K-Series Rebuild

Getting Started

Whether you're experienced with Nathan Airchime horns or not, rebuilding your horns can be challenging due to the lack of resources available online. Whether you're a seasoned train horn vet or not, this guide is sure to help you do a complete rebuild of your K-series train horns.

Nathan Airchime K5LA Train Horn
Nathan Airchime K5HA Train Horn

Nearly all Nathan Airchime K-series horns are setup with either 3 or 5-bells, all mounted together on a base known as a manifold. This manifold routes air from your air supply into each horn. Below is a picture of a high mount manifold without the bells installed.

Nathan Airchime K5HA High-Mount

The LA in K5LA signifies that the horn is a low-mount style, where each bell is mounted side-by-side, on a flat base.

Nathan Airchime K5LA Low-Mount Train Horn

Example of a K5 "Low Mount"

The HA in K5HA signifies that the horn is a high-mount mounting style, where the bells are stacked similar to a Christmas tree.

Nathan Airchime K5HA Hight-Mount Train Horn

Example of a K5 "High Mount"


Each horn bell contains one diffuser ring, two stainless steel diaphragm discs, and one diaphragm cushion. The order in which these components are re-installed is important.

Nathan Airchime K-Series Diaphragm Kit

Each bell has a cap on the back side that can be removed. Using a wrench, remove all six bolts from the back-cap. Be sure to hold onto the back-cap after removing the last screw so that it doesn't fall.

Nathan K-Series Train Horn Back Cap

Once the back-cap is removed, we can start digging into the internals of the bell.

Your bell should look similar to the one pictured below once the back-cap has been removed.

Nathan Airchime K-Series Sound Chamber and Diffuser Ring

Top-down view into the bell

When the back-cap is removed you will gain access to the diaphragms, cushion, and diffuser ring. The diffuser ring is the ring in the center held in with three Allen-head bolts. This piece can be replaced if needed, but is usually okay unless bent/damaged/corroded. If you don't immediately see the diaphragm and cushion after removing the back-cap, check inside the back-cap. In most cases, the diaphragms and cushion will get stuck inside the cap and will remain attached after removing the cap. You can give the cap a light tap on a hard surface to break the diaphragms free, or use a small toothpick to pry it out.

Now that your bell has been disassembled, we can now put it back together with new diaphragms and cushion. The diaphragm cushion will be sandwiched in between the diaphragms upon re-assembly. Line up one diaphragm over the center of the bell. Place the diaphragm cushion on top of the disc, and place the last diaphragm over the cushion. The image below shows a blown up view if the assembly order.

We find that putting this together is much easier if you put the diaphragms/cushion into the back-cap first, and then re-install the back-cap to the bell.

Nathan Airchime K5-Series Train Horn Diaphragm Assembly

Once the internals have been lined up, carefully press the back-cap over the bell and rotate it so that the mounting holes line up. Re-insert each bolt and tighten each down finger tight. Use a wrench to carefully torque each bolt down and alternate each corner as you go to ensure each is tightened equally. Do not over-tighten these as you can possibly warp the aluminum.

Testing The Bell

Each bell can be tested individually with a rubber-tipped blowgun. Line up the nozzle on the blowgun with the small inlet hole on the bottom of the bell. This hole is located in-between the two ears that are used to secure the bell to the manifold. The inlet of each bell is approx. 3-4 mm across. Each bell should sound off extremely loud, even with a blowgun. If your bells do not sound off at all, your internals are likely stuck in the back-cap. This occurs if there is some dirt/build-up on the inside rim of the cap. A sanding pad can be used or scotch-brite pads can be used to remove dirt/grime build-up on the inside of the back-cap. 3M makes a personal use sanding sponge that works well for this application here.