Posted by The Unknown Repair-dude on November 30, 1999 at 21:38:15:
In Reply to: Re: Bottom valve cap posted by Dave on November 30, 1999 at 21:08:32:
If it is a Yamaha, be particularly careful, because the "fit" of the casing interior goes all the way to the bottom of the threads and there is no "relief" area under the casing threads ("cheeeeeap").
If it is an American make, you can be a tiny bit more "determined". Most American tubas have thicker-walled casings, too, besides that nice "relief" area at the bottom interior of their casings.
Medium blows around the sides of the cap with a medium size rawhide mallet will probably dislodge it. Otherwise, if, against my advice, you do the old (AAHHHHH !!!) "pliers" thing, do NOT let the jaws touch ANYthing but the stuck cap (NOT the casing! - You could dig grooves into the casing that would transfer to the inside and make the piston hang up!) and do NOT allow the pliers to slip and grind on the cap. If you DO use pliers (I don't advise it.) I don't recommend putting a rag over it to protect the cap, because the "trade off" is that you cannot see what you are doing.
Sure, you can spray some penetrating oil in there (That new-ish brand with the brown and yellow label is pretty good stuff.), but the cap will still be tight, even after the penetrating oil has soaked in. (I DO recommend using penetrating oil first and letting it soak for a while.)