Tuesday, March 28, 2006
Graham Farish Diesel DCC Fitting
Most Graham Farish diesels sold from the early 2000s use two variations on the same Bachmann chassis. This article shows how to fit a DCC decoder to the chassis fitted to the Co-Co locomotives (in particular a class 50), but the procedure for the Bo-Bo chassis is very similar. I’ll detail any differences as I go.
I’ve done Co-Co conversion on classes 37, 47, 50 and 52 (Western). I expect the same chassis is used for classes 40, 44, 45, 46 (Peaks), 55 (Deltic), 56 and 57. The Bo-Bo chassis I’ve converted are classes 31 and 33 (note that the 31 uses the Bo-Bo chassis, rather than the Co-Co). I would expect that the class 25 also uses the same chassis. The 158 and probably other DMU classes also use the same or similar chassis.
Classes 08, 20 and 66 (and any later models except the ‘peak’ classes 44, 45 and 46) use a very different chassis and are not covered by this article.
See the end of the article for extra notes on particular classes.
The Principles
Graham Farish use what is known as a ‘split chassis’. This means that the chassis is split into two halves, each being kept electrically separate from the other. Power from the pick ups is routed through each chassis half to the motor contacts which directly touch each chassis half. As with any DCC conversion we need to break this power route, in this case by milling away some of each chassis half where the motor contacts it. The motor wires from the decoder can then be soldered to the motor contacts. The track power wires get electrical contact with the chassis by being held under the screws which secure the chassis halves together.
The Conversion
Start by removing the body of the locomotive. This is held on by two clips each side of the bodyshell. The easiest method I have found is to hold the loco upright over something soft and slide a fingernail between the body and chassis on each side at one end. Give a little shake and the clips should come apart. You can then either repeat for the other end or gently pull on the undercarriage (be careful not to pull on the bogies). You also need to remove the undercarraige using the small screw underneath (on the Bo-Bo it just pulls off).
Take a look at the chassis from above. Note the black plastic bogie spacers at each end. These are used at the factory to vary the bogie spacing between models. Take a note of which notch on the chassis they are positioned in. Also note which end has the small dimple, since this also varies the bogie spacing.
Now remove the two screws holding the chassis halves together. The chassis should now just pull apart. Remove the plastic spacers (note the one which is positioned underneath the motor for holding the undercarraige in place) and extract the motor.
Each chassis half can now be milled to remove the part that contacts the motor, as shown in the before and after comparison shown above.
(If you’re unsure about milling, or don’t have the tools, a possible work around I’ve used successfully is to superglue a small piece of plastic on the chassis where it contacts the motor, but note that this may lead to increased pressure being applied to the brushed which could wear out faster).
You now need to solder the orange and grey wires to the terminals on the motor. It doesn’t matter which way round the wires go, but make sure they both head upwards from the motor (note that the motor will fit either way up - which direction is upwards is entirely arbitrary). I like to attach the wires to the motor with the motor out of the chassis and later route the wires between the two chassis sections. Others wire the motor in situ and run the wires outside the chassis. It’s entirely up to you, but I feel that with the outside method the wires have to squeeze uncomfortably between the chassis and the body.
You’re now ready to re-assemble. At this stage some people like to apply some insulating tape inside the milled part of the chassis to prevent any accidental electrical contact with the motor.
Pop the chassis spacers back in place. If using the Co-Co chassis I like to swap the spacers over on one end, so that one screw goes in from each side (this makes attaching the track power wires easier), but on the Bo-Bo chassis the screws will only fit one way around. Lay one half of the chassis on it’s side. You can now position the bogie spacers and lay the bogies in place, taking care to put the drive shaft in the motor and the locating pin from the bogie spacer in the hole in the top of the bogie tower. Don’t forget, also, to put the undercarraige mount back in place on the Co-Co chassis.
Attaching the other chassis half can be somewhat fiddly. Lay in on top in the correct position and you’ll probably find it helpful to slightly push the bogies downwards to help the chassis slip over them, but take care that the bogies don’t slip out from the bogie spacers and motor. If you get problems look from the end to check that the bogie spacers and bogie towers are correctly positioned on the chassis halves. With the Bo-Bo chassis the bogie power pick ups contact the underside of the chassis. Take care that they do not get trapped between the two chassis halves.
Once the two halves are together insert the screw or screws which are accessible from that side before turning the chassis over for the other side. When turning the chassis over try to keep it ‘top-down’. If you hold the chassis ‘bottom-down’ the undercarraige mount will probably fall out and you’ll have to start reassembly again (after finding it).
You’re now ready to attach the track power wires of the decoder. This is done by running them under them under heads of the chassis joining screws such that they are held in place when the screws are tightened (For the Bo-Bo one side needs to be secured on one of the plastic securing piece on the other side of the chassis since you can’t reverse the screws. You’ll find it best to tin the ends of the wires before attaching them (tinning means applying a small amount of solder to the bare wires to keep the bare strands together). To make attaching the wires easier, run them around the screws in the appropriate direction so they’ll be ‘pulled in’ as you tighten the screw.
It’s now time to put the complete chassis on the programming track to check all is okay and program in any required settings (including, of course, the decoder address) and give a quick test run on the layout.
The decoder can now be secured in place on it’s self adhesive mound, the function wires can be removed or wrapped in insulating tape ready for later modification (trim them to different lengths first, so they don’t short) and the wires can be held in place on the top of the chassis.
To provide room for the wires on top of the chassis it’s also necessary to file away a small notch on the inside roof of the body, as shown in the photo.
Reattach the undercarraige and put the body back on (note that it will only fit one way around) and everything’s complete.
Notes
Class 158 (and probably the class 170). Before dismantling this model make a note of which way around the bogies are fitted, since they are different at each end. The chassis on this model is very slightly different than described above with two screws holding the undercarraige and two extra plastic lugs inserted between the chassis halves to attach it. It’’s nice to note that these lugs have been redesigned and are less likely to fall out during reassembly. The roof moulding can be removed by inserting a couple of finger nails into the gap between the roof and body and pulling. This will reveal that the body moulding has a solid roof with limited space above the chassis. To create space for the decoder it is necessary to cut a hole in this solid roof. I also recommend cutting the wires as short as is practical since any obstructions in the roofspace will prevent the body from sitting snigly down on the chassis.
See also: Soldering