How NOT to build a kit - Part 1

A Class 31 Diesel Locomotive - Rescue

Modern Motive Power state very clearly that none of their kits are suitable for beginners or those with no kit building experience. This article should not reflect badly on Modern Motive Power or any of their kits.

My own view is that if you are going to build something of the complexity of the Class 31 locomotive that I am going to show here then it would be better to start with a brand new kit. Those of you buying kits from e-Bay are risking wasting your money, there could be parts missing, you have no idea how well any construction that has already been done has been implemented. So my advice is, unless you are getting the kit for some ridiculously low cost that will not hurt your pocket if it turns out to be a pile of scrap, stay well clear.

If this locomotive did not belong to a very good friend I would not have gone anywhere near it. The owner did tell me to look in the box and make a decision and if that decision was “its scrap” to put it in the nearest bin. Having evaluated the contents I decided it wasn’t quite that bad but it was a close run thing. So the locomotive will serve a dual purpose. I will get a Class 31 on the website and on the way I can show you some construction techniques and how to rescue the seemingly impossible when things go wrong. We all started somewhere and we have all melted or destroyed something along the way although doing it with an MMP Class 31 seems like a very expensive way of doing it to me. I have no idea who started building this kit and to be perfectly honest I don’t want to know, if you recognise this as your “handy work” you should have started with something a little simpler.

 So lets see what we are faced with.

Class31_1 Class31_2 

This group of four pictures is of the inner bogie chassis.

Picture 1 – Top Left 

It’s not an optical illusion, yes the right hand chassis is banana shaped – I checked it on a piece of glass.

Picture 2 – Top Right 

The top chassis has not had the section removed where the motor sits, this would be a pig to remove without distorting the chassis, as it is the chassis is already distorted so it doesn’t matter at this stage.

Picture 3 – Bottom Left

This picture is a blow up of picture 1 and shows more clearly the seriousness of the situation. All of the brass bushes for the axels have been passed through from the wrong side, non of the lamination is correct and the most serious error is the floating frame for the centre and front axels which should be supported by a piece of 2mm rod passed through the outer frame with the arms free to swing about their centres. Here they are supported by a copper nail which is substantially less than 2mm diameter and is soldered off centre, the brass bush is also not soldered in square. Bottom line, there is no way this bogie would have ever run correctly.

Picture 4 – Bottom Right 

Apart from the fact that the plate where the motor sits has not been removed, basically nothing is square, almost non of the folds are 90 degree, this is very important where the two plates slide in that support the motor, the degree of error here needs to be under 0.5mm. I don’t know what all this was soldered together with but flux does not appear to have played a part in the proceedings, this is actually an advantage to me because it means none of the solder has penetrated very deep into the laminated parts which are going to have to be completely stripped down, cleaned and reassembled. The whole thing is also coated in something greasy that resisted standard cleaning.


While it would be nice to strip it all down and flatten everything out this is not practical. The half etch lines that form the edges will probably not withstand being folded back and then folded again to the correct angle, we would then be in a worse situation because the basic geometry  of the chassis would be lost.

So, 2 hours work with a 75 watt soldering iron, a small gas torch and several meters of desoldering tape brings us to the picture below


Some extreme heat was applied and as much solder removed as possible using desoldering tape, this was sufficient with some parts and they just fell apart. Some parts  required direct heating from the gas torch and gentle prizing apart using a sharp knife blade. As you can see I have splayed the chassis sides slightly in order to do the final clean up before reassembly. The next step is to remove all the remaining solder using a glass fibre brush and fine wet & dry paper, then a final clean up in hot soapy water. The final picture in this section shows the end result.



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