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Hornby R2204

BR 4-6-2 Merchant Navy Class 'Bibby Line', 35020 

Review & DCC Decoder installation - Text & photos by Doug Teggin



Prototype Info:  

Built at the Eastleigh works in 1945, 'Bibby Line' was rebuilt in 1956 and withdrawn in the early months of 1965. It is unfortunate that this locomotive has the dubious record of being the only member of the class to be cut up by BR.

Class Introduced: 1956; Loco Weight: 97tons 18cwt; Driving Wheels: 6ft 2in. 


Length: 290mm; Running number: 35020 'Bibby Line'; Livery: BR green (early emblem); Period: Mid 1950s; Features: Sprung buffers; Finish: Pristine; Motor: 5 pole skew wound loco drive; Purpose: Heavy express passenger; Suitable rolling stock: Pullman cars, R4057, R4115, R4114, R4116, R4117, R4125, R4124.


Metal buffer on the front of the loco along with some optional accessories (ladders and pipes). The cab is not as detailed as the A4 or the Q1, but it's ok. It's lack of detail won't distract from the overall appeal of the loco.
The tender is nicely detailed. Ladders, sprung metal buffers and pipe work make it even more interesting. The brake rods under the tender are supplied as optional accessories.

DCC Decoder Installation

Follow the supplied instructions to take the loco apart. One screw under the front bogy and a couple of clips under the cab and you're done. You don't have to force anything - if you do it right, it comes apart easily.

I installed a Arnold Digital 81201 decoder into the Loco. As there are no extra functions required by the locomotive a simple, but robust decoder is fine. The 81201 can handle 1.5 amp. The Merchant Navy Class 'Bibby Line' model draws 0.15 amp when rolling by itself; 0.35 amp when held stationary at the buffers, but with wheels freely sliding on the track. The locomotive (with tender) can pull 1.42 kg (6 x 150g coaches + 4 x 130g coaches).

The installation was a little bit tricky, not as easy as the previous two installations due to the lack of NEM 652 (NMRA Medium) socket and more importantly: a lack of internal space for the DCC decoder. Where installing a DCC decoder in a loco that has a NEM socket may take about 10 minutes, this installation takes over an hour because you have to do some trial fitting and adjustments.

Note: The TV interference suppression capacitor has to be removed for DCC use. A capacitor is only needed for conventional operations to prevent radio interference. With DCC operation a capacitor corrupts the data format and the error free data transfer is disturbed. A snip with a small cutter does the job. I removed the capacitor and exposed all the wires (below left).

Cut off the NEM Plug from the decoder if it has one and following the wiring diagram, attach it to the pickup wires and motor terminals. The red decoder wire is attached to the wire from the right wheels on the loco and the wire from the pin connector of the tender (lower copper brushes on the tender hook of the loco). The black decoder wire going to the left wheels on the loco and tender. The orange decoder wire goes to the lower motor terminal; the grey decoder wire going to the upper motor terminal.

The DCC chip sits attached to the inside of the boiler roof  directly above the gearbox in front of the motor. It is cramped in there so you have to tape down the wires to prevent them jamming the chassis when it goes back into the body. A few layers of double-sided tape keeps the decoder secure. Tape everything in place with black electrical tape and close up the body.

Note: This locomotive does not have lights so the function wires are not used.


DCC CV Settings for the Merchant Navy Class Locomotive
CV1 20 Address (The loco number)
CV2 2 Minimum Speed (V Min at step 1)
CV3 4 Acceleration delay (0-15)
CV4 4 Brake Delay (0-15)
CV5 180 Max speed (V High)
CV6 50 Acceleration Curve (V Mid)
CV9 216 PWM frequency (69Hz)
CV29 2 Decoder Configuration
CV49 0 Decoder specific values
CV50 20 Decoder regulation

The rest of the CV's are left untouched (factory default).
Note: One big issue with the latest Hornby models that use this system to transfer electrical current from the tender to the locomotive via copper brushes on the tender hook. The tender hook itself is conductive, then there is a plastic ring insulating it from a plate above. The tender hook feeds current from the right tender wheels and the plate feeds current from the left tender wheels. Sometimes the brushes on the loco that are meant to touch the plate, get jammed on the plastic insulating ring and end up in contact with the tender pin (see upper left photo). This causes a short-circuit and shutdown of the DCC control system. When attaching the tender to the loco, make sure the brushes are in the right place before turning on the power. Photo upper right: A: Left wheels brush from loco are correctly touching the plate on tender; B: Plastic ring where brush can catch causing a short-circuit; C: Right wheels brush from loco touching the tender pin; D: The length of the tender pin that is conductive.


A very attractive model. Beautifully made with the good detail. The locomotive runs very smoothly. Under DCC control, it moves off on the first speed step, without any jitter or hesitation. It will look good on a classic layout hauling a rake of coaches or a collection of heavy goods vehicles.


 - April 2005


All text, photos & graphics 2005 Doug Teggin - All rights reserved.

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