Just thought i would add this in to a question that don’t look like it was answered, and for the people that find this in the future looking for the same.
I have actually come here looking for an answer to a problem after getting the skeletal mesh back into the engine, ANYWAY, I was trying to get the advanced vehicle out of UE4 to Blender then edit it and imported back into UE4, BUT kept getting the same Multiple Roots found error, No matter even if i just imported into, then exporting without changing anything at all ?,
So it did seem like Blender was adding something.
But after trying to delete this and that and every kind of importing/exporting configuration, AND Days of searching, I found someone (can’t remember who, and at the time thought his/her
answer didn’t sound like the answer, but thought i would try it later kind of thing), He or She mentioned something like, Have you checked your 3d editing program is SET to METRIC And not IMPERIAL ?.
So lo and behold later i thought of checking Blender (Haven’t done much with Blender yet 
And yes it was not set to Metric, So changed it and only exported the armature and mesh like loads of people here tell ya too, And it worked, No more multiple roots error, So Blender and probably 3ds max ect Don’t add an extra root bone and nor does UE4 Add on export like i have read too.
I hope that helps someone out there ;), And after finding that answer and working out that you have to import it scaled up to avoid the wheels sinking into the ground problem ?, I hope to work out why now the car is the scale i want and sits on the ground properly BUT now it seems (From my very limited knowledge) like the vehicle component is still the original size and seems to need scaling up ?, Because the wheels seem to be going at a different speed to what the care is going Plus the turning circle is alot smaller to scale of the car (car turns in a smaller circle to what the wheels could possibly be turning the car in ??)
Anyone ?
