Rotor spindle oil is an essential lubricant for maintaining the smooth action of all rotary valves, especially those on French horns and trombones with valve attachments.
Yamaha has drawn upon decades of experience to create a line of fully synthetic oils designed specifically for musical instruments.
In addition to producing a smooth action and a fast response, their oils protects valves and valve casings from corrosion with a long-lasting coating.
Note: this product is equivalent to the bearing oil produced by other manufacturers, and is used in a similar way.
Modern French horn rotary valves require three different grades of oil. From thickest to thinnest they are: bearing oil, linkage oil and rotor oil. Apply the first two each week, if you play regularly. When a valve become sluggish, drip a tiny quantity of rotor oil directly into the rotor casing, having first removed the valve slide to allow access.
For reference, a maintenance schedule recommended by the Rosehill workshop is included alongside the product image(s).