Re: Re: Rotor Noises

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Posted by C(G) on December 29, 2003 at 12:50:04:

In Reply to: Re: Rotor Noises posted by Allen on December 29, 2003 at 12:04:29:

The first thing to do is to determine what's causing the noise, the rotor or the linkage. First valves get substantially more use than the other ones, so they're the first to show wear (they also get more of the crud you blow down the leadpipe).

Unscrew the back valve cap and make sure that the back bearing plates (under the caps) on the rotors are seated home correctly--there should be no visible space between the edge lip on the bearing and the valve casing. Screw the back cap on finger-tight--a little oil on the threads will make it easier to remove next time.

Grasp the rotor stop-arm and try wiggling it up and down and from side to side. If there's substantially more free play (and noise) with the first valve than with the others, you've got ordinary rotor/bearing wear. If the rotor seems okay, hold the stop arm still with one hand and wiggle the key (spatula) for that valve. If there is more play with the first valve doing this than with the others, you have linkage wear.

If you've got a Miraphone tuba, a temporary solution to rotor/bearing wear is to turn the adjusting screw in the bottom cap slightly clockwise until the noise just stops. For a permanent solution, continue reading.

Other brands of tuba will require either the insertion of a brass shim washer between the rotor and the bearing plate, or some material removed (on a lathe, as Joe S. mentions) from the bearing plate to take up the slop. Side-to-side noises may require that the bearing be "swedged" (shrunk) slightly to take up the side-to-side wear. Either is an operation best left to a repair tech.

Linkage wear solutions depend on the type of linkage you have. If you've got the "S-arm" type popular before about 1970, it may mean only that some surfaces have worn and that they need to be refurbished. Leave it to your repair tech.

If you have a ball-and-socket type linkage, inspect the the assembly for cracked plastic sockets--the early Miraphones suffer from nylon parts getting brittle and cracking. If this is the case, have your repair guy order and install new parts.

If there isn't any breakage and the ball part just seems to fit sloppily in the socket part, a little heavy grease or oil in the socket can quiet things down substantially. Just another stopgap--the permanent solution is to replace the worn parts.

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