Posted by Joe S. on March 04, 2000 at 21:10:17:
A band director here in Memphis has one of the old "plastic-filled rotors" HB 4/4 rotary tubas. Just like many of these, his rotors were sticking, once the instrument warmed up - very annoying. Mr. Hirsbrunner has offered his solution often which involves very hot temperatures and removal of additional material from the rotors. (Sorry, but it seems to me that close tolerances are JUST as important as free operation.)
I have never been willing to mess with this Hirsbrunner-recommended procedure, due to the fragile appearance (bronze rotor shell appears to be supported by little "sticks" of metal, which extend through the plastic filler) and my unwillingless to be liable for a destroyed rotor on a very expensive instrument (which I didn't sell, in the first place).
Since I have observed that "good ol'" BLUE JUICE valve oil often seems to "forgive many sins" on all types of valves, I recommended that he try it on those rotors. Since then, every time I have seen him at regional band events, he has bragged to me about the apparent disappearance of his long-standing problems.
Perhaps those of you with these old plastic-filled HB rotors might at least "try" BLUE JUICE before resorting to more rash solutions.
no guarantees...
-Joe