The ornamental design for a lock for locking beltgears in position, as shown and described.
FIG. 1 is a perspective view of a lock for locking belt gears in position showing my design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a reduced perspective view thereof, with the claimed design shown in use, and with the broken line showing for illustrative purposes only and forming no part of the claimed design.