Re: causes of rotors clicking - and misdiagnoses
Posted: Wed Jun 20, 2018 8:15 pm
A couple months ago, I worked on an elderly gentleman's tuba. It was a Chinese copy of the B&S 'Sonora' BBb tuba. I believe the man bought the tuba cheap from a now-defunct west coast music store. The only engraving on the tuba was "Infinity" on the bell.
The tuba itself actually played very well; nice deep sound, in tune, good response. But the rotor section was terribly clanky and not as fast & smooth as good German or even Czech rotor sets.
After smoothing out the bell creases, I looked over at the rotor section. Oiling both top & bottom bearings as well as the linkage didn't do a whole lot. I finally noticed some 'slop' or 'play' in the ball-&-socket joints as well as the T-joints near the paddles. Oiled those. I had asked him why he had athletic fiber tape around the top screws that hold the stop arms in place. He told me because they kept coming loose! So I took the top screws off, cleaned off the tape and proceeded to take the stop arms off. There was a LOT of 'slop' between where the stop arms and top rotor stems fit together. You could 'wobble' the parts with your fingers. Very loose tolerances; they were fabricated that way. The tuba was only 4-5 years old. The only thing I could then do was use GREASE on those parts and screw them back together. I also used grease on the ball-&-socket joints as there was a lot of 'slop' there too. All of this improved the linkage........a little But you can't really do much when the parts are fabricated with very loose tolerances
One thing I wanna add to this is that when I am doing rotor maintenance on my own M-W CC, I have to make sure the back bearing PLATES are on just right. This is if I actually removed the entire rotor from the casing.
If not, then there is sometimes clanking or the rotor won't move. I have to tap the back plates in alignment "just right" with a plastic/rubber mallet.
The tuba itself actually played very well; nice deep sound, in tune, good response. But the rotor section was terribly clanky and not as fast & smooth as good German or even Czech rotor sets.
After smoothing out the bell creases, I looked over at the rotor section. Oiling both top & bottom bearings as well as the linkage didn't do a whole lot. I finally noticed some 'slop' or 'play' in the ball-&-socket joints as well as the T-joints near the paddles. Oiled those. I had asked him why he had athletic fiber tape around the top screws that hold the stop arms in place. He told me because they kept coming loose! So I took the top screws off, cleaned off the tape and proceeded to take the stop arms off. There was a LOT of 'slop' between where the stop arms and top rotor stems fit together. You could 'wobble' the parts with your fingers. Very loose tolerances; they were fabricated that way. The tuba was only 4-5 years old. The only thing I could then do was use GREASE on those parts and screw them back together. I also used grease on the ball-&-socket joints as there was a lot of 'slop' there too. All of this improved the linkage........a little But you can't really do much when the parts are fabricated with very loose tolerances
One thing I wanna add to this is that when I am doing rotor maintenance on my own M-W CC, I have to make sure the back bearing PLATES are on just right. This is if I actually removed the entire rotor from the casing.
If not, then there is sometimes clanking or the rotor won't move. I have to tap the back plates in alignment "just right" with a plastic/rubber mallet.