Disassemble Rotax

[Lhbone]

Do rotax valves disassemble the same as standard rotors? I am not a tech but was taught how to take apart standard rotors on trombones, tubas, and horns by a very qualified tech. What type of mallet material is best? I only have a softer rubber one currently and suspect I’ll need something more dense.

[harrisonreed]

They are the same, other than how the stop arm grabs the spindle. A rubber mallet should work fine, even though most guides recommend rawhide.

The big difference with the rotax is that the tolerances are very tight, so you need to just take your time with it.

[Lhbone]

They are the same, other than how the stop arm grabs the spindle. A rubber mallet should work fine, even though most guides recommend rawhide.

The big difference with the rotax is that the tolerances are very tight, so you need to just take your time with it.

It's definitely being stubborn...any experience with it not budging? Not sure if I need to let it sit with a penetrating oil before trying again. I see my tech in two weeks, so I may give up rather than accidentally do something stupid.

[harrisonreed]

I've done it a few times but I'm not a tech. Use my advice at your own risk:

Take your punch, put it in the hole, and smack it with the rubber hammer.

Catch the bearing plate with your hand.

[Sesquitone]

It's definitely being stubborn...any experience with it not budging? Not sure if I need to let it sit with a penetrating oil before trying again. I see my tech in two weeks, so I may give up rather than accidentally do something stupid.

Yes, it's supposed to be "stubborn". The end-plate is a (very tight) press fit—designed to keep circularity in the casing. Of course, you have unscrewed the end cap; and removed the toggle arm. By the way, does it have the little Teflon washer (that's helpful when you're reassembling)? Work with something soft (like a big towel) on your workbench (to catch the end-plate when it pops out). A rubber or plastic mallet is OK to use on the end of the spindle. Short sharp chops! You can also just hold a piece of wood over the end of the spindle and hit that with any kind of mallet. The main thing is: no sharp metal tools must touch any part of the valve (except the screw-driver you unscrewed the end-play adjustment bolt with and hex keys for the bumper-stop plate).

More importantly, when you're reassembling, it's critical to get the end-plate seated uniformly all the way around its circumference. For this, you have to gently go round-and-round-and-round with gentle (but firm) little taps until you're sure it's bedded down snugly and evenly all the way round.

And when reassembling, use the end-play adjustment bolt to gently pull the rotor internal flat bearing up onto its mate—i.e. no backlash. Then partially tighten the set-screw on the toggle arm. If the action is "too tight" (i.e. sluggish), unscrew the adjustment bolt a quarter turn and gently tap on top of the bolt. This will relax the tightness just enough without causing end-play backlash. If you over-correct, you can fiddle with it back-and-forth until it's "perfect": free-spinning without backlash (no audible "click" when you try to jiggle the spindle axially). Then firmly tighten the toggle-arm set-screw.

Let me know how you get on or if I can help in any other way, at the following (office) email:

Benny Leonard

[email protected]

[brassmedic]

I think you're going to have a hard time ever getting it out with a rubber mallet. Get a rawhide mallet.

[Lhbone]

It's definitely being stubborn...any experience with it not budging? Not sure if I need to let it sit with a penetrating oil before trying again. I see my tech in two weeks, so I may give up rather than accidentally do something stupid.

Yes, it's supposed to be "stubborn". The end-plate is a (very tight) press fit—designed to keep circularity in the casing. Of course, you have unscrewed the end cap; and removed the toggle arm. By the way, does it have the little Teflon washer (that's helpful when you're reassembling)? Work with something soft (like a big towel) on your workbench (to catch the end-plate when it pops out). A rubber or plastic mallet is OK to use on the end of the spindle. Short sharp chops! You can also just hold a piece of wood over the end of the spindle and hit that with any kind of mallet. The main thing is: no sharp metal tools must touch any part of the valve (except the screw-driver you unscrewed the end-play adjustment bolt with and hex keys for the bumper-stop plate).

More importantly, when you're reassembling, it's critical to get the end-plate seated uniformly all the way around its circumference. For this, you have to gently go round-and-round-and-round with gentle (but firm) little taps until you're sure it's bedded down snugly and evenly all the way round.

And when reassembling, use the end-play adjustment bolt to gently pull the rotor internal flat bearing up onto its mate—i.e. no backlash. Then partially tighten the set-screw on the toggle arm. If the action is "too tight" (i.e. sluggish), unscrew the adjustment bolt a quarter turn and gently tap on top of the bolt. This will relax the tightness just enough without causing end-play backlash. If you over-correct, you can fiddle with it back-and-forth until it's "perfect": free-spinning without backlash (no audible "click" when you try to jiggle the spindle axially). Then firmly tighten the toggle-arm set-screw.

Let me know how you get on or if I can help in any other way, at the following (office) email:

Benny Leonard

[email protected]

First, many thanks for your response - that might be the most detailed instructions I've seen on the forum.

Second, I finally got it out earlier today using a plastic mallet - it took almost no effort in comparison, so that was a lesson learned.

Lastly, I have two more questions regarding Rotax valves. These are on an Edwards B-502i in case that is helpful.

1. There is no indication as to where the rotor sits inside the casing. I'm used to standard rotors where you see the 90 degree angle, but this one has just a single line across. When I have it lined up to on the open side of the horn, I can turn it 180 degrees and have it lined up with Bb again. Are the bore sizes and shape equal on both sides? In theory, I'm thinking yes so it wouldn't matter but just wanted to be sure. It would be a fun April fools joke to rotate someone's rotor 90 degrees so that their horn defaults to the F side of the horn when the lever isn't depressed.

2. Pardon the ignorance, but what is the "end play adjustment bolt"? I'm not seeing anything that would pull the rotor by tightening it. Is this related to how the stop arm attaches to the spindle? Is there supposed to be a gap between the stop arm and the backplate? I noticed before I took the valve apart that the F valve had no space while the Gb has a slight amount. Any guidance on that would be appreciated. I've attached a pic below if that's helpful. Let me know if there's a better angle I should grab.

[Lhbone]

I think you're going to have a hard time ever getting it out with a rubber mallet. Get a rawhide mallet.

Rawhide on order for future purposes - a few taps with a plastic mallet got the job done easily. The rubber was no hope hah. Thanks!

[brassmedic]

I think you're going to have a hard time ever getting it out with a rubber mallet. Get a rawhide mallet.

Rawhide on order for future purposes - a few taps with a plastic mallet got the job done easily. The rubber was no hope hah. Thanks!

Plastic is fine. Just don't use metal.

[Sesquitone]

1. There is no indication as to where the rotor sits inside the casing. I'm used to standard rotors where you see the 90 degree angle, but this one has just a single line across. When I have it lined up to on the open side of the horn, I can turn it 180 degrees and have it lined up with Bb again. Are the bore sizes and shape equal on both sides? In theory, I'm thinking yes so it wouldn't matter but just wanted to be sure. It would be a fun April fools joke to rotate someone's rotor 90 degrees so that their horn defaults to the F side of the horn when the lever isn't depressed.

2. Pardon the ignorance, but what is the "end play adjustment bolt"? I'm not seeing anything that would pull the rotor by tightening it. Is this related to how the stop arm attaches to the spindle? Is there supposed to be a gap between the stop arm and the backplate? I noticed before I took the valve apart that the F valve had no space while the Gb has a slight amount. Any guidance on that would be appreciated. I've attached a pic below if that's helpful. Let me know if there's a better angle I should grab.

In answer to your first question, yes, your intuition is correct, the Rotax rotor is symmetrical and can be inserted so that the single witness mark across the end of the short spindle is in either position, 180º apart, when seated against each of the bumper stops. This is true of most "conventional" rotary valves when the angular throw is 90º. [Let's not think about that April Fools prank turning any rotor 90º!] The first picture below is actually of a CAIDEX valve (which has a "see-through" end-cap—so that the player can check at a glance that everything is aligned precisely; this is critical because of the lipped-tube geometry). But the CAIDEX uses the same casing as (and some other components of) the Rotax.

The second and third pictures show two views of the toggle arm and stops. Once again, this is a CAIDEX (with individually adjustable bumper stops); but the main features are the same as the Rotax. This is a mock-up, with a Phillips-head metric machine bolt (and a steel washer) screwed down into the long spindle, as you can see. The factory Rotax should have a similar machine bolt with a large flat slotted-head (no metal washer needed) threaded into the spindle. This is the "end-play adjustment bolt"—and is a very important part of the Rotax design (and the CAIDEX). If your valves are missing these (and I don't see any sign of them in your picture), take one rotor, while you have it out, to a hardware store and find two (metric) machine bolts with the correct thread and appropriate length—it doesn't have to be too long (but, of course, not overly long so that it bottoms out). You'll also notice the little white plastic washer between the toggle arm and the face of the end-plate (backplate) bearing post. Rotax supplies, from the factory, a little Teflon washer for this—although I suspect that Edwards does not bother to use any washer at this spot. That's a pity because it's part of the end-play adjustment process. Review my instructions for this and they should start to make sense. It's an important adjustment to get the rotor spinning freely but without end-play backlash. There should be no space between the toggle arm and the backplate—ideally filled in with the little Teflon washer (or equivalent plastic washer). [This further helps eliminate any chance of metal-on-metal noise.]

I'm curious as to why you disassembled the valve(s). However, it's always a good idea to clean-up all moving parts while you have them out. When correctly adjusted (see above), because of their precise tolerances, Rotax valves do not need anywhere near as much lubrication as other rotaries (and especially not as much as axial or Hagmann geometries). Just a drop of very light rotor oil placed near the (Teflon) washer—maybe once a week (or less). It will automatically migrate down to where it needs to be. I like the rotor oil supplied by Denis Wick that has some Teflon micro-particles mixed in.

I hope I've covered all your questions. Please keep me updated.




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[brassmedic]

The second and third pictures show two views of the toggle arm and stops. Once again, this is a CAIDEX (with individually adjustable bumper stops); but the main features are the same as the Rotax. This is a mock-up, with a Phillips-head metric machine bolt (and a steel washer) screwed down into the long spindle, as you can see. The factory Rotax should have a similar machine bolt with a large flat slotted-head (no metal washer needed) threaded into the spindle. This is the "end-play adjustment bolt"—and is a very important part of the Rotax design (and the CAIDEX). If your valves are missing these (and I don't see any sign of them in your picture), take one rotor, while you have it out, to a hardware store and find two (metric) machine bolts with the correct thread and appropriate length—it doesn't have to be too long (but, of course, not overly long so that it bottoms out). You'll also notice the little white plastic washer between the toggle arm and the face of the end-plate (backplate) bearing post. Rotax supplies, from the factory, a little Teflon washer for this—although I suspect that Edwards does not bother to use any washer at this spot. That's a pity because it's part of the end-play adjustment process. Review my instructions for this and they should start to make sense. It's an important adjustment to get the rotor spinning freely but without end-play backlash. There should be no space between the toggle arm and the backplate—ideally filled in with the little Teflon washer (or equivalent plastic washer). [This further helps eliminate any chance of metal-on-metal noise.]

That's very interesting. On conventional rotary valves, the end to end play is controlled by the distance between the front bearing and the back bearing, and there is clearance between the stop arm and the bearing. The stop arm serves only to control where the rotation stops. If I am understanding you, with this type of Rotax valve, the end to end play is controlled by sandwiching the bearing between the bearing plate and the stop arm (I'm guessing "toggle arm" is what the rest of us call the stop arm). So does that mean they are manufactured without regard to a precise fitting of the front and back bearings? If Edwards is installing them without a washer, as you suggest, is it possible they don't understand how end play is controlled on these valves? (I certainly didn't.) That seems like a huge problem. Wouldn't that mean the stop arm's squared off bottom surface could be contacting the bearing directly and chewing it up? And aren't most techs who clean the valve and reinstall it likely to install it incorrectly?

[Sesquitone]

That's very interesting. On conventional rotary valves, the end to end play is controlled by the distance between the front bearing and the back bearing, and there is clearance between the stop arm and the bearing. The stop arm serves only to control where the rotation stops. If I am understanding you, with this type of Rotax valve, the end to end play is controlled by sandwiching the bearing between the bearing plate and the stop arm (I'm guessing "toggle arm" is what the rest of us call the stop arm). So does that mean they are manufactured without regard to a precise fitting of the front and back bearings? If Edwards is installing them without a washer, as you suggest, is it possible they don't understand how end play is controlled on these valves? (I certainly didn't.) That seems like a huge problem. Wouldn't that mean the stop arm's squared off bottom surface could be contacting the bearing directly and chewing it up? And aren't most techs who clean the valve and reinstall it likely to install it incorrectly?

Yes, you've identified a potential "problem" of the Rotax axial-travel (end-play) adjustment not being properly understood. The rough sketch, below, is actually of a CAIDEX long spindle—essentially identical to the Rotax, but with some "grooves" cut in to reduce surface friction area (and act as a reservoir for lubricant). The orange colouring shows the thread for the M3 machine bolt that controls the axial travel. Its large flat head sits above the toggle arm (stop arm) and, when tightened, pulls the rotor up until the surface of the flat bearing of the rotor (purple colour) is just in contact with the underside of the top end plate ("back plate"). Hence, no end-play backlash. And, yes, the little Teflon washer supplied by Willson is part of the design—so that there is no (inadvertent) metal-metal contact between the toggle arm and the top of the back plate.

So let me review how to adjust a Rotax (and CAIDEX) valve when reinstalling. Once the rotor is in place, make sure the (Teflon or other suitable) little washer is in place under the toggle arm, which is slightly tightened with its set-screw (enough to hold the spindle in place but let it slide when the adjustment is made). Then the adjustment bolt is inserted and screwed down until the (wide flat) head is just contacting the top of the toggle arm. Gently "jiggle" the toggle arm back-and-forth axially to see if there's any end play. If there's no end play and the rotor spins freely (when "flicked", it should bounce back and forth off the bumper stops), then tighten the set screw firmly, and you're done. If there is axial play—if you can feel it or hear any tiny "clicks"—(with the set screw still only partially tightened), tighten the end-play adjustment bolt to bring the flat bearing of the rotor up into contact with the underside of the back plate. And repeat these steps until you have a free spinning rotor without end-play backlash. If there's any hint of binding, back off the bolt (a quarter turn or less) and gently tap the top of it to relieve the binding. Finally (after the set screw is firmly set), very slightly "over-tighten" the bolt (just enough so that it doesn't work loose over time).

When adjusted this way, the corresponding flat bearing on the other end of the rotor (on the short spindle) is not in contact with the other end plate ("front plate"—according to French horn players?). This "bearing" has no function other than as a "shelf" to knock out the end plate when disassembling. Both spindles are tapered (2% diameter taper), so without this shelf, the bearing would lock up into the end plate in an almost unrecoverable "press fit" if you tried to knock out the end plate (as I can attest to from personal experience when experimenting with no "shelf"!).

I trust this is clear. And I hope that technicians are aware of this important feature of the Rotax (and CAIDEX) designs. Keep track of those little Teflon washers; they get lost quite easily; they become "invisible" on the shop floor.


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[harrisonreed]

That would have been nice to have in a document with the Rotax horns shipped from Edwards.

[ithinknot]

Verschlimmbesserung, as the Germans splendidly term it. A traditional rotor with two tapered spindles and two functioning face bearings requires more work to set correctly at the factory, and slightly more work to adjust when compensating for long-term wear, but it's a fundamentally better design; concentricity is maintained at both ends, and wear is retarded through symmetrical load distribution over larger areas.

If you go down this route, at the very least shouldn't the spindle bearing at the front plate side be cylindrical rather than tapered? As it is, with tapers at both ends, the more the rotor is pulled up against the back plate (i.e. the more end play is taken up), the looser the fit at the front plate gets, creating a vicious circle... compensating for end play reduces the stability of the system overall, accelerating wear in all planes.

[Posaunus]

I feel some new valve design innovation on the horizon!

[Sesquitone]

If you go down this route, at the very least shouldn't the spindle bearing at the front plate side be cylindrical rather than tapered? As it is, with tapers at both ends, the more the rotor is pulled up against the back plate (i.e. the more end play is taken up), the looser the fit at the front plate gets, creating a vicious circle... compensating for end play reduces the stability of the system overall, accelerating wear in all planes.

Not only that, but with the cylindrical short-spindle bearing, you can then eliminate the lower "flat-plate" entirely, thereby reducing mass (and, especially, rotational inertia) even further. For disassembling, the press-fit end-plate (front plate) is knocked out by the lips on the (constant cross-sectional area) rotor tubing, directly. [Note date on accompanying visualisation.] This will, no doubt, appear as "CAIDEX 2.0". It's in the pipeline.

"Great minds think alike", someone once said.


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CAIDEX No lower flat bearing.png

[brassmedic]

What is a "flat plate"?

[ithinknot]

Face, as opposed to spindle, bearing... the bit that's disappeared from the short spindle side in the graphic above.

"Great minds think alike", someone once said.

That was me, too

[Sesquitone]

What is a "flat plate"?

The orange coloured "face" in the visualisation, below. If there were any axial force, it would be a simple thrust bearing. On rotors (where there are no axial forces), if there is no end-play adjustment bolt, the two "faces"—on top (shown) and bottom (not seen here)—act as axial-travel constraints between the insides of the two end plates. With the adjustment bolt, the axial travel is constrained between the (external) bolt head sitting on top of the toggle arm, which rotates in contact (via the littleTeflon washer) with the post on the outside of its end plate, and the (internal) top "face" on the long spindle, that's (just) in contact with the underside of this end-plate. The corresponding "flat plate" on the short spindle is then inactive and can be eliminated (provided the short spindle is not tapered, as explained earlier).


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[Lhbone]

Benny and I are chatting via email now to streamline communication. Will repost here if anything else comes to light in that correspondence.

First, thanks to Benny for all of this info and the illustrations! I think I'm finally understanding how this valve works.

To answer a couple of questions that popped up that I forgot to reply to, in case it helps anyone down the road:

-I disassembled the valve because it completely seized up. I don't know why, but this F valve has always been finicky and has seized up in the past if regular oiling is missed. During the tail end of covid when gigs were few and far between, I left the horn sitting on the stand in my office for about a month, and the F valve completely seized while the Gb was fine. Recently, I knew I wasn't going to be touching the instrument for a bit, so I oiled the valves on all points and put it away in its case. A month later, the F was almost completely seized but the Gb was fine. I was able to manually turn the stop arm with my fingers and tried flooding everything with oil. It loosened slightly but a half bottle in, I felt I needed to take it apart. As soon as I got it apart and re-oiled all surfaces, it was free-spinning and felt great.

-My Edwards did not come with any teflon washers, and I still feel a little confused about reassembly. I now believe I understand Benny's instructions above, but the idea of metal on metal just sounds so wrong.

-I do have the end play bolts with both rotors. See photo attached.

[Sesquitone]

-My Edwards did not come with any teflon washers, and I still feel a little confused about reassembly. I now believe I understand Benny's instructions above, but the idea of metal on metal just sounds so wrong.

From chatting with Christan Griego at the Edwards factory about Rotax valves many years ago, I understood him to say that he did not consider the (Teflon or any other) washers important enough to keep on--even though they would have come along with the Rotax valves from the Willson factory. "Metal-on-metal"--between the toggle arm and the top of the bearing post--is not a problem provided both surfaces are flat and smooth. But there remains the possibility of the toggle arm "catching" on the bumper material (if it's not trimmed down flush with the top of the post). In any case, a thin (plastic) washer between the toggle arm and bearing post is preferable. Teflon, if available. This raises the toggle arm just a bit (to keep it away from any jagged bits of bumper material sticking up); and it helps dampen any hint of metal-on-metal noise.

[brassmedic]

What is a "flat plate"?

The orange coloured "face" in the visualisation, below. If there were any axial force, it would be a simple thrust bearing. On rotors (where there are no axial forces), if there is no end-play adjustment bolt, the two "faces"—on top (shown) and bottom (not seen here)—act as axial-travel constraints between the insides of the two end plates. With the adjustment bolt, the axial travel is constrained between the (external) bolt head sitting on top of the toggle arm, which rotates in contact (via the littleTeflon washer) with the post on the outside of its end plate, and the (internal) top "face" on the long spindle, that's (just) in contact with the underside of this end-plate. The corresponding "flat plate" on the short spindle is then inactive and can be eliminated (provided the short spindle is not tapered, as explained earlier).


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But you said it is tapered, correct? At the risk of repeating an issue that was already brought up: As an engineer, are you concerned about problems with this design? I am not an engineer, but it seems to me that if the front bearing is a loose fit, and given the relatively short length of the back bearing, that the rotor is going to be able to twist in the back bearing, and since the rotational force is applied from a lever that is attached off center and not necessarily in the same plane as the rotation, wouldn't the rotor receive sideways force and end up riding on the inside of the valve casing, and wouldn't this cause it to wear unevenly? The nice thing about the traditional design is that the rotor rides entirely on the 2 bearings, and doesn't actually contact the walls of the casing (or if it does, it will soon hone itself to a more perfect cylindrical shape). Just curious what you thought about that.

[Sesquitone]

But you said it is tapered, correct? At the risk of repeating an issue that was already brought up: As an engineer, are you concerned about problems with this design? I am not an engineer, but it seems to me that if the front bearing is a loose fit, and given the relatively short length of the back bearing, that the rotor is going to be able to twist in the back bearing, and since the rotational force is applied from a lever that is attached off center and not necessarily in the same plane as the rotation, wouldn't the rotor receive sideways force and end up riding on the inside of the valve casing, and wouldn't this cause it to wear unevenly? The nice thing about the traditional design is that the rotor rides entirely on the 2 bearings, and doesn't actually contact the walls of the casing (or if it does, it will soon hone itself to a more perfect cylindrical shape). Just curious what you thought about that.

Yes, you are absolutely correct, in principle. If I were designing the valve from scratch, I would choose the short-spindle bearing to be untapered. However the Rotax evolved from a much earlier design where both spindles were tapered and there was a laborious hand-lapping procedure to bring everything to within very tight tolerances. The 2% diameter tapers meant that, with the amount of wear of the valve over the lifetime of the instrument, the amount of "slack" in the bearings would be almost negligible and not cause any problems. The Rotax is well known for its very tight acoustic seal without mechanical binding. On a less expensive valve with more liberal machining tolerances, this would indeed eventually be a problem. And the CAIDEX has evolved from the Rotax--more-or-less as a "modified Rotax" that uses many of the same parts. The "inertia" in the system in this case is in the production line. Ultimately, we will get to the untapered short-spindle bearing.

[brassmedic]

But you said it is tapered, correct? At the risk of repeating an issue that was already brought up: As an engineer, are you concerned about problems with this design? I am not an engineer, but it seems to me that if the front bearing is a loose fit, and given the relatively short length of the back bearing, that the rotor is going to be able to twist in the back bearing, and since the rotational force is applied from a lever that is attached off center and not necessarily in the same plane as the rotation, wouldn't the rotor receive sideways force and end up riding on the inside of the valve casing, and wouldn't this cause it to wear unevenly? The nice thing about the traditional design is that the rotor rides entirely on the 2 bearings, and doesn't actually contact the walls of the casing (or if it does, it will soon hone itself to a more perfect cylindrical shape). Just curious what you thought about that.

Yes, you are absolutely correct, in principle. If I were designing the valve from scratch, I would choose the short-spindle bearing to be untapered. However the Rotax evolved from a much earlier design where both spindles were tapered and there was a laborious hand-lapping procedure to bring everything into very tight tolerances. The 2% diameter tapers meant that, with the amount of wear of the valve over the lifetime of the instrument, the amount of "slack" in the bearings would be almost negligible and not cause any problems. The Rotax is well known for its very tight acoustic seal without mechanical binding. On a less expensive valve with more liberal machining tolerances, this would indeed eventually be a problem. And the CAIDEX has evolved from the Rotax--more-or-less as a "modified Rotax" that uses many of the same parts. The "inertia" in the system in this case is in the production line. Ultimately, we will get to the untapered short-spindle bearing.

Thanks for the info.