Complete remotoring of kleinbahn krokodil loco

I recently came across KleinBahn locomotives on Ebay. Never heard of them until then. Apparently they are a small local model train seller in Austria that makes Austrian/German? model trains. The general consensus was that the locos are good, but detailing is not like in Roco or Fleischmann.

So i grabbed some Kleinbahn locomotives from Ebay when i found a good deal. One of them was the famous “Krokodil” electric locomotive. The loco was in decent shape, but had trouble running when i powered it. As usual, my goal was to update it by adding LED lighting and a decoder.

Here’s what i found when i removed the loco shell.


I took this photo after some mods (like LED lighting) and milling out the middle area. But what immediately struck me were the 2 motors that independently drove the two trucks. The wheel arrangement was 0-6-0.

The drive mechanism was worm wheel, but with a twist !!. The worm was basically a spring mounted on the 3mm dia shaft of the motor(s).

LED lighting was going to be a breeze because the loco was big and secondly it used light pipes. So all i needed were 2 sets of RED and white LED diodes to do the job.

However the bigger problem was on the decoder side. There were 2 motors that needed to be driven. Each of these motors had a stall current of approx 1Amp. Higher than the rating of the ESU basic (700mA stall), my favorite decoder. So i would need 2 decoders, one for each motor. Then programming the decoders would become a slightly more complicated task of having to set them to behave as a consist. Also, this loco did not have a flywheel, something that i think gives good prototypical behavior in a model trains. And finally, the motors were 3 pole armatures. The newer 5pole armature motors are much more smoother.

So i made my decision. I would replace this 2 motor independent truck drive system with a single 5-pole skewed-armature can motor, using shafts to drive the truck assembly.

So i had solve some problems during this conversion.The big ones were.

1: I could not find any plastic worm gears to engage the spur gear on the truck. And i did not want to change the gearing on the truck. That meant i had to use the existing ‘spring’ based worm gear. So i had to make a bearing blocks to replace the existing motors.

2: The loco body shell secures to the chassis via a long screw that screws into a bolt hole on the chassis(next to the V in the above photo). My by new plan involves putting a motor in that area. So i had to figure out a new way to secure the body shell to the chassis.

So first i decided to make a bearing block that mimics the existing motor to mount the ‘spring’ worm. Here’s the existing motor with the spring worm removed. A good tug on the spring with a noseplier did the job. I was amazed at the quality of the motor. It was extremely well constructed. I hated replacing such a fine motor from the loco…


And here’s the bearing block i milled from some acrylic sheets i had. I wanted a 1/2″ thick sheet, but had only 1/4″ thick ones. So i superglued 2 sheets together. The result was quite good. A sharp HSS endmill cuts through the acrylic like butter. It was a dream to machine this plastic. Just make sure that the bits are sharp. Or else the plastic could melt.


I also installed a 3mm ID bearings that would support a 3mm shaft. The height of the shaft from the base matches the existing motor. The blue color you see is the marking dye. The screw hole at the bottom of the block secures the block to the truck, just like the motor. I made 2 such blocks, one for each truck.

Here you can see how the bearing block fits in place of the motor. I also milled about 0.1″ at the base area so that motor would not touch the roof of the loco shell.


A close up shot of the Truck/bearing block assembly. The bearing block also links the base of the loco to the truck.


Next step was to secure the motor to the base. So i made a motor mounting block from a 1/4″ scrap aluminum piece. I also had to turn down the heads of the M2 securing screws so that they would not contact the flywheel that would be fitted there. The motor was a great deal from Ebay. A 5 pole, skewed armature motor that draws about 500mA stall current. I was too lazy to clean up the blue marking dye.


So here’s the flywheel press fitted to the motor. I ended up making my own flywheel on my mini-lathe because i had some scrap brass rod pieces. Size is 17mmx11mm. The most frustrating part about making a flywheel with a Chinese lathe is to make sure it is concentric. Otherwise the whole loco is going to wobble like crazy @11000rpm of the motor!

Mine was good. Not as good as an NWSL flywheel, but definitely did not have vibrations at the full RPM rating. Thats a good sign.


Next, the ‘spring’ worms were fitted on 3mm shafts (from McMaster). I used nylon washers on either ends of the bearing blocks and finally the assembly was secured along the shaft axis by using E-clips. At the opposite end of the worm was an NWSL 2.0 universal joint assembly. This was a great U-joint coupler system. Affordable, strong and small for a HO scale. The motor was secured to the base of the loco with 2 screws mounting from under the base, securing to the motor mount block.

The little assembly on top the motor  addressess one of my original issues on how to secure the shell to the chassis. The cylinder at the top is a spacer nut tapped with #2-56 threads. This nut connects to the motor block. The shell has a securing screw hole on the roof that allows the shell to be secured to the chassis.


Closeup the of the motor block, the bearing block and the couplers.


Skipping some steps, here’s a photo with the DCC decoder and lighting block. The decoder is an ESU basic decoder. I never connect the decoder wires directly to the motor, tracks or lights. Instead i make a connection PCB which in turn connects to the tracks, motors and the LED’s. The LED’s used were 0603.


A closeup shot of the LED’s. The resistor is a 0805 1K.


Closeup of the decoder wiring. I used the thin 0.5mm ESU wires for wiring. They are amazing!!

Again, the black stuff you see is the liquid-tape from home-depot. Used as a glue to secure wires to the frame. The best part is that bond is not very strong. So if rework is needed, take a toothpick to peel the layer off.


Another shot of the assembled loco. This then got tested on the track. It runs good, albeit with some higher noise. I guess it is the extra rotary contacts like the bearing blocks. Next time i think i’ll use Acetal bushings instead of metal bearings. Less noise.


Another shot. I left the marking dye as a reminder to myself on the work it took to remotor this loco.


The final assembled loco. It looks great !!


Running test while pulling a lighted passenger car….



I am a computer engineer living in the beautiful city of Austin,TX. While my day job is designing computer chips, I love to dabble in woodworking, metalworking, r/c and electronics.

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Posted in Metalworking, Model trains

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