How to replace screw-in guides

[coolguy684]

So I replaced the old brass tacquets with nylon ones on my BE 960. Problem is that I know that someday, the nylon will wear and even now, it's pretty impossible to get a good hold of it to get the screw out to replace it. What's the solution to nylon guides that can't be gripped by vise-grips or pliars?

On a side note...I'm thinking eventually it'd be nice to have the stainless pistons machined to accept the modern Besson guides. Can repair techs machine the tops of pistons to do this kind of job though?

[ghmerrill]

So I replaced the old brass tacquets with nylon ones on my BE 960. Problem is that I know that someday, the nylon will wear and even now, it's pretty impossible to get a good hold of it to get the screw out to replace it. What's the solution to nylon guides that can't be gripped by vise-grips or pliars?

On a side note...I'm thinking eventually it'd be nice to have the stainless pistons machined to accept the modern Besson guides. Can repair techs machine the tops of pistons to do this kind of job though?

I suggest you email Dan Schultz (thevillagetinker.com) and ask him. I'm sure he'll be happy to provide this info.

[bbocaner]

drill them out.

I doubt a 960 has stainless pistons. Probably monel or nickel silver. Yes, you could probably drill holes in the top of the piston to accept the modern style valve guides. There will be some work to change the length of the stems, felts, etc. to make it all work out, though. Probably more trouble than it's worth.

[ghmerrill]

I tend to agree that the changes are more trouble than they're worth -- and I'm not sure that retrofitting the guides would yield all that much benefit. I've seen people say that they've retrofit the newer valve guides to old horns, but as bbobocaner points out, it's not as easy as just drilling an index hole and putting the valve guide on.

In terms of drilling out the old guides, you need to take care with this. The danger is pushing any of the material (whether brass or plastic) into the hollow piston. Dan's recommendation to me for brass guides is to absolutely use a left-hand drill (in a drill press) since (a) that may actually back out the guide all by itself, and (b) if it doesn't, at last you don't face the danger of actually driving the guide into the piston.

I might try a couple of things first, like

1. Cut a slot into the guide head so you can use a flat blade screwdriver to back it out.
2. Superglue (if that will work on that plastic) a little bolt or dowel to it so you can grab that with pliers and back the whole thing out.
3. Maybe try a very small ez-out (screw extractor) on it (which is close to using a left-hand drill). If I were to do this, I'd put the piston in a machine vise on the drill press, chuck the ez-out, and then BY HAND turn the chuck.

I've seen some people suggest melting them out. But I've also seen people who tried that say that it's a real mess and not all that easy to get it right. Persnoally, I'd avoid that approach.


But very likely the first thing I'd do is ask Dan .

[daruby]

I am not even sure that the older 960 or early Globe Stamp 967 with metal guides had valves the same length as the later ones with plastic guides. The later valves have to account for the width of the guide on top of the piston as well as the felts. The earlier valves have had a cork and felt combo that accounted for a similar spacing, but again I am not sure this distance from valve cap to the top of the valve is the same. The slot for the guide tab to recess in the top of the piston would have to be machined and you'd need more modern stepped valve stems to hold the guides in place. I wouldn't bother (or even attempt this). I'd just stick with good screw in plastic guides. If you want longevity, go back to metal. If you want quiet, then just drill out the nylon screw-ins.

[daniel76309]

In terms of drilling out the old guides, you need to take care with this. The danger is pushing any of the material (whether brass or plastic) into the hollow piston. Dan's recommendation to me for brass guides is to absolutely use a left-hand drill (in a drill press) since (a) that may actually back out the guide all by itself, and (b) if it doesn't, at last you don't face the danger of actually driving the guide into the piston.

I'm a little curious as to what is the danger of introducing nylon bits into the piston. Are you thinking they would find their way out at some point and make the valve stick?

[ghmerrill]

I take it that you're thinking that since the nylon bits wouldn't make any noise, then they wouldn't present a problem. But this still hardly seems a "best practice". I doubt that they would find they're ways out and cause sticking valves -- in fact, I see this failure to find their ways out to be just the problem. What I'd be most concerned about stems from the fact that the interior of the piston is hollow and has drain holes at the top and the bottom so that water accumulating in it (as the piston is used) can drain out (and ultimately onto you're lap, making a mess of your pants -- this is a "design feature").

So now you've got bits of plastic in there (and perhaps more each time you replace the guides). The plastic will be pretty good at attracting gunk to its surface and sticking to it, probably creating little "gunkballs" over time. Plastic in general is also quite good at harboring bacteria. So mostly I'm thinking about bacteria-laden gunkballs that can't be cleared out of the piston and that could in addition block the bottom drain hole of the piston.

This is not a situation I would like to see develop in one of my instruments.

[jennyt125]

Been using the nylon valve guides Chris mentions rather than the metal ones in the UK for years and never had any issues.
We usually tap out the valve guide hole to a larger size to accept the Wilson nylon ones which are pretty tough.
Even the modern 'sit on top' valves guides can shear off pieces of plastic a well known problem when some Besson quality was poor and they weren't machining valve guide slots cleanly.
I have had one of my Imperial EEb tubas fitted with the modern valve guides which sit on top. Nothing fancy they were just drilled out to sit on top so probably a slight alignment issue but being a tuba it is not too critical but I wouldn't bother having it done again.

[daniel76309]

Thanks, that makes sense. I wonder if one could use compressed air to create and sustain "positive pressure" inside the piston while drilling. That way any bits of nylon would blow out rather than falling in.

[ghmerrill]

I'm having visions here of things like a very small air compressor in the piston. Or some Rube Goldberg contraption hooking a compressor to the piston bottom to create the positive pressure. And then perhaps an exploding piston when the pressure goes too high. I will leave that experimentation to others.

The fact remains that repair techs replace plastic valve guides all the time, and without a lot of drama. It can't be that difficult.

By the way, there seems to be a lot of discussion on various trumpet forums about the desirability of plastic vs. metal valve guides -- with a number of claims that Kanstul decided to abandon plastic guides in favor of metal. A number of people seem to favor metal guides for several reasons. The usual reason that plastic is preferred is that they are much quieter than metal ones. They are also much easier to fit and trim. However, a well-fitted metal guide should not be noisy. Virtually all of the noise from metal guides comes from the side-to-side movement that occurs when they get worn. You might think that there is some noise from the guide bottoming out at the end of the piston stroke, but this doesn't seem to be the case (given that you have correct felts and alignment) -- and note that the contemporary Yamaha-style "plastic" guides have a metal tab exposed on the bottom of the plastic portion in the channel.

I have both plastic guides and metal guides to install in my old Buescher horn -- which I still haven't managed to get around to doing. As time goes on, I'm leaning more towards meal.

[bbocaner]

Frankly, Kanstul valves are terrible, and I wouldn't take their clinging to antique manufacturing methods as proof of one method being better than another. Pretty much everyone else is using some sort of plastic valve guide.

I would think that running some water through a piston at any pressure, from the top vent down to the bottom vent, would be more than enough to flush out any pieces that migrate in there.

[ghmerrill]

Frankly, Kanstul valves are terrible, and I wouldn't take their clinging to antique manufacturing methods as proof of one method being better than another. Pretty much everyone else is using some sort of plastic valve guide.

True. But do recall that those "plastic" valve guides (at least the ones I've seen) have a metal base and tab that rides in the guide channel. I'm not sure it's quite fair to characterize metal valve guides as "antique", though I do suspect that one of the reasons for going to the more "modern" approach is the ease of replacement. I THINK the Jupiter ones (as opposed to the Yamaha) do NOT use the metal base. But I haven't been able to put my hands on a set yet. I'll also concede that if I had to choose between two horns that were identical except for the valve guides, I'd choose the "modern" one.

I would think that running some water through a piston at any pressure, from the top vent down to the bottom vent, would be more than enough to flush out any pieces that migrate in there.

Color me skeptical here -- given the way that plastic shaves off into strips and curlicues. You may be right. Just not a chance I'd be willing to take without insight from people who've actually done it with some frequency. However, I also think that in general you shouldn't face the problem and should be able to get the plastic guide out.

[bbocaner]

Besson guides are solid plastic. Or delrin, or whatever they are actually made of. They SHOULD last on the order of dozens of years without needing replacement. I know I have replaced one sooner because of a weird reaction with a particular brand of valve oil that softened the plastic, but on most of my other instruments this just isn't a part that wears significantly.

[tonewheeler]

a number of claims that Kanstul decided to abandon plastic guides in favor of metal. A number of people seem to favor metal guides for several reasons. The usual reason that plastic is preferred is that they are much quieter than metal ones. .

When I was looking into buying a new horn almost 3 years ago. I tried the Kanstul line, but their noisy valves were a deal breaker. It's a shame because their factory is in Anaheim, CA, in driving distance from me. I went to their factory last year while my friend was having his Miraphone tuba worked on. They provided outstanding customer service and repair work. I also had the opportunity to try out a couple of their euphs from the showroom. Again, unbelievably noisy and clanky valves, all mainly due to the metal valve guides. Totally unacceptable in my book.