The scene root is not staying with the mesh I assigned to it. The Mass mesh falls but the scene root, and by default the top of the spring does not move. The impact Mass on Wheel causes Wheel to bounce, but that is all it does.
Resolution:
Typo in the FName on the Mass constructor. Consequently it appears that the FName in the code, and not the displayed name in the BP is what the Physics Constraint attaches to.