Piston Grabbing

[Tuba Guy Dave]

Hello all,

I have a bit of a dilemma. I'm having issues with the 1st piston on a King 2341 (new style). When I press down the piston and release, it will occasionally grab about 3/4 of the way back up. This occurrence is fairly inconsistent. I've tried valve oil, and it doesn't seem to be working. I've checked the valves to see if there is anything causing it to grab, but everything seems to fine. This is a school owned instrument that seems pretty beaten, so could it be from general misuse? Also, it hasn't been played on for several months after it was cleaned, and only has been played on for a week or two now. Being a high school student, I am limited in my knowledge of tuba repair. Are there any general issues that anyone has knowledge of?

[Dan Schultz]

Several problems come to mind:

1) As others have mentioned... check the valve guides and slots. Also take off the fingerbutton and view the position of the stem as it passed through the hole in the valve cap. Could just be a bent stem.
2) The piston may be bent. Try other pistons in the #1 casing.
3) The ports on the #1 casing may be distorted due to pressure on the valve circuit of leadpipe. Try the #1 piston in the other casings. Try exerting a little pressure 'here and there' on the 1st tubing circuit and see if the problem gets better or worse.

If #2... you might get by with gently lapping the piston.

If #3... you probably need to seek the help of a qualified repairman. This can be fixed.... sometimes just by applying enough heat to allow a solder joint to 'relax'. But isn't something a non-professional should mess with.

[PDCIITuba]

It could just be that the valve needs to be relapped with a very light lapping compound. I just encountered this problem cleaning out a customers tuba, I lapped all four valves, cleaned them out, oiled them up and they worked great if not better than before.


personal background: I make all of the piston valves for S. E. Shires Co.

[Tuba Guy Dave]

Thanks for the quick and plentiful responses!

While playing earlier today I realized it tended the get stuck whenever I would pressed closer to the edge of the piston.

I just checked to see if the stem of the piston was bent. Slightly bent, but not any different in relation to the other pistons.

I checked the valve guide, it is slightly rougher feeling than the others, but otherwise not much noticeable difference.

Finally, I switched the piston with that of the 2nd, and both work without any issues. Should I get it checked out still, or will this be a viable solution? If the problem rears its head again I'll most definitely take it to a repairman.

[Tuba Guy Dave]

...possibly either from it being installed under tension, or from someone carrying the tuba around by holding on to the mouthpipe tube.

That is very probable considering it was lent to a middle school the previous year. Very low chance of it being handled properly.

[Donn]

As the #1 piston works well in the #2 casing

But - am I right? - the #2 piston works well in the #1 casing?

I had this problem occasionally with my sousaphone for quite a while, before it occurred to me that the piston wasn't really all that well lubricated. I've always just dropped some oil in at the top and assumed it would work its way down pretty well on its own, but it seemed that with this one, I need to pull it most of the way out and make sure there's oil all over it.

Another easy thing to check -- gunk coming from the ports can hang the piston up.

[jorgeskid]

I played one of these for a while back in high school. I had the same problem, but it had to do with where my fingers were on the valve caps. Since they are so large, it seems like if you don't press right in the center, the valve rubs a bit...

[Tuba Guy Dave]

I played one of these for a while back in high school. I had the same problem, but it had to do with where my fingers were on the valve caps.

That seems to be where the issue occurs. I stopped by a local Music and Arts store and the guy cleaned out the casing as well as realigned the slightly bent valve stem. Upon exercising the piston it felt a lot smoother. We will see the results in practice tomorrow!

Edit: Played the horn today, worked great! Problem solved! Cause due to either gunky valves or bent piston stem.