The ornamental design for a motorcycleswingarm, as shown and described.
FIG. 1 is a right, rear perspective view of a motorcycle swing arm showing my new design;
FIG. 2 is a left, rear perspective view thereof;
FIG. 3 is a right side elevational view thereof; and,
FIG. 4 is a left side view thereof.
The broken line showings of the circle in FIGS. 1 and 3, and the hardware in FIGS. 2 and 4 are for illustrative purposes only and form no part of the claimed invention.