I could not reproduce your problem, but I’m on version 4.12.5. Do you have “acceleration change” activated on the add torque node? Ony thing I could imagine is that if it is activated that the vector length of 4800 units is very high then. So that the sphere spins with the framerate you get on the scene and doesn’t appear to spin.
btw. if you are able to reproduce this. The best way would be to write down every step to get to the bug and then post it in the “bug report” section of the answerhub. right now this is in the “Using UE4” section and won’t get the needed attention.