This week I decided it was time to change the rotor stops (bumpers) on my horn. When I bought the instrument back in February of 2011, it came with silicone rotor stops. These worked really well, but over time they have swollen – a reaction to my valve oil, I assume – and even started to tear apart in a few places.

Changing rotor stops is not difficult, and requires about the same number of tools as restringing valves. Here’s what you need.

1. Small screwdriver
2. Exacto-knife or razor blade (use caution)
3. Needle-nose pliers
4. Cutting surface
5. Rotor stop material

The screwdriver is used to remove the old stops, and to install the new ones (more on this later). The knife is used to cut and trim the rotor stop material, and I highly recommend using a pair of needle-nose pliers to hold the material while doing so – it’s much safer this way!

Materials used for rotor stops have changed over the years, from cork to various kinds of rubber and silicone.  I ordered mine from Osmun Music, who sells lengths of  Buna-N synthetic rubber in varying diameters and consistencies (duro).  Here’s what it looks like.

Once you find and order the correct size, you’re ready to change the stops. First, remove the old stops using the small screwdriver. I prefer to change the stops one at a time rather than removing them all at once. I use the same procedure for restringing because it makes it easier to keep track of all the parts. I used my old stops as a rough guide for trimming the new stops. Use the pliers to hold the material on a durable cutting surface – a block of wood works well- and cut carefully. Cut less rather than more, as you can always trim away more material if necessary. Install the new stops using the screwdriver to push the material into place. You may have to do this a few times to get the material  situated. Once you’ve done this you need to check the alignment by removing the valve caps. If the stops are cut to the proper size and adjusted correctly, the notches on the top of the bearing should line up with the notches on the bearing plate, as shown in the video below.

If they don’t line up you’ll need to trim away some material until they do. Here’s a picture of the newly installed rotor stops.

One thing I’ve noticed since changing the bumpers is a distinctively different feel to the valve action. The Buna-N material is less spongy than the silicone, and therefore gives less when the valves are moving back and forth. I prefer this more solid contact, and to me it actually seems like the valves are moving faster and more precisely. As with rotor string, it may be worth trying some different materials on your horn just to see if there is any improvement.  One other reason to know how to do this simple procedure is because there are lots of school-owned horns out there in various stages of disrepair. I’ve seen numerous students with horns whose rotor stops are worn, misshapen, or just plain missing, with any number of stand-in materials used: pencil erasers, bits of rolled up paper, etc. Needless to say, this probably had an adverse affect on their playing.