The ornamental design for a rearportion of a motor grader, as shown and described.
FIG. 1 is a right, front perspective view of a rear portion of a motor grader showing our new design;
FIG. 2 is a right, rear perspective view thereof;
FIG. 3 is a left, front perspective view thereof,
FIG. 4 is a left, rear perspective view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a rear view thereof;
FIG. 7 is a right side view thereof;
FIG. 8 is a left side view thereof; and,
FIG. 9 is a top view thereof.
The broken lines of the figures showing additional portions of the motor grader are included for the purpose of illustrating environmental structure and form no part of the claimed design.