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Overhauling the Minitrix Nohab

Sometime things are left too long. The main errors in the Minitrix Nohab were taken out in 2001 when the loco got a DCC decoder and a new motor, but 20 years on technology is much more advanced. There exist much better decoders, now also with sound and there are the cheap chinese coreless motors that function much better than the Mashima from 2001.
The mean time saw the Kato version of the Danish Nohab in CFL disguise. This is a much better designed loco and runs excellent, but it has its own shortcomings with new and different errors. The main ventilator for the resistance brakes is missing there too. The announced NMBS version never made it to the shops.

Anno 2001: Producing a Nohab diesel from the Minitrix look-alike

Repairing the body

Photo 1 shows the raw product, only the most obvious of the many errors are highlighted. This is the old version from 40 years ago. The 'new' model of 20 years ago was virtually unchanged, making clear that they don't take the market serious.

main errors highlighted
Main errors highlighted

We can correct most of the errors with some work. First we can add all the missing ventilators and air-inlets. Thus start making a copy of the 2 original ventilators using 2 component silicon rubber. Then the square hood of the Norwegian version is cut out with a piercing saw. Using your mould add 2 new ventilators. I used 2 component UHU glue and casted the ventilators directly in place. Then cut out the space for the third ventilator for the air-cooled resistance brake and its 2 air inlets. You have to find a new ventilator from a different model. This one rather looks like a spoked wheel and is not entirely correct either. But read on for the second renovation. Note that this ventilator is missing on the 204/54 series of NMBS Nohabs, these didn't have a resistance brake.

rubber mould for roof
rubber mould from roof for extra ventilators

the old new roof
the repaired roof

The next photo gives the inside of the cab. You have to keep everything as thin as possible as there is only 1 mm space to spare.

inside of cab
inside showing the new castings

The next step was replacing the front skirts. First remove the N-coupling from the bogie. If you cut off the skirts then the bogie will fall apart, this because you have to shorten it as well to make it move inside the new skirts on the body.

bogie changes
The bogie with front skirt from below

Thus first drill a new hole in the bogie underside and thread for M1 and put in a fixing screw. Then cut off the skirt with a piercing saw. Fill up the front of the bogie part with Milliput to keep it together. Take care that it can rotate a little bit (depends on the track radius). The photo above shows the bogie. And yes the wheels are not very clean but do also show that only the flanges have been thinned on the inside to adapt to FS160 standards. The photo of the bogie frame shows the screw and the Milliput filling.

You can now fix the skirt to the body, using a thin backing of plastic and filling up with lots of Milliput. After the necessary sanding and use of car filler to smooth the front. Then cut off the buffer consoles and refix them in the right place about 1 mm lower. Turn a new set of buffers (3.3mm plate x 3.8 mm long and tapered shank 1.5 mm) on the lathe or minidrill and use a file to make them rectangular.

You then get something like this

the new skirt
The new front with skirt and removed third lamp with rectangular buffers.

You can see the modifications. This wasn't the best model I had available, but a try-out for more to follow. I made the error of first painting the green and then the yellow. Do it the other way round. First paint it completely yellow and then spray the green. Yellow is a difficult colour to get a good cover where as green covers very well. It needs a full repaint but the livery is pretty difficult to get right. When fixing the MFK coupling do use the hook only. The loop cannot go under the body here, making it more difficult to couple. When the loop is missing it is easier to add all the hoses for brake and steam pipes. They will follow in due time after restoring the livery. Adding a gloss coat to windows would help but the better option is to use clear plastic inserts. Missing are the steps below the body sideways from the bogie.

Decoder and Motor

the new motor
new Mashima 5 pole motor

This photo shows the inside with the Mashima motor and the Lenz 040 decoder. In 2001 this was a good combination but nowadays it is totally obsolete, newer decoders and motors have much better performance.


I would advise against putting in much time into making the wheels completely fiNe-scale. The original locos had spoke wheels with 12 spokes! Thus a black/brown treatment will help to camouflage this anomaly, introducing spoke wheels will be a step too far, hardly visible and too much effort to produce.

Anno 2022: upgrading decoder, motor and further refinements

The easiest part is putting in a chinese, 8 mm diameter with 2 axle ends. The new motor sits in a brass block of 10x10x17 mm with an opening of 8.1 mm. This part happened to sit on the desk for some different project, it can be a piece of plastic from the 3D printer just as well. The worm is mounted on a brass sleeve of 1.5mm od by 1.0mm id. The coupling on the left hand side was produced on the lathe from a piece of POM. The decoder here used for testing the running is a D&H SD18A. First attempts already show a good performance without any finetuning. It is certainly not equivalent to the Kato version but for a 40 year old loco it is pretty good. There is plenty of room for the final mounting of the decoder. The speaker can be put in the tank without milling etc as this part is 4mm high and hollow. There is a large gap on the left where decoder and stay alive can sit with plenty of room for extra capacitators in front of the motor, along the motor and the hole for the worm. The original print can be left off, the lamps replaced by leds.

A first impression of the running with a D&H SD18A sound decoder taped on top for testing. An update with final mounting will follow in due time.

loudspeaker in the tank
Loudspeaker in the tank

decoder + stay alive beside the motor
decoder + stay alive beside the motor

new developments

3D Print
trial print with a 3D printed head from the anycubic.

The 3D printer can be of use here too, either to make new parts or even to just make an entirely new cab. Pretty useful too for all variants that are never going to reach the market. Or just as pilot for other NMBS locos which use the same frame but have a totally different cab such as the 55 series Diesels.

3D View
design as state of the art 3D view .

test print
Close, printed as single item, but not good enough yet

test print fitted on MTX frame
Comparison against orignal MTX and Kato

The new cab fitted onto a MTX frame besides an original MTX and the Kato version. Obvious are the much too small front windows on the MTX version and the errors in the roof. To fit the new cab this MTX frame needs some modifications, this because the cab was developed for the Kato dimensions. Thus itfits the Kato Nohab frame without any modification, but lengthwise the MTX cab and frame are overscale. After a straightforward cut and shut the new cab will fit, basically this means shortening the frame by cutting off 2.75 mm from each front and rounding of the corners a bit further. The last step is making 0.5 mm deep slots for the cabin doors. There exists a huge space between frame and cab on top, thus fitting a sound decoder will not form a problem. There is enough space for representation of the inside of the cab with a bit of further cutting of the top front parts of the frame.

First attempt to get correct lining, not entirely to satisfaction, but it easy to print another one for further exercise.


It was a long route to a correct 52/53 performing on a fremo meeting, complete with glazing and cab and fitted with leds. To do are finishing the front skirts with all sorts of hoses etc. Also the cab should sit a bit lower, this involves cutting off the ladders from the frame and refit with better ones. This one doesn't have sound yet, but that is only a question of time.

However, the design desk already works on the next project:

class 55 design in genesis
Design of a class 55 in genesis.

Sound fitting the Kato Nohab

The Kato doesn't need a new motor it runs excellent, but sounddecoders are larger and you need to fit a loudspeaker. The loudspeaker is fitted in the tank, but you need to mill a pocket for it. Something of 11x8.5x4.5mm for the smallest of speakers.

milling the space for the speaker
Milling the space for the speaker.

The loco has a split frame, thus we need to separate the two pieces when we clamp it in the vise for milling. I put in a piece of 0.5mm plastic card and taped the rest of the loco to prevent any swarf entering the gears etc. Be sure to clad this new space with the thinnest of paper drained with superglue for electrical insulation!
Next step is finding place for the decoder on top. I put in a next18 decoder D&H SD18A (old model), the newer is a several mm shorter (and Zimo now has a much smaller decoder but is much more expensive of course). Because the decoder was quite thick I removed a piece from the double hood to get sufficient height. For mounting this decoder I replaced part of the print and had to connect up with wires to get the lamps working again. The print also carries 2x2 connections to both sides of the frame thus you have to inspect what to leave and what can be removed.

connecting the decoder with the print
connecting the decoder with the print using wire.

That is all there is, you fit the hood again and enjoy your sound loco. There was no stay-alive mounted, the thing already runs excellent without, thus why bother.

But of course the roof is not correct thus it can do with a new printed insert:

new roof
New roof insert for the Kato to produce a Belgian Nohab

copyright: Henk Oversloot
date: 21-october-2001
update: 9 June 2022