Class 37

5″ Gauge Class 37 diesel locomotive – ex Works in 2003

This new loco was started in February 2003 as an improvement project to my old over-scale, Maroon, diesel outline loco. The first job was to replace the heavy metal body with a near to scale GRP one, which would be much lighter and easier to handle. The chassis would need reducing in length by about eight inches and the two C5 motors lowered into the bogies as they were too tall. It was also intended to modify the existing bogies with ones, near to scale so a manufacturers drawing was obtained for this purpose. The main aim was to reduce the overall weight from about 240lbs down to about 170lbs making it easier to handle and less difficult to load and prepare for duty.

The old steel bodied loco

Once started, it soon became apparent that a new chassis would have to be made, this was because the (old) batteries fouled the new body roof line by about 15mm! A new battery sub frame was in-built to accommodate this requirement. But this also showed up another problem in that the frame clearance and bogies were going to clash so clearances needed to be detailed and designed fit for the purpose. So, we now had a new body, a new chassis and new scale like bogies. Efforts to obtain a fourth C5 motor did not bear fruit so we now had to go for replacement traction motors. What had now developed into, by stealth, was a complete new engine that would incorporate the existing 4QD controller and two (new) 85 amp batteries. two new 250 watt Fasco 12 volt motors were obtained for this loco, these would be mounted horizontally in this loco. A 3 to 4 week upgrade had turned into a 6 – month project.


In its first guise

This class 37 loco would be very near to scale and have features not dissimilar to the refurbished DRS class 37 locomotives that were appearing on the main line. Direct Rail Services used a colour that best matches Oxford Blue, a Black roof, Yellow nose ends and Red buffer beams. The under-slung fuel and water tanks are Black.

It was decided to use car body spray paints “Hycote Cellulose” to finish the bodywork. Not only would it result in a good finish but should also be a cheaper option.

undergoing a repaint to DRS colours

The traction system would use my 4QD 120 professional controller and existing 75 amp traction deep-cycle 12 volt batteries, at least whilst under testing.

From information obtained it was decided to buy two 250 watt (Fasco) high torque starting, traction motors from Parkside. I would first try two, to check 500 watts performance and if these were under-powered a third 12 volt motor would be added latter.

This engine now has 3 motors fitted, giving a total of 750 watts output, ironically, I did look at using the Bosch 750 (24v) but at £152 it seemed expensive against £37 each for the 250’s. Two of the motors have been fitted with 42 amp cables. (The Bosch 24v motor will deliver 1hp and does it well, if you have the space to fit one of these, do it!) I was looking at obtaining 8mph (9mph as max) performance using the Fasco motors that should be powerful enough for requirements and safe public running.


New light clusters in the WIPAC style, suitable for the DRS Class 37s that the locomotive was modelled as.

I used several scale looking plans to “size the engine details” laid out to 5” size, I then enlarged to 5” scale, some of the detail photo’s I had taken of this marque of engine and pasted them on top. I took many measurements off the full size loco and checked these against the plan. Some adjustments of size then gave me the working details to make the scale like parts for 37EE3. A few compromises were necessary but overall you can arrive at a good likeness of this loco. The GRP body does not precisely match scale in several areas but it is as good as I need and when finished certainly looks the part. It will give many people lots of pleasure both to drive and to ride behind. In any event, minor alterations were to be expected in design and build project such as this, I drew lots of detail sketches before adding the dimensions and trial parts were sometimes made in non-metal materials before manufacturing the real items. The big problem with this one was that you needed multiple parts made and the swarf tub soon fills up. It also became essential that jigs/tools and fixtures were made to advance production and maintain standards of parts in a series of set-ups.

The new drive system, as described

The new drive system, as described

An interesting point, 4’ 8½ inches is 4.71 feet, multiply this by 1.062 and you come up with Five inches. OK.

I used several sources for obtaining materials, these can be expensive, if you did get an extra bit or two, to allow for mistakes! Mistakes can be costly!


Finished locomotive out for photos in the sunshine

One thing that needs very careful thought is the electrics, some might think that “its only a car battery” not in this case! We are now using 12 volt, 85amp, Semi traction, deep cycle batteries. Short these out, and you could have 300 amps giving you some nasty burns or worse! I always ensure that I have protected terminals to my batteries, if they have exposed post or lugs then make some form of protective barrier, and FIT IT.

Mistakes are easily made, you might be distracted at a crucial moment, don’t let it happen. Also make up your cables and connections so that they can only be connected, one way. If it’s not long enough, it won’t reach (a wrong terminal), colour code them as well. Make sure that your cables are heavy enough to carry the load without heating up. If you follow these simple rules you should avoid disaster! Not all control systems have polarity protection, are fused, or even have an isolator. Remember, if you can disconnect it quickly it might save you from an unwelcome visit to the surgery or hospital! These replacement batteries fitted but the protective handles once again fowled on the inner roof curvature!

You could decide to buy in the bits and make up your own loco from these, instead of spending many hours making them individually. Several suppliers can help you with all sorts of component parts. To buy a ready to run one like mine works out about £3,750. To make it yourself from scratch, knock £2,750 off the price! I all ready had certain items that could be co-opted to get it working and then considering options after trials were completed.

One very important fact to remember, us oldies can’t do what we used to take for granted, it either takes twice as long or its too damned heavy! Also bear in mind that it won’t fit into your car boot! It’s too long to go in the estate car or van and how many navvies will it need to load and un-load the thing!


Will this one go in the back of the car? Can I take it home?