| Greg --
Yes, and no.
First thing to do with any horn with problematic valves is clean the horn internally with mild detergent-type cleaners (I won't get into which are the "best" ones ...).
Generally, there will be something "out-of-whack" with either the valve piston or the valve casing. In this case, a professional tech will know what to do (he will have specific-sized mandrels for the horn to effect this procedure, and sight along a leveling block to straighten the piston).
Ususally, some force or shock to the horn (such as "knocking" it into something, dropping it, bumping it, etc.) will transfer a stress to the valve casing &/or associated "knuckle", causing a "bind", or "torquing".
Again, and I can't stress this enough -- "lapping" removes metal.
Don't think that "hand-lapped pistons" as you see advertised is so wonderful, and so "hand-made in America", or some-such. The last thing you want to do (when all else fails) is remove metal. When it is gone, it is gone.
Much of the problems in this area (and just about any subject area), is we are looking for a "quick fix", or "magic pill", or "magic bullet". Screw that !! Remember the slogan about "the old-fashioned way" ?
Proceed at your own (or the horn's) peril ....
Robert Rowe |