The adjustment screws on the rear caps of Miraphones may be used to take up a little axial slack in the "thrust" direction, but that is a temporary measure. The true thrust bearing surface on rotary valve is a collar right around and at the base of the rotor shaft, front and back. If there is slack there, then the outside of the rear bearing plate (not the screw cap, but what's under it) needs to be turned down a bit so that it sits deeper in the casing.tubafreaks7 wrote:I have never been shown the propper way to oil a rotor valve. I've researched it enough to figure out the various methods but still have a few questions:
-Is the thrust plate on a Mirafone 186 supposed to be flush with the valve casing, and are the little screws in the caps for oiling or are they supposed to touch the valve, like a set screw? Is Holton rotor oil heavy enough for the bearing surface, or is it just to be used on the face itself?
On valves that have no slack, you drive down the rear bearing plate as far as needed to adjust the thrust slack, and as straight as needed to prevent binding. In my experience with my own instruments, that will not be driven all the way down to the shoulder on the inside of the casing. Thus, the rear bearing plate may or may not be flush with the rear of the casing. But if it stands proud of the casing, you might "adjust" it when tightening down the rear caps too much. I think the better instruments are made to provide the correct thrust slack when the rear bearing plate is driven all the way home. The rear caps then tighten down normally. My Miraphone (which has a lot of wear) has a little more slack than I would like with the rear plate all the way home. But both the Cerveny and the VMI stencil that I owned in the past could not tolerate having the rear plate driven all the way home, and would bind if I tightened the rear caps too aggressively.
You should use a good, light machine oil, applied under the rear cap at the interface between the rear rotor shaft and the bearing plate, and applied under the stop arm between the front rotor shaft and the bushing that is machined into the casing. A needle oiler works best. Hetman's rotary valve oil comes with a needle applicator that is perfect for this. This oil should be thicker than regular valve oil if you want it to prevent wear.
The rotor bodies and the casings should not need oil for friction because they should just not touch. But they need oil to provide a good seal and to prevent corrosion, and regular valve oil squirted down the leadpipe occasionally while working the valves will accomplish that.
Rick "who uses the same rotor oil for the linkages" Denney
