Don't follow Estes instructions to use external masking tape! The burned residue is awful!

Friction fit your motor to the upper stages in the normal way with tape on the motor INSIDE the motor tube, safe from burning.  Make sure the tape goes all the way to the end of the motor to help the motor stay in the manifold during flight and ignition of the upper stages. This burned residue, difficult to remove by itself, is hiding a more insidious problem: the balsa was burned also. My rockets have since been treated with high-temperature silver paint in an effort to resist upper-stage burning. Hope it works!