Milt,
unproductive comments deleted
Think about it. You have two engines spinning that are equal distances from the center of mass which basically cancels the effect of the engines spinning. If one of them stops, the rotating mass will cause yaw because the engine wants to roll to the right or the left depending on if you are in a GE or a RR.
Most of us had toys that taught us this as a kid. Get something spinning very fast and it is hard to hold still.