i believe the problem is the scale, i also had to change scale on blender for Physics body to work, maybe its the same problem
for reference:
"I had this problem with the default scene settings. After changing the scene units to meters and 0.01 scale (and resizing everything) things are now working perfectly. Are you sure you have applied the transforms in blender? Scene scale should be 0.01, armature scale should be 1.000 and the mesh scale should also be 1.000. The z dimensions of your mesh should say 2m or something in that ballpark. No scaling in the fbx export settings. This should fix the issue assuming you’re using the latest blender version (2.76b at this time). "
- cyaoeu