Right 4-Engel elements of a group

We prove that the set of right 4-Engel elements of a group $G$ is a subgroup for locally nilpotent groups $G$ without elements of orders 2, 3 or 5; and in this case the normal closure $^G$ is nilpotent of class at most 7 for each right 4-Engel elements $x$ of $G$.