Posted by John Swensen on June 24, 1999 at 16:02:52:
In Reply to: another rotary question posted by Mark C on June 24, 1999 at 14:26:48:
Clanking sounds like the bearings. Either remove the linkage connection to the second
valve or depress the second valve key part way down, then grab the stop arm and try to wiggle it. If you see it moving, and especially if you hear the same clanking, your bearing is loose. Thicker oil on the bearings (you are applying oil to the bearings, aren't you [a drop at the spindle-bearing junction, pull the slide to suck the oil in, then unscrew the back cover and repeat for the lower bearing]) can help dampen things, but too thick will make for sluggish action.
If the bearing is the problem and thicker oil doesn't work, a good repairman will have a tool to swage the bearing down onto the spindle, after which the spindle can be very carefully lapped for free action.
Another possibility is that the bottom end plate is too far out, opening up the clearances too much. Seating this bottom plate further in may work, or may not, depending on the design and assembly of your horn's valves.
Another, likely possibility, is slop in the linkage, especially right where it attaches to the rotor stop arm. Without seeing your linkage I can't offer too many suggestions, but heavy grease at the end might damp the clanking.
A cheap source for the rubber bumpers is a neoprene O-ring with a suitable cross-section (that's what O-ring types call the thickness of the O-ring). You want a cross-section slightly larger than the diameter of the hole for the bumper, so that it is a tight fit. If you buy a 3" or 4" O-ring from a bearing supply place (they may just give one to you), you can cut lots of bumpers with a razor blade. I have never heard of neoprene getting hard with use on a tuba, however. Cork is supposed to be quieter than neoprene, and wine and champagne corks work well, although special cork material in round sticks can be had from Ferree's or from a friendly instrument technician.