Scooping out rotor core - What can possibly go wrong?

[sirisobhakya]

I recently tried the Yamaha YBL-835 and like it, especially the larger sound and more open feeling. I don’t have or earn that much money to burn for a second new horn, though.

Seeing from the part list that the 835 only differs from my 830 in just a few aspects: gold brass tuning slide (which I have already), new leadpipe, bored-out no-step gooseneck (which should be very small difference), brass rotor caps, and scooped out rotor cores (the port is now U-shape instead of ʊ-shape), I have been toying with the idea about changing the rotor cores. However, Yamaha would not sell only the core, rather the full rotor assembly at almost $600 each. The potentially cheaper, but much more destructive way, is therefore cutting the rotor cores of the 830 into the desired shape.

I understand that there is no turning back, and if the result turns awry, I have to buy the rotor assemblies to fix it, sacrificing $1,200 plus labor cost.

Therefore I would like to ask: what can possibly go wrong with this modification? I understand that the response would change, probably drastically, but how about the intonation? And the change in the sound, would it be larger as I hope? Assuming that it is done by a competent tech, would there potentially be more friction/sticking problem? Overall, is it worth the risk? Or should I just do more OT and save up for the real deal?

[ithinknot]

Bad idea on a modern horn with fundamentally good valves. The difference is unlikely to be as "drastic" as you imagine, and you can't know which of the changes between the 830 and 835 had the effect you like (...and then there's sample variation...).

All you know is that you liked the 835 as a whole, so sell your 830 and buy one.

[Burgerbob]

Just get a new horn.

[hyperbolica]

The upside seems non-existant or small, and potential downside could leave you without a horn and wind up costing a lot of money . I'd let it be, and switch horns eventually if you still think its worth the money.

[tbonesullivan]

The valve caps on the 835 are also brass, which can change things compared to the standard nickel silver or aluminum Yamaha used later. The casing and knuckles are identical, so part of me really questions how much more "open" the valves are, and removing the "lip" on the edges of the valve cores also means that the air passage on the inside of the valve is now D-shaped, instead of oval.

Another thing to consider: when is the last time you had your entire horn chemically cleaned? Mineral deposits and oxides develop over time on the interior of most of the tubing on the bell section, which can have some effect on how it resonates. You were comparing your daily driver, which would definitely have some oxidation, along with pretty much brand new horns.

Then you also have "new horn" effect, which definitely is real.

Honestly, I would agree with the others that you should either leave your horn as is, or trade it in for an 835.

[harrisonreed]

Or get an Edwards

The new Yamaha basses and large Xenos were such a strange step for Yamaha. They had really good, lightweight designs, built well, and they moved to really heavy overbuilt designs, still built well.

I bet you could trade in or sell that Yammy for enough to offset the cost of a used Edwards bass.