Welcome Guest ( Log In | Register )

Bachmann Class 20

BR Class 20 Bo-Bo diesel electric

Review & DCC Decoder installation - by Doug Teggin


right: BR Class 20 D8000 that can now be seen
at the National Railway Museum in York.

Prototype Info

The British Railways Board's 1955 modernisation plan called for a change to alternative forms of traction and manufacturers were asked to produce trial or small initial builds for evaluation. English Electric submitted an existing design based on an export model for a 1000 BHP diesel and 20 were built as a pilot scheme for assessment. The first batch was built in 1957 and the diesels were assigned to work from Devon's Road depot, East London.

The design was a success from the start and by 1962 a total of 127 had been built. Following assessment of all the Type I diesels, BR placed a further order increasing the total to 228 by 1968 and the design became the BR standard for 1000 BHP diesel locomotives.

With the introduction of the TOPS code system in 1968 the diesels were designated Class 20 and renumbered 20 001 to 20 228. The diesels were principally designed for freight work but also saw service on summer passenger trains (no train heating for winter). The Class 20's worked over the Eastern, London, Midland and Scottish regions. The only drawback the diesel has is one cab, unlike modern designs that have a cab at each end. BR resolved this problem by operating the diesels as pairs, nose to nose, and with the combined power of 2000 BHP they were able to haul the heavier block freight trains. BR's decision to switch to Type 5 and in particular Class 60 diesels in the late 1980's started a gradual withdrawal of the fleet with just 28 left by 1994.

The last 100 locomotives to be constructed were fitted with head code boxes (D8128-D8327), the rest used the disc system.



A tribute to the design is that after 45 years the Class is still in service with DRS on mainline duties and at least 28 of the class are now preserved.

Several of the existing locos, which are operating singly, have been fitted with nose-mounted video cameras in order to solve the visibility problems.

DRS' fleet of class 20/3s see frequent work across the country in pairs, or with class 37s on nuclear flask trains, which the company specialises in.


Other Industrial use

Several have been sold to industrial users such as Lafarge Cement. Some were used on the construction of the Channel Tunnel and Channel Tunnel Rail Link and some even made their way to France to work in industry there, although some of these were recently repatriated. Currently some class 20s owned by HNRC are working some trains within the Corus steel works at Scunthorpe. Some were also converted by Hunslet-Barclays to weed-killer units. These units would spray a weed-killer onto the track bed.


Class series Nos: 20001-20199, 20200-20228 Traction motors: four EE526/5D or EE526/8D
Original series Nos: D8000-D8199, D8300-D8327 Maximum tractive effort: 42,000lb/f
Builders: English Electric Co Ltd and Robert Stephenson & Hawthorne, Darlington Continuous tractive effort: 25,000lb/f @ 11mph
Introduced: 1957-1968 Maximum speed: 75mph
Engine: English Electric Co 8SVT, Mk2 8-cyl, pressure charged Weight: 73-74ton
Engine BHP: 1000 @ 850rpm: Brake force: 35ton, Vacuum/Air
Power at Rail: 770hp Length: 46ft 9in
Transmission: Electric Fuel capacity: 400gal
Main generator: EE8 19/8C Route availability: 5
Auxiliary generator: EE99 1/28 Driving wheel diameter: 3ft 7in

Unusual class 20 facts

In the 1995 Bond film, Goldeneye, a British Rail class 20 No. D8188 was used as an escape train, with the addition of armour plating, to give the impression of a Russian Armoured Locomotive. The locomotive was disguised to look like a Soviet locomotive for one of the film’s major stunt sequences where it collides with a tank; the dramatic scene was filmed on the Nene Valley Railway.


Bachmann Class 20 - Model Info

D8134: Bachmann Railways Model No 32-028
"Class 20 Diesel - D8134 BR Green with indicator boxes" - Released 2003

D8046: Bachmann Railways Model No 32-027A
"Class 20 Diesel - D8046 BR Green with indicator discs" - Released 2004

This is a sort of 2-in-1 review as there are actually 2 locos here on the bench. D8134 has indicator boxes and D8046 has indicator discs. As these two models are very similar I thought that they would make a fantastic pair running around as a multiple Unit on the layout. Individually, they are excellent models: strong, compact, simple and efficient. Together they are very strong and work together in an elegant configuration.
D8134 (indicator boxes). Released in 2003. Very good motor with twin brass flywheel. Pickups on all wheels and all-wheel driven. Sturdy construction and heavy ballast built into chassis.
D8046 (indicator discs). Released in 2004. Same as D8134 in virtually all respects. Slightly more detail: Ladder (front right), 4 sets of sanding pipes as opposed to 2 on D8134.
I have added the detail pack to the loco and find that the pipes gets in the way of everything. They are not really designed to be added to a working loco as they even hinder the bogie movement. I'll add the details to the second loco when I know that I'm done working on it.

The locos both have reasonable detail. A fan on the roof actually turns if you blow on it. The cabs are not as detailed as some others that we have seen recently. There are sliding cab windows in D8134, but one has already come out. It was loose in the cab on arrival and there is no obvious way to get in there and fix it - I eventually managed to extract it with long nosed pliers. The cab is attached to the body with melted plastic tabs. You will notice a largish gap between the yellow of the cab and the red of the buffer beam - a symptom of the building method. The D8046 loco cab is much better fitting.


So we need to get these guys hooked up and working together. The best way is by using a multiple unit (MU) configuration in DCC. It could be done as a double header (DH), but as the prototype worked nose-to-nose so that there would be a cab at either end to improve visibility, the default direction of the leading loco would have to be reversed using CV29. Double heading assumes both locos are running in the same direction. A MU is very similar, but can be composed of more than two locos and each one when added to the MU, can be configured to run forwards or backwards. So when the MU is disassembled, the locos can operate normally as single units right away.


DCC Decoder Installation

The choice of decoder is the Lenz Gold-JST Silent-Back EMF DCC Decoder (Article Nr. 10433).

The decoder can handle a continuous current draw of 1.0 Amp with a peak current for short periods of 1,8 A. Some of the main features are:

  • Super smooth and silent high frequency back-EMF motor control.
  • Supports the industry proposed enhancements to the NMRA DCC
  • Bidirectional data communication RPs
  • USP with optional power module for operation on dirty track
  • Asymmetrical DCC support including directional stopping
  • Adjustable precision stopping control
  • Low speed gear for switching operations
  • Motor and function outputs protected
  • Four function outputs rated at 200mA each with advanced function mapping
  • Directional or independent lighting with dimming and special effects.
  • Support for Advanced Consist Control and Extended Addressing
  • Support for programming on the mainline (operations mode programming)


Above are a pair of the Lenz Gold-JST decoders with their harness and NMRA Medium Plug. They are double sided. Not too small, but fine for most HO/OO installations.


Remove loco bodies. Above left loco has NEM socket protection plug removed, loco on right has plug still fitted.
I remove all capacitors in parallel with the motor circuit. We have discussed this on the forums and the general consensus is to remove them. Capacitor on the left gone, the one on the right about to get the snip. Both capacitors now removed and the decoder attached to the front of the chassis with double sided sticky sponge. Make sure it can't get loose and make sure there is no possibility of any electrical contact between decoder and chassis. NEM plug fitted with orange wire in socket hole 1.


Secure the wires and make sure the flywheels are not obstructed in any way. Even though there is plenty of space in the body, the fan structure is situated just where the decoder wires are folded. Keep them as flat as possible. Replace the bodies.


The locos are now ready to be programmed and coupled together. Program the 4-digit long loco address on the programming track then you can do the rest on the main line if your system supports programming on the main (PoM).
I set up a multiple unit at address 20 as the front loco has that on it's indicator box. Makes it easier to remember. You can also call up the MU from either loco long address when set up though.

Follow your DCC system's instructions for setting up a MU. On my Lenz system it is typically long-winded. Function F3 and then a whole series of keystrokes, but it's not too tricky. The cab controller manual has to be kept handy.


DCC CV Settings for the Class 20 (D8134)
Adr 8134 Long loco address
CV1 3 Default Address
CV2 0 Minimum Speed (V Min at step 1)
CV3 6 Acceleration delay (0-15)
CV4 5 Brake Delay (0-15)
CV5 180 Max speed (V High)
CV6 48 Acceleration Curve (V Mid)
CV17 223 Long address Hi bit
CV18 198 Long address Lo bit
CV29 38 Decoder Configuration

The rest of the CV's are left untouched (factory default).


Running and general impressions

I must say that these locos perform well individually, but excel when used as a pair. I was fascinated to see if one was stronger or faster then the other and I set them together with no load a couple of centimetres apart. I then proceeded in driving them up and down my 6 metre test track. They hardly drifted away from or towards each other. Under a load, the rear loco slows down first and the lead loco then adds it's strength to pull the load. So in that case there is tension between them.

The smallest speed step gets the locos going, but it is so slow that you become impatient to get them moving faster. You can do some precision shunting with these machines.

When running at normal speed, they produce a satisfying hum and gently rock gently over the points. They sit solidly on the track and have not come off during any of my testing manoeuvres.

These locos will integrate comfortably into my mixed steam and early diesel-electric collection. I can see them helping some of the less powerful locos up the ramp to the raised mainline and they will probably be used to prepare the rolling stock for the mainline trains.


 - July 2006

Hopefully we will see another Bachmann Class 20 later this year that will have digital sound built in: D8113 BR Green w/Discs/Tablet Catcher & Snow Plough (D/Sound). Model No 32-040DS. If I can get hold of one, I'll add details of it to this review.

All text, model photos & graphics ©2006 Doug Teggin - All rights reserved.

RSS    Lo-Fi Version Time is now: 12th May 2021 - 22:44