When I import my FBX mesh into UE4 it comes with cracks

Hello. I am having a hard time importing meshes with a good amount of faces. If I import them with low resolution I won’t have any issues but then looks very poor quality. When I smooth them and Import them as an fbx some of the faces disappear. If I import as an OBJ it works but the location of the mesh it’s totally crazy! I’ve tried to triangulate it as well and nothing works. I am attaching some images.