French Horn Rotors

How to Service
French Horn Rotors
by Jeff Smith
With a few simple, affordable supplies and this
step-by-step guidance, musicians and music directors
can easily learn to service rotor valves. This can be of
great benefit in both emergency situations and as a matter
of regular maintenance. While there are many points of
service that can be attended to without great investment
or advanced skill, there are still many areas of repair
(beyond the scope of this article) that must be referred to
professional technicians.
Cleaning
and Lubrication
As a musical and mechanical necessity, rotor valves have
a very tight clearance between the rotor and valve casing
and at the bearings. Because of this, any deposits on any
part may cause the valve to lock in place or freeze up. This is
most likely to be experienced after the instrument has been
unused for some time.
Playing the instrument daily tends to keep minerals and
lubricants from hardening into deposits. This is particularly
true if the musician lubricates the rotors frequently. The
lubrication helps the valve shed any contaminants, and fills
the space that would otherwise attract water-born minerals,
which create deposits.
Often you can free a stuck or sticking valve without
disassembly by lubricating the rotor through the slide tubes,
and working the rotor stop arm back and forth by hand.
Pulling the valve slides, put two drops of valve oil into each
tube on the horn. Don’t turn the valve using the levers, but
rather by directly turning the stop arm (fig. 1). Also put a drop
on the back bearing (after removing the cap), and the top
bearing (beneath the stop arm).
To clean a valve requires disassembly. First unscrew and
remove the valve caps. If these are frozen, tap lightly on the
knurled (grip) area of the cap in a glancing counter-clockwise
manner (as if trying to unscrew the cap). If the cap is still
stuck, apply a drop of penetrating oil to the joint of the cap
and casing, and try again after the oil has been allowed
to penetrate.
Loosen the main screw (fig. 1) a turn or two, and tap on this screw to release the rotor from the bearing.
Completely unscrew the main screw allowing the rotor to be pulled from the casing. If you are removing
more than one valve at a time, keep them in order so that you can get the rotor in the correct casing when
reassembling.
Protect the rotor by working over a table covered with a soft towel to receive the rotor if it falls. Also protect the
bell stem of the instrument so that if a lever arm releases, the spring tension won’t slam the lever into the bell
causing a dent. Control the levers while tapping the rotor loose.
Stops (2)
Main Screw
Rotor Stop Arm
The rotor is now available for cleaning. While a scrubbing in soap and water may bring results, more often
you will need to soak the rotor in a chemical to remove deposits. White vinegar is a good solution for the
nonprofessional. You may wish to pull all the slides and rotors and give the instrument a brush-through in a bath
of lukewarm water and mild dishwashing detergent. Rinse thoroughly, and allow to dry before assembling with
fresh slide grease and valve oil.
1
“Cork” Plate
Cleaning the valve casing of deposits is problematic because it requires a larger tank of solution. I would refer
this to a technician. Many professional shops use ultrasonic cleaners and more aggressive chemicals for
this task.
Wiping both the casing and the rotor with a lint free cloth, dry test the fit of the rotor. If you are satisfied that
the valve rotates freely, reassemble the valve with fresh oil, adding a drop of rotor oil on the bearings and the
threads of the valve cap. Place the stop arm back onto the rotor and set the main screw. Be careful not to over
tighten this screw. This task can be clumsy if the string is still attached. You may wish to detach the string and
restring it after assembly (see next page).
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How to Service
French Horn Rotors
by Jeff Smith
Continued
Adjusting Rotor
Port Alignment
In order for the instrument to play its best,
it is necessary that the rotor valve ports
align correctly with the tubing to which they
direct the airflow to (fig. 7). Taking the valve
cap off the rotor, you will see corresponding
marks in both the rotor shaft and in the back
bearing. You will also notice a small notch on
the outer edge of the back bearing (fig. 9).
1. Align the notch in the back bearing with
the corresponding notch in the valve casing.
This bearing is gently pressed into place. If
it is not located correctly, loosen the stop
arm main screw (fig. 1) a couple turns. Tap
on this screw to release the back bearing,
rotate the bearing to its home position, and
tap it back into place. Reset the
main screw.
Note: when securing the bearing, it is best
to use a plastic tube (or a dowel with a
center hole), which fits over the center
of the bearing. Tap on this tube to equally
distribute the pressure applied by the
hammer.
2. Moving the rotor stop arm all the way
in each direction, observe the position of
the mark in the rotor in relation to the mark
in the bearing. These must align perfectly
when at each stop
(fig. 10 & 11).
3. This alignment is adjusted by changing
the size of the rotor stops. The rotor stops
are often neoprene, sometimes cork. The
JLS kit includes neoprene. Use this to
replace stops that are missing or too small
to be adjusted. If the stop is too large, it can
be cut back with a razor blade.
4. While it may be possible to insert
new stops while all parts are assembled,
it sometimes is necessary to remove the
cork plate from the casing (making a bigger
job). The stop material often needs to be
squeezed with pliers or stretched to fit into
the plate. The material will then expand to
fit securely in the cork plate. If you remove
the cork plate, you can hold one end of the
neoprene in a vice, which easily allows
you to stretch the material and insert it into
place. Trim the excess on each side of the
plate with a razor blade.
7
8
9
10
11
Notch
Rotor Valve
Schematic
Back Bearing
Rotor
Shaft
Adjusted
Misadjusted
Restringing Guide
These instructions include the use of the
JLS #206058 Valve Restringing Kit.
1. Set the Stringing Jig in place over the
lever touch pieces as shown. This will keep
all levers on plane with each other. (Note:
if all valves are being restrung, you will
determine the touch piece height when you
secure the first screw in step 6).
2. Loosen the rotor stop and the lever string
screws and remove the old string. Don’t
loosen the screws more than enough to
remove the old string (we don’t want to
lose them).
3. Cut a new piece of string about
8 inches long.
4. Tie a knot in one end. This will act as
a stopper to keep the string from pulling
through, so make the knot larger than the
hole in the lever arm.
5. Thread the string through the hole as
shown in fig. 1. Tip: if you cut the string at
an angle, you can pass it through the hole
easier. Use a sharp razor blade to make
this cut.
6. Holding the rotor arm in the position
shown, wrap the string as in fig.2, making
sure that the string goes under the screw.
Continue wrapping as shown in fig. 3.
Secure the screw (don’t over tighten).
7. Continue with the string as in fig. 4, then
take it through the hole (fig. 5), and wrap it
under the screw. Secure this screw.
8. When at rest, the arm of the lever will
usually be set at an elevated angle to the
rotor so that when the lever is pressed
the arm won’t be too low (which can
cause binding and noise) (fig. 6). It may be
necessary to re-align the lever arm to the
touch piece. The alignment is performed
by holding the touch piece and bending the
end of the lever either up or down. The lever
ends should all be on plane with each other
just as the touch pieces were.
9. To add a professional touch, clip the ends
of the strings so that they are the same
length. To allow for possible adjustment
later, leave the unknotted end at least
3/4" long.
1
2
3
4
5
6
Stops (2)
Main Screw
Rotor Stop Arm
“Cork”
Plate
Hold
Over
Lever Slightly
Higher Than
Stop Arm
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