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I recently picked up a used Cerveny 686-4MR BBb for a "very" good price. It plays great but could probably use a good going over by a tech in the near future but my immediate question concerns the 3rd and 4th valves. Both valves protrude ever so slightly out the back of the valve casing...a tiny fraction of an inch. This is noticable when the rear valve caps are removed for applying bearing oil. It is also noticable in that the rear valve caps do not screw "flush" to the casing as they do on valves 1 and 2. Why is this? Can it be fixed by me (I am extremely non-technical) or should it be addressed by a qualified repair person? Will it do any damage to play as is until I get it to the city in the next few weeks?

Also, as I am new to rotary maintainence...what is the best way to oil the bearings? I am not talking so much about the procedure...I found plenty about that by searching the archives...but rather, how do set the horn so you can access the back without damaging the valves and linkage? I know that many of you post collective groans when you see a photo of a horn horn placed on its valves to show the back (for ebay or whatever), but how else can you safely place the horn so that this procedure can be done?

Thanks in advance for your help!

It almost sounds as if the rotors in question aren't original equipment. I wouldn't try to fix this one yourself--take it to someone who knows what s/he's doing. If you're nervous about cost, see if you can have the horn looked at before you plunk your hard-earned bucks down.

kegmcnabb wrote:Both valves protrude ever so slightly out the back of the valve casing...a tiny fraction of an inch.

Assuming that you are saying that the rear bearing plate sticks out past the rotor housing....

I really think you should take your horn to a qualified technician. Secondly, most rotary horns I've seen are not balanced well enough to stand them on the bell to perform work. Any time I put a tuba on the bench on the bell, I also tie the bottom bow to a hook in the ceiling.

I know there is some risk here since you don't have any experience with rotor maintenance, but here goes:

If the rotor has axial play (front to rear), the rear bearing plates might not be firmly seated in the rotor housing. Push and pull on the stop arm with your fingers. If the rotor moves much more that just a couple of thousanths of an inch, the bearing caps are probably not seated. This is pretty common when someone puts a rotor back together without knowing what they are doing. With the back cap screwed on, use a light rawhide or plastic mallet to tap the center of the rotor cap. If the cap can then be screwed on a little futher, and the rotor does not get tight... then the bearing plate was probably not firmly in place. Keep tapping and screwing the cap on until the cap bottoms out on the casing. If the rotor still turns free, you've done a good job. If the rotor gets tight, loosen the cap a bit and tap the top of the stop arm. The rotor should loosen up again.

As one poster already mentioned, there is a chance the problem is the result of parts being swapped into the horn without properly making the required adjustments. If there is no end play in the rotors, and they are working OK, ... then you should just leave them alone. Remember that my first comment was to take the horn to a qualified technician.

SpartanContra wrote:When i had that (model) horn, I would oil it with the horn in my lap, with the valve buttons down, but between my legs. i worked for me

That's how I oil my Cerveny 683 - with one more detail - the bell goes out, the tubes toward me. The bell stack is lots less dense than the rest of the horn, so putting it on my lap away from me helps keep the horn from jumping off on the floor!

SpartanContra wrote:Just out of curiosity, where did you pick this up?

Green Bay...which really seems to have a lot of tubas floating about.

Hey everybody, thanks for the advice. I think a trip to the city and a qualified repair person is the way to go.

kegmcnabb wrote:Also, as I am new to rotary maintainence...what is the best way to oil the bearings? I am not talking so much about the procedure...I found plenty about that by searching the archives...but rather, how do set the horn so you can access the back without damaging the valves and linkage?

I oil the back bearings by rest the tuba bell on a big well padded arm chair and then lay the bottom bow on a padded foot stool, so the tuba is resting between the two with no pressure placed on the valve linkage.

That way I can comfortably unscrew and oil the rear bearings while sitting in another chair.

The once I tried oiling with the tuba on my lap, my fly zip caused a small scratch on the back bow, so never again!

lay down, valve levers down, put something like a soft CD Wallet where the main tuning slide is to rest it on