The ornamental design for a topcover for an internal-combustion engine, as shown and described.
FIG. 1 is a first perspective view of a top cover for an internal-combustion engine, showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a right side elevational view thereof; and,
FIG. 7 is a left side elevational view thereof.
The broken lines shown in the drawings illustrate portions of the top cover for an internal-combustion engine that form no part of the claimed design. The drawings include grayscale surface shading which illustrates contour, not any particular color.