Valve stem loose

[lost]

My old buescher 690 has a loose valve stem. The screw port seems to have lost metal or something, now there is a lot play. The stem and button almost popped out today during a parade. I have been screwing it in with a piece of tape attached avoiding going to a repair shop, since there are few around Boston. Is this an easy fix to do it the right way? Note I was tempted to get some epoxy and mash it in but decided not to....thanks for any info.

[Sousaswag]

I had a similar problem with my big Holton. My repair guy made a new set of stems for it.

I believe to fix it right you may need to re-tap the hole in the case that it’s damaged. Whatever thread size the tap is, the new stems will be.

Regardless, it wasn’t expensive. I’d recommend having it done right.

[lost]

Whats a retap?

[arpthark]

I'm thinking old Buescher valve stems were soldered into the piston? Trying to remember if mine was...

[lost]

They have been screwed in but it is very shallow.

[bloke]

So many piston tops are LEAD soldered on that it's a tricky'delicate proposition to "restore" a piston to it's original (female) stem threads.

As an example, I've found that many of the plated Yamaha pistons are completely lead soldered (no brazing) together...even their porting tubes

...so it would be easy to ruin a piston by drilling out the center, brazing in a cylindrical chunk and re-drilling/re-tapping, as the brazing could cause a lead-soldered piston to fall apart.

If no lathe and no brass stock...(ie. a repair via minimal tools/resources), I might (??) suggest this:

Determine whether the stem (via testing other stems), or the female pistons threads, or BOTH are worn.

If the female piston threads are worn (and - again - MINIMAL resources) I might (?? note: question marks)

- tap the female threads out to the next size (no larger than necessary for good threading, and - preferrably - a common size)

- buy (hardware store or McMaster or wherever) a short brass screw of the new thread size

- alter it as shown in the picture (nice flat 90%/square, thin top, which will rest on top of the piston - KING tuba/sousaphone stems are factory-made with a shoulder, and they break/wear the LEAST of any)

- silver braze the altered screw to the bottom of the original valve stem (after everything has been nicely/squarely cut off the bottom of the valve stem beyond the smooth cylindrical part - making every effort to braze it on 180 degrees/colinear

- install the altered stem, and install a top-of-piston felt that is X amount thinner (the thickness of the remaining screw head, and hopefully that ground-down top is quite thin - such as .5mm) than the other felts

This isn't a restoration, but it's a "good" repair, (again) for a shop with very few tools/resources.


ALTERNATELY (with at least a lathe - or being a good enough eyeballer to drill perfectly in the center at at a perfect angle), the worn female threads could be drilled out, a round slug could be LEAD soldered (not brazed) in, and the center could be re-drilled and tapped to the ORIGINAL threads, but this assumes that the MALE stem threads are NOT worn, or that an oem MALE stem replacement is available.

Beyond this, there are even better options (more tools/more skills/etc.)

brass bolt altered.png (92.92 KiB) Viewed 1077 times