The ornamental design for a lawnmowerpowerhead, as shown and described.
FIG. 1 is front perspective view of a lawnmower powerhead according to the present invention.
FIG. 2 is a rear perspective view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a left side view thereof.
FIG. 6 is a right side view thereof.
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
Any elements shown in broken lines in the Figures form no part of the claimed invention, and are instead included to show environmental aspects of the claimed invention.