- - Please visit: Wichita Band Instrument Co. - -
K asks, “Why do valves clank and what can be done about them?’
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Dave replies: Valves clank because something is loose.
The loose parts are given momentum when the valve lever is depressed or let go, and when the motion is stopped, “Clank!”, the loose parts hit each other and make noise.The first test is whether the rotor is loose in the casing. I grasp the rotor by the bottom bearing (the long shaft attached to the rotor stop) and push and pull it into and back out of the casing.
If it’s loose, there will be motion (end play) and I’ll hear clicking. Then I pull the rotor straight out toward the bottom bearing and move it side-to-side, testing for play in the bottom bearing.
Taking the end play and side-to-side play out of the valve is a technical procedure and I do not recommend doing it unless one is trained. End play is taken out by modification of the top bearing plate or sometimes the casing, so that the bearing plate fits further down on the rotor. Side-to-side play is taken out with a device known as a collet, or leaf, swedger.
This device closes the bottom bushing down onto the rotor shaft. If either adjustment is too tight, then proper tolerance is restored with an ultra-fine lapping compound. There should be just enough space in the bearings to allow a bearing oil to lubricate the rotor but allow it to rotate freely.
Other loose parts can cause noise, too. The rotor stop must sit snugly on the rotor shaft, all the screws must be tightened down, the strike plate that holds the bumpers should be held on tightly, the bumpers should be in good condition so that the rotor stop does not hit the strike plate, and mechanical linkages should be tightened to the point where parts have just enough tolerance to move freely with proper lubrication. One of the most often overlooked sources of clanking noise is a loose rotor stop, so be sure your technician checks that.
A well-fit rotor with no loose auxiliary parts will rotate quickly and freely, will not hang up at all, and will be almost silent except for the slightest sound when the bumper is struck.
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