The effect of rotationally inelastic collisions on the orientation of the angular momentum is investigated for C2H2 (nu(2) = 1, j). The orientation of the angular momentum in initial rotational states j(i) = 7 to 13 is prepared by stimulated Raman pumping using circularly polarized light and S-branch transitions. After allowing an appropriate time for collisions to occur the orientation is probed by laser-induced fluorescence in the (A) over tilde (1)A(u)<--(X) over tilde (1)Sigma(g) transition. For acetylene the theoretically calculated and the measured initial orientation, A(0)((1)), ranges between 0.7 and 0.9. A substantial part of the orientation is conserved in rotationally inelastic collisions, which could be measured up to \Delta j\ = 6 with sufficient signal-to-noise ratio. These results are compared with previous measurements on the conservation of alignment in collisions. Rotationally inelastic collisions with \Delta j\ = 2 result in an average rotation of the orientation vector by about 30 degrees. The amount of orientation that remains after a rotationally inelastic collision is found to depend primarily on \Delta j\. A Delta m(j) = 0 propensity rule often used in models of rotational energy transfer is found to be inconsistent with the measurements. Also a model which proposes a minimum change of the classical angle phi between j and the quantization axis does not reproduce well the experimental data. Finally, a microscopic model for Delta m(j)-transitions is presented which reconciles both alignment and orientation measurements.