a question for the repair guys

Discussion in 'Trumpet Repair and Modification' started by mike ansberry, Oct 29, 2013.

  1. mike ansberry

    mike ansberry Forte User

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    I had a college kid bring a relatively new Jupiter sousaphone to my shop last night. The #3 piston was bunged up a little on the bottom 1/3 and it was not working. I trued it and lapped it lightly and it worked very smoothly. Until you tighten the bottom cap. Then it sticks. I haven't seen this problem before. Any ideas what causes that and how to fix it?
     
  2. Vulgano Brother

    Vulgano Brother Moderator Staff Member

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    While waiting for the wise ones to respond, just a quick question--do you get the same result when you screw the 2nd or 1st valve cap on the third valve?
     
  3. A.N.A. Mendez

    A.N.A. Mendez Utimate User

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    Bottom of the tube is slightly out of round. Need a valve tube mandrel of the correct size....
     
  4. mike ansberry

    mike ansberry Forte User

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    The second, third, and fourth valves work fine in the 3rd casing. The 3rd valve did not work in the other casings.
     
  5. A.N.A. Mendez

    A.N.A. Mendez Utimate User

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    Valve is slightly out of round, need valve mandrel of correct size......[​IMG]
     
  6. stumac

    stumac Fortissimo User

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    I would think you need a little more work on the bottom of the valve, can you check it on a surface plate or a piece of plate glass, there may still be a little distortion of the valve. You might need to do a light lap with the cap tightened.

    Regards, Stuart.
     
  7. Brekelefuw

    Brekelefuw Fortissimo User

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    Take a dent ball and lightly tap it in the bottom of the casing. Don't go too far or you are in for a major headache.
     
  8. musicalmason

    musicalmason Forte User

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    Is the bottom cap very tight going on? Sometimes if there is plating left in the threads of the cap, it will still thread on, but rather tightly, this puts pressure on the casing. You can try working a little bit of lapping compound on the threads of the cap, but just a littl bit, it won't take much. If that doesn't do it, just keep working that valve in th casing (if you don't have a Sousa valve mandrel...most don't). Good news is, if you ar just working the bottom of the valve, and are careful how you do it, there is almost no chance of causing a leak. No air moves near the bottom of the casing, it is just a bearing surface.
     

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