DCC Loco Conversions - 33 - Dublo Ringfield Motor Bogie Co-Co & Co-Bo

The basic technique is similar to open frame motor steam loco chassis, but the process differs slightly due to the nature of the un-insulated brush holder fitted to the Co-Co and Co-Bo motor bogies being specific to these two locos.

The process for steam loco chassis including source of tools was covered in :-

https://platform1mrc.com/p1mrc/inde...rsions-22-dublo-brush-holder-extraction.6017/

https://platform1mrc.com/p1mrc/inde...sions-23-dublo-brush-holder-replacement.6025/

Although the top housing for the Co-Co and the Co-Bo have the same part number, there is not enough space for the standard length un-insulated brush holder tube in the Co-Co loco due to the bottom edge of the windscreen being in the way. Probably for production economy both locos have the same top housing and shortened tube and cap even though it is not necessary for the Co-Bo.

The un-insulated brush holder on the motor bogies for the Co-Co, and Co-Bo has a flanged end and sits in a recess which is of a larger diameter than is required for the insulated brass tubes that I insert.

1) Extraction - Co-Co and Co-Bo

This is performed in the same way as for the open frame motor steam loco chassis but for the Co-Co and Co-Bo the tube into which the brush holder is drawn needs to be of a larger bore to accommodate its flanged head.

First two Images show the original uninsulated tube in place.





Next image shows the extracted tube and tool.




2) Reaming - Co-Co and Co-Bo

This is trickier than for the steam loco chassis as the bore to be opened out is shallow in depth and recessed into the top housing.

The first and second taper reamers open up the original hole barely large enough for the third reamer to enter making alignment tricky.

The final reamer, the 3/16 inch parallel reamer has limited support so extra care in alignment is required.

Wrapping a few turns of masking tape around the 3/16 inch parallel reamer to take up the difference helps.

Parts of the next stage differs for the Co-Co and Co-Bo.

3) Replacement Insulated Tube - Co-Co and Co-Bo

The new tube was cut accordingly :-

Co-Co length 15mm

Co-Bo length 21mm (standard length)

Engagement of the tube with the shallow depth of the reamed hole allows it to wobble. To overcome this a second layer of 6.4mm heat shrink sleeving is applied to the brass tube so that it is fully supported within the bogie casting.

Co-Co - the outer layer of heatshrink sleeving extends beyond the outer end of the tube but still allows removal of spring and brush when required, commutator end at bottom of image.



Co-Bo - the outer layer of heatshrink sleeving is cut flush with the outer end to allow firm seating of a standard brush plug.

From the commutator end the outer layer starts at approx 6.6mm for both locos.

Check for alignment with a 1/8th inch or 3.2mm twist drill to ensure alignment of replacement tube and the original insulated tube.

Gluing in position is a little tricky depending on the setting speed of the cyano you use, however if the outer insulation sticks too quick all that matters is that there is sufficient insulation for the hole plus a little, the brass tube can be pushed into position within the shrunk sleeving as was the case with one Co-Bo.

If possible get the drill used for alignment in as quick as possible to confirm alignment is maintained while the cyano sets.

The commutator end of the tube is approximately in line with the outer edges of the top housing casting which wraps around the ring magnet as can be seen in the second image.

Skip to (5) in Part 2 for Co-Bo


4) Fitting Specific to Co-Co

The new tube dry fitted.



Clearance forward of the motor bogie in a Co-Co is limited by the closeness of the cab windows.

Fitting a typical brush plug was not possible which is probably why Hornby Dublo used a design where the spring entered the cap so as to be able to use common brushes and springs.

The tube is drilled to accept a nickel silver wire, the diameter is not critical so long as the wire can withstand the the brush spring pushing against it, the top end is bent at a right angle to stop it dropping through.

After drilling and with the nickel silver wire pin inserted.



To improve access and clearance of the pin from adjacent metalwork, the tube will be inserted with the pin set at 45 degrees, this is also the last chance to make sure that the two sets of sleeving around the tube allow it to sit at the correct distance from the commutator.



Cyano glue is applied to the tube and to ensure correct alignment of the new insulated tube a twist drill, nominally 3.2 mm or 1/8 inch diameter (or largest that will fit) was passed through the opposing tube and into it while the cyano glue cures.

Care is required to ensure the correct distance of the tube from the commutator.



New tube fitted.



The pin tail will have the decoder grey wire attached by a hooked solder joint, that will also ensure that the pin cannot be worked loose from the tube in use.

It is important to make sure that the end of the spring bears against the pin. If you inadvertently pass the pin through the helix of the spring and brush rotation occurs, it can drag and rotate the spring too. This will cause the spring if rotated in the right direction to effectively screw itself past the pin until the force on the brush is not enough to power the armature and the motor will stop. This happened to me on initial testing. Please see ref 33.1 for more information on brush rotation.

If you are extremely unlucky the the spring could make contact with bare body or chassis which is at track voltage, potentially destroying the decoder.



Co-Co motor bogie conversion completed.

Continued in Part 2

 

Part 2

5) Fitting Specific to Co-Bo

This stage is simpler for the Co-Bo as the cap arrangement can be replaced by a standard brush plug as used in the factory fitted insulated brush holder.

Cyano glue is applied to the tube and to ensure correct alignment of the new insulated tube a twist drill, nominally 3.2 mm or 1/8 inch diameter (or largest that will fit) was passed through the opposing tube and into it while the cyano glue cures.

Care is required to ensure the correct distance of the tube from the commutator.

The cyano on the outer tube set too quickly for this Co-Bo so the inner brass tube was pushed further towards the commutator, the resulting surplus heat shrink sleeves at the brush plug end were simply trimmed off.





Co-Bo top housing modification completed.

Summary

These motor bogies are slightly more difficult than the open frame steam loco conversions, my two Co-Co and two Co-Bo conversions were successful, the fitting of decoders and wiring for these locos will be dealt with in specific subsequent articles.



References

33.1 Brush Rotation

DCC Loco Conversions - 32 - Dublo & Wrenn Trips & Tips
Part 2 - 20 - Rotating Cylindrical Brushes

https://platform1mrc.com/p1mrc/inde...ns-32-dublo-wrenn-trips-tips.6102/#post-99958


Discussion always

Jim

Return to Index