Assembly and disassembly verification plays an important role in Product Lifecycle Management (PLM). Mass customization and personalized production require greater agility of industrial manufacturers, and consequently the time consumed in assembly processes (which often dominates costs) is of growing importance. Narrow passages which commonly exist in assembly tasks become a bottleneck in the assembly planning process reducing the time saved by using virtual assembly. In this paper, we present a novel interactive motion planning methodology for virtual assembly and disassembly operations. In our method, user's manipulation with force feedback device in difficult scenario is liberated by relaxing collision constraints. The rough path is retracted by our random retraction method and then connected by BiRRT algorithm. For each user's operation, a path successfully passing through the narrow passage is presented, or geometrical interference information in failed case is provided for motion re-planning and design modification. Significant improvement for trajectory planning of non-convex object is observed in challenging 2D scenarios with narrow passages.