Pictures and text by Robert Lewis of Tilehust, Reading, United Kingdom
This is a Wrenn locomotive of the City/Duchess Class of the LMS, it is a
evolution of the original Hornby-Dublo 3 rail locomotive. The Wrenn model being
of 2 rail type, with the wheels being isolated from each other (left & right
side, unlike the 3 rail version), but this still leaves the metal chassis being
live, directly connected to the left hand wheel set through the axles.
Picture Wrenn-1 To remove the body, un-screw the retaining screw located above the front pony truck.
Picture Wrenn-2 & 3 * Important * , Both motor brush sleeves must be isolated from the metal chassis. The brush holder (2) is factory fitted within an insulating sleeve. This arrangement has to be replicated with the other brush sleeve (3). This can be achieved by purchasing an insulating sleeve from one of the many Wrenn spare suppliers in the UK. The component parts can be seen in picture 3, the insulating sleeve being the darker one.
To begin, remove the rear pony truck, the permanent magnet and the metal poles. Release the brass locknut and unscrew the top motor bearing, the commutator can now be removed. The existing brush sleeve has to be removed, this can be done by passing a fine square ended punch through the insulated brush sleeve, and locating it on the edge of the un insulated sleeve, a few gentle taps with a hammer will push it through. the hole in the chassis has to be opened out to the match the outer diameter of the new insulating sleeve, this can be done with a drill or reamer. Care must be taken to ensure the hole remains in line with the opposite brush sleeve. The new insulating sleeve can now be inserted, I placed a small drop of super glue (Cyanoacrylate) on the sleeve to ensure it remained in place. The original metal sleeve can then be inserted, ensuring there will be clearance between it and the commutator. Just to ensure insulation I used some transformer tape (yellow) on the exposed end of the metal sleeve. ensure to clean all swarf (filings) from the metal chassis, then reassemble the commutator and bearing, magnet and pony truck.
Connect the red decoder wire to the solder tag (1) and the black to the wheel pick up wire (2). connect the grey wire to the front brush cap and the orange to the rear.
Test the installation before replacing the body. If all is ok the wires can be held in place with hot glue, I mounted the decoder vertically on its long side using hot glue in the area in front of the solder tag. Replace the body and securing screw.
While the locomotive was apart I also replaced the magnet with one of the Super Neo Magnets now available, it was a big improvement compared to the original steel magnet, which had lost most of its magnetism due to its age.
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