I created a mesh in Maya 2015 that was part helix and part my own design . I deleted the caps on the helix and used loops to hold up the tubes. Upon exporting to FBX and then converting to FBX 2013 the mesh was imported to UDK. The mesh looks fine except around the previously capped area. The polygons do not display if you view the mesh straight on but do display if you view them from the side or above.
First thing, you mention UDK and I want to make mention that the AnswerHub is specifically setup for issues regarding Unreal Engine 4.
Regarding FBX 2013 - UE4 uses FBX 2014 now.
Something to check on your model is to make sure that all your Normals are facing the correct way for your mesh. If you have any flipped faces this will cause the mesh to not be visible since the back face is being culled out.
If you’re still having issues make sure to post a screen shot.