Motorcycle tyre valve stems come in two styles -- screw-in and press-in. Both types serve to seal around the valve stem hole in the rim and house the valve stem core, which holds pressure in the air space inside the tyre/rim assembly. Press-in stems are rubber assemblies that are held in place by the interference fit between the stem and the rim hole. Screw-in stems are threaded metal assemblies with a rubber seal on the inside of the rim and a locknut that clamps the stem in place and compresses the inner seal against the inside of the rim. Both types are easily replaced with a minimum of speciality tools and training.
Removing the tyre
Insert the valve stem tool into the valve stem and engage it in the notches in the valve core. Unscrew the valve core in a counter-clockwise direction to release the air pressure in the tyre. Remove the core from the valve once the pressure has bled off.
Loosen the rim lock (if applicable) and remove any wheel weights from the rim. Lay the tyre on its side. Break the bead on the tire by pushing the tyre sideways on the rim using firm pressure. Beat stubborn beads with the rubber hammer to overcome the bead/rim connection.
Install the rim protectors and begin peeling the upper bead off of the rim. Once the upper bead is free, repeat the process for the lower bead, coming up off the same side of the rim as the upper bead.
Replacing a press-in valve
Insert the valve stem puller into the rim side of the stem. Pull the stem through the inside of the rim and discard it. Inspect the rim valve hole for damage or deformities.
Insert the new stem through the hole in the rim. Screw the puller onto the threads on the stem and lever the new stem into place in the rim. Remove the valve core from the new stem and reinstall the tyre. Seat the beads of the tyre with air pressure, then allow the pressure to bleed off. Insert the valve core into the stem and tighten it down snugly with the valve core tool.
Inflate the tyre to manufacturer's specifications. Balance the tyre.
Replacing a screw-in valve
Remove the locknut from the valve stem. Push the stem back through the rim and inspect the rim hole for damage.
Insert the new stem into the rim hole and insure that the rubber seal on the inside of the rim nests into place in the rim. Reinstall the locknut and screw it down finger-tight, then torque it lightly with the crescent spanner. Remove the valve core with the valve core tool. Reinstall the tyre and inflate it to seat the beads. Allow the pressure to bleed off then reinstall the valve core.
Inflate the tyre to manufacturers specifications. Balance the tyre.
Tyre balancing takes special equipment and training and should be left to a professional service department.
Use caution when removing the valve core with pressure in the tyre. Removing it from the stem before the pressure has bled off completely can eject the core with great force and turn it into a dangerous projectile. Wear safety glasses during this operation.