Valve guide question

[csherman]

Hey all!

My valves have been feeling pretty funky lately. There's no gunk on them and there's certainly lack of oil, so could the valve guides be an issue? I heard if they were worn down, they'll start to twist. I had my valves vented recently, which includes chemical cleaning, so I'm sure they're not dirty or have a petroleum build-up. How often do you piston junkies out there have to replace your valve guides?

Best,
csherman

[sousaphone68]

Hello I am not a repair tech but I have played one of my piston tubas for 25 years on the original brass guides.
The guides are worn and they make the valve action noisy but not slower.
If the guide was twisting on yours you would know very quickly as it would have to be loose to the touch.
Other than dirt slowing my valves I have found that as the springs age sometimes the top coil curls under the second coil and the valve feels very strange when used.
I would if it is only the one valve that feels funky swop the springs around and see if the problem travels.

[Roger Lewis]

It would help to know the brand and model of the horn. Also if it started after having the valves vented I would suspect that there may be some sight burrs where the holes were drilled.

Roger

[dwerden]

The valve guides should be perfectly parallel with the valve itself. If they seem to have turned slightly you'll have valve action problems. So as said above, that is the first thing to check.

Also, check the slot that the guide travels in. Us a toothpick to clean it down in the "corners" where a cloth might not scrub. Depending on use and even the oil you apply, some residue can build up there.

And with many piston valves, the bottom cap must be clean. Any gunk that settles in there will find its way up and muck things up for you. Chemical cleaning probably would not fix that unless the technician was diligent and took it apart for some manual cleaning.

If the guides are not metal (or even if they are, in some extreme cases, contact with the top of the valve casing during reassembly can eventually cause the bottom of the guide to "mushroom" out a bit so it no longer cleanly clears the slot. If this has happened, you might be able to trim off the excess with a razor blade until you can have new ones fitted.

[csherman]

Thanks for the troubleshooting tips, everyone! To answer a few questions...

This is a PT6P, and the valves were still feeling weird before the surgery ( I figured that the chem cleaning would help clear some of that funk out).
Do you all recommend brass valve guides? I don't have a lot of experience with them. It seems like they would be much more durable, but really noisy. Maybe I'm wrong?

Thanks all.

[dwerden]

Oh, I REALLY prefer plastic guides! Brass guides are indeed durable, but they are also noisy. I have not had trouble with plastic guides. My Besson EEb from the early-mid 1980's still has the original guides. They are looking yellow and should probably be replaced, but in any case they have just kept working. The plastic guides on my Besson and Sterling euphoniums have also been fine. And I'm sure the ones on my Adams will be just as good.

But I treat them with reasonable care. I DO try not to let them slam into the top of the casing when reassembling after cleaning or oiling, which helps. Otherwise, I don't give them a second thought.

[Dan Schultz]

I don't have any problems with either brass or plastic guides on any of my tubas.

The key here (excuse the pun) is the condition of the slot. The slot MUST be smooth and straight for any guide to work well. It also needs to have sufficient depth for good guide contact.

When pistons are overhauled... the depth of the guide slot is diminished by however much material is removed from the casing to clean up the bore. I've seen many problem caused because the guides might then be reduced to 'slivers' that tend to wear quickly and ride up on the edge of the slot.

Properly fitted guides should have square, sharp corners and extend as far into the slot as possible.