How to Fix a French Horn Rotary Valve

Place the horn on a workbench with the front side facing up. Use a flat-head screwdriver to remove the small valve cap screw on the front side. Flip the horn over to the back side. Use a screwdriver to remove the screw attached to the linkage arm. Unscrew the linkage receiver screw next to it, which is also on the top.

Place a thin, 2 millimeter center punch into the tiny hole where you just removed the receiver screw. Use a hammer to tap the punch until the small bearing plate comes loose and falls off on the other side of the valve. Put the bearing plate upright in your hand and make sure the small check ball is seated in the middle.

Pull out the small rotor from the casing. Clean the rotor with valve oil and a soft cleaning cloth. Clean the inside of the small rotor case with oil and cloth. Smear a thick film of oil inside the case and on the rotor body. Put a dab of oil on the check ball.

Place the bearing plate back on the case and push it in just enough so it seats in the case. Place a hollow plastic block over the top of the bearing plate and tap it with a hammer until you see the bearing plate seat flush in the case. Use a screwdriver to tighten the valve cap screw.

Flip the horn over and gently push the valve stem to make sure it moves freely. Align the linkage shaft with the receiver hole and insert the screw in by hand. Tighten the receiver screw with a screwdriver.

Attach the linkage receiver with the linkage arm and tighten it with a screwdriver. Make sure you put the washer under the screw. Dab some oil on the linkage lever joint where it connects to the key. Insert an eyedropper filled with rotary oil through the mouth piece and blow hard to coat the inside of the tube and rotor valve spindle. Turn the horn in several degrees of rotation to spread the oil inside. Test the instrument.