Gear Fix

Gear Fix for Athearn Axles

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Here's the reason your "Blue Box" Athearn engine clicks when running down the track. I've come up with two methods of fixing this problem.
It does not include buying a set of gears. This method may also be used to prevent this from happening. One method uses a lathe to make collars,
the other uses retainer clips. Both methods work, but the collar method is the better of the two.

February 19, 2013

Typical split gear on an
Athearn "Blue Box" SD40-2 engine.

The collar fix. The ID of each collar is different because the OD of the hub on either side
of the different diameters. I made these from aluminum. They can be made from brass.

Note the circled gear and the aluminum collars. They are very narrow to fit inside the plastic gear housing..

These are the retainer clips and the pliers used to spread
them so you can installed them. They were purchased
from McMaster-Carr. Part numbers for the purchased
parts are: 97633A120 - Black Finish Steel External Retainer Ring for 3/16" shaft diameter, gty. 100,
58225A42 Mini External Fixed Tip Retaining Ring Pliers
45 Deg. 3/16"-15/64" (5-6mm) Shaft Dia.,.023" Tip Dia.
I also bought two .092" Dia. 3/4" L Overall, 4 Flute
reamers to ream the bore through the gear when fitting
the collars. Delerin is quite pliable and it squeezes the
bore down. The reamer makes for a nice tight fit when
using the collars on the wheel axle half's. The reamers are
not necessary if you use the retainer rings. They do not apply a great force on the axle. Note how small the
retainer rings are on Lincoln's head.

Retainer ring mounted on ring pliers.

Placing a retainer ring on the hub of the gear. The open portion of the retainer ring goes 180° from the crack.

After I had assembled the truck for a test run I noticed
that every once in a while there was a clicking noise.
I deduced that it was the very tip on the retainer ring,
namely the ears used for the pliers to spread the ring,
so I clipped them off using a pair of side cutters. Do not
use a good pair of your cutters. The steel is hard and
can ruin the cutting edge of your side cutters.

Better view of the ear that needs to be removed.

Two retainer clips per side are installed. They don't apply
the same force as an interference fit collar and two wide is
all that will fit without running into interference. The
crack can hardly be seen. Unfortunately the high contrast
picture doesn't show this very well.

Here's a picture of a later model Athearn truck that has
the brass collars applied to fix the problem. The truck is
from a RS-3.

NOTE: I've done more testing of using the collars to fix the gear problem. Some trucks ran fine others still
have the clicking noise when they hit the tooth area with the split in it. I've also made washers to fit between
the bronze wheel bearing and the gear to keep the axle centered better on the Athearn truck shown in the last
picture above. So the conclusion is that it's not a 100% fix. I have another idea that I want to try out and will
post that here when testing is complete.

As of today (1-5-2024) more information has been gathered. Time for an update.
It will be posted as soon as I sift through all the inofrmation.

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