Rebuilding the drive train

In their original condition both models were equipped with an open gearbox driveline that was coupled to an old open frame motor. Plastic tubing was used to couple the drive line across the articulating joint in the locomotive. Noisy metal universals coupled the motor to the driveline. The photo below shows the original drive train in the locomotive:

In the original condition the locomotive was quite noisy due the metal universals and the open gearboxes. The entire driveline needed to be replaced to improve the performance of the locomotive.

These locomotives turned out to be one of the most challenging re-gearing projects that I have encountered. Unlike most model locomotive frames the Akane’s were built from a simple brass U channel. Only a narrow slot was cut in the frame to allow the axle gear to protrude through. Fixed brass bearings on both ends of the worm held both the worm and the driveline in position. The original axle gear was a 37 tooth 0.4 mod gear.

The new replacement gearboxes from NWSL are 0.4 mod with a gear reduction ratio of 28 to 1. The lower gearbox ratio matches up well with the slower replacement 20mm can motor. Since the 28 tooth gear is smaller than the original 37 tooth gear the new position of the driveline is closer to the frame. In the new position there is only 25 mils clearance between the frame and the bottom of the driveline. Due to this low position the frame had to be milled out to clear the new universal joints. In addition the new gearboxes are much larger that the original holes in the frame. The frame and bottom plate both had to be milled out to provide clearance for the gearbox.

The following photos show the modifications needed for the new driveline components:

The blue arrows in the photos above show where the frame modifications were made. Notice that one of the gearboxes had to be notched to clear the valve gear hanger that sits flush with the top of the frame. The frame cutout for this gearbox also had to be enlarged to allow the gearbox to drop in behind and then slide forward under the valve gear hanger.

Instead of the fixed rigid bearings used in the old design I made one floating bearing for each gearbox. The bearings act as a torque arm to keep the driveline in its proper position. A small washer and a 1.4 mm screw secured the bearing to the frame, but the clearances were designed so the bearing could freely rotate in its mounting hole. As a locomotive goes around curves the wheelsets tend to shift from side to side in the frame. The bearings were made to rotate so that gearboxes could freely shift back and forth with the wheelset movement. The universals easily compensate for the slight longitudinal rotation of the driveline as the wheelset shifts position from side to side.

Here’s a close-up photo showing one of the bearings with its mounting washer installed:

The photo above is also a good illustration of just how close the driveline sits to the top of the frame. The shaft material is 2.4 mm, or 94.5 mils in diameter. From the photo you can see that there’s only about a quarter of the shafts worth of clearance to the point where the frame sits. Also note that the universal on the left extends below where the top of the frame would be. From this photo its clear why the frame has to be milled out to clear the universals.

Here’s another photo that shows some more modifications needed because of the low driveline:

The red arrow on the left shows the area on the valve gear hanger that required milling (.010”) to provide clearance for the drive shaft. Also note how the notched gearbox just fits behind the hanger. The back edge of the cylinder block also had to be cleared in the area of the arrow on the right.

This photo illustrates the mounting of the new motor and flywheel:

I fabricated the motor mount from a piece of 1/2” x 3/8” brass bar stock. On the top of the mount I milled out a motor cradle with a ¾” (19mm) ball end mill. The base was fly cut at an angle to position the motor on the correct mounting angle. The base of the mount is also tapped for a pair of 2mm x 0.4 screws. These screws secure the mount to frame, and allow for easy removal of the motor assembly. The motor is secured to the mount using silicon rubber adhesive. I also made a custom tapered flywheel to fit in the space that was available.

This photo provides a good comparison of the old and new drive lines: