Since there are a few repair-type doodz (also doodettes?) as well as
generally-knowledgeable players on this list, I'd like to ask a question:
Q: On a moving rotary valve, do the sides of the "barrel" touch the casings
as they spin? ...or do ONLY THE BEARINGS (top-and-bottom "axles") touch?
This is a semi-trick question because, if properly fitted and oiled, I'd
think that the metal never touches as the bearings are riding on a cushion
of oil. However, this ain't a perfect world, and for proof, one need only
listen to an entrance I recently made while playing in an orchestra.
I reckon the question I'm asking is; Does one need to oil the rotors, or
only the top and bottom bearings?
Don't get me wrong, I'm going continue to oil my valves ("heavy" on the
bearings, and "heavy" mixed with kerosene of trumpet valve oil on the rotors
themselves) and am NOT trying to get anyone to do differently. I'm just
wondering what NEEDS to be done.
I think I remember Prof. Pizka oils the bearings regularly, and the rotors
either occasionally or not-at-all. I will occasionally forgo oiling the
rotors each day, but I oil the bearings EVERY day... though this may be a
superstitious action on my part. His steady, long-term playing of the same
horn would make an excellent study for valve wear Vs. lubrication habits. If
Prof. Pizka told me he lubricated his valves with partially-hydrogenated
truffle oil, I think I'd AT LEAST look into doing the same!
What got me to thinking about all this was an automobile's valve-train. For
those of you who have some knowledge of how such things, the auto engine's
camshaft has a series of little oblong lobes (imagine a turning circular
part with a "lump" on the outside of the circle's surface) that turn as part
of a camshaft assembly. As this lobe spins around, it presses the valve open
in what APPEARS to be a metal-to-metal occurrence. However, it can't
possibly be so or else the valve gear would wear to a frazzle in a few
week's time. I'm sure there's a name for what's happening (and I'm equally
sure someone will soon post it!), but it's analogous to skipping a flat
stone across a pond. As long as the stone has pretty good speed, it will
skip across the water's surface, rather than sink. This hydroplaning action
has got to be why camshaft lobes don't wear to a frazzle in a short time.
Yes, the engine's camshaft lobes have a smooth and well-hardened surface
treatment, but that hardened surface alone wouldn't explain why my old Isuzu
Trooper can spin it's valve gear (and rods, and crankshaft, and...) for over
200,000 miles without a failure. I know the engine will eventually eat
itself, but for now it runs incredibly well for its age. Oh that I could do
the same!
So, I was wondering how much of this hydroplaning action goes on in a horn
valve, and what the timeline on valve wear would look like. I'm assuming
(danger! you know what it makes you when I assume?) that the lower bearing
sees the most stress (the valve's spinning action actually begins as a
wear-inducing "push-pull" event), and that, with time, the downward spiral
begins from there. But I don't KNOW this.
What say ye?
jrc
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