As mentioned in the current weekend update I finished this job. Here are the details.
I took on the task of getting this model running again. I was told that the model was constantly shorting out and that when it ran, it didn't run well (possibly due to the way the decoder was installed on one side of the gear tower, forcing it to lean to the other side.
I didn't bother to test run it - I just went ahead and took it apart. The decoder installation could have been one of the reasons it didn't run well. As far as the shorting out goes, It looked like a pair of simulated pipes (brass rods) under the rear of the loco frame were loose and could easily contact the drawbar (which is electrically opposite polarity from the loco's frame).
Since I had the model fully dissembled I also gave it a tune-up. To clean it I immersed all the parts (including the motor) in my ultrasonic cleaner filled with naphtha. I saw plenty of crud that came out of all the parts!
Here is the gear tower taken apart. That is where I discovered a future problem.
Lots of brass shavings! Even with plenty of lubricant present. Both the worm and the worm-gear are made of brass which is not a recommended practice.
The brass-on-brass friction is probably the reason for the extreme wear of the worm gear. Or maybe this loco has a very high mileage. But its driver treads look almost new, so I'm not sure about it having a high mileage. Regardless of the reason, the worm gear doesn't have much life in it. The teeth have been shaved down to a pointy triangular shape. The teeth are worn down so much that pretty soon they will stop meshing with the worm and start jamming. Best solution would be to replace that gear, but I didn't have anything even close to it in my spares box. So I just cleaned and re-lubricated the gear tower.
One nice thing I noticed was how smooth the running gear was. With the gear tower removed I could easily push the loco around without even a hint of any siderod binding. That thing was SMOOTH! One of the smoothest N scale seam loco mechanisms I have ever encountered. I also found it unusual that the driver axle bearings were made of some sort of white metal, not the usual brass. I lubed the axles with light oil and the crank pins and other parts of the valve gear with Woodland Scenics gear lube (as it stays put where it is applied).
Next, I took care of the loose "pipes" on the rear of the fame. I didn't try to solder them back because I feared that other solder joints would let go and I might also damage the paint. So I glued them back to the frame using JB Weld epoxy. Then came the drawbar.
I have no problem using the metal drawbar to conduct electricity between the loco and tender if the drawbar is constructed properly. I used a length of phosphor-bronze wire spring to make a reliable electrical connection between the drawbar and the pin on the tender. Then I also realized that the plastic insulator on the drawbar pivot on the engine side was slightly melted/distorted by heat from a wire being originally soldered to that end of the drawbar (which I removed earlier). I ended up fabricating a plastic washer to fix the problem. I also shortened the spring in the drawbar pivot because I felt it was too stiff, not allowing the drawbar to move smoothly. But even with the spring shortened the electrical contact will remain reliable.
I decided to install working headlights on this model. Fortunately the smokebox front popped off the boiler rather easily. I also unscrewed a cylindrical lead weight from the boiler to get a better view of the inside of the loco.
I drilled a hole in the smokebox front for the headlight wires. I didn't have to drill through the bottom of the headlight as the headlight was not completely cast and the bottom was already open. I had some pre-wired 0402 warm white LEDs (from eBay). I encapsulated the LED in 5-minute epoxy to make sure the exposed leads in the back of the LED would not short to the inside of the headlight, then using more epoxy I glued the LED inside the headlight housing. The warm white color was not "warm" enough for my taste so I tinted the LED with a mixture of Tamiya transparent amber and red paints. That is why the LED has an orange tint when it is not lit. When lit it looks like an incandescent bulb.
The wire leads from the headlight will later be passed to the back of the shell to a pair of contact plates.
As I was repeatedly taking the loco apart and then putting it back together I noticed that the sprung motor mount was jamming against something inside the shell. After some experimentation I determined that the front of the motor and its mount were getting pushed against the front of the firebox. So I ground out the area until the motor was no longer getting jammed against it. The ground out area shows up as bare brass in the photo.
Now to the decoder install: The decoder is TCS Z3 - a very small decoder. I installed the shell, with the smokebox front and the lead weight removed, onto the mechanism. Looking through the front of the boiler it appeared that there was enough room for the decoder mounted over the gear tower. But to be sure I put a roll of modeling clay on top of the gear tower then covered it with some food wrap (so the clay didn't stick to the shell).
Then I firmly put the shell back over the mechanism making sure it was fully seated. After I removed the shell the clay was formed by the inside of the shell. Now I could easily confirm that there was enough clearance on top of the gear tower to install the Z3 decoder. This clay trick comes in very handy when there is no way to see inside the shell with the mechanism installed. The clay takes on the shape of the void which exists between the shell and the mechanism.
The problem with mounting the decoder flat over the gear tower is that the decoder is too wide to fit through the gear tower opening in the bottom of the boiler. I enlarged (ground out) the that opening until it was wide enough clear the decoder. I then touched up the bare brass with Scalecoat II black paint as I don't have any DGLE paint. The DGLE is almost black and the touched-up spots are not really exposed when the model is assembled.
I also had to trim the boiler weight in order for the decoder to fit.
To replace the lead I removed from the weight and to add some extra weight I extended the lead weight using some rolled-up lead sheet. It is simply glued onto the front of the original weight using 5-minute epoxy. I also had to drill a hole in it to clear the screw which attached the boiler to the cylinders.
This photo shows one of the contact plates (made from a piece of copper-clad PC board) glued on the inside wall of the firebox. I also glued in some extra lead on the side of the boiler. The contact plate is polished to a mirror-like shine for good electrical contact. The phosphor-bronze strip which will contact the plate will also be polished.
Once I glued the smokebox front back to the boiler I ran the wires through the boiler and soldered them to the contact plates. The blue tape is temporarily holding the wire until the epoxy glue I dabbed over the wire sets.
I like clean decoder installations without a rats-nests of wires. I also prefer not to have any wires connecting between the shell and the mechanism (for the headlight). I often use custom-etched copper-clad fiberglass-epoxy Printed Circuit (PC) boards to hold components (like resistors) and as interconnects between different parts of the wiring harness. Also, since I was asked to convert the tender to all-wheel pickup (and to install a headlight) I had to add couple of wire jumpers between the loco and the tender. This photo shows all the circuit boards I made, and a wire harness for interconnecting the tender with the loco.
The wire harness utilizes flexible wires and a 2-pin male/female connector cut off from a 50-pin set of 0.050" pin-spacing header and socket set purchased from Digikey. After the wires were soldered to the back of the male connector, I used a dab of 5-minute epoxy to encapsulate the back of the connector. That provides protection against possible shorts and also a strain relief for the wires.
The connection between the shell and the mechanism will be accomplished using a pair springy phosphor-bronze strips on the mechanism and a pair contact plates on the shell. No wires!
I reused the decoder which was originally installed in the loco. But the function wires on that decoder were cut off right at the decoder and I needed them for the headlights. I removed the original clear shrink-wrap sleeve from the decoder, soldered longer wires then used black shrink wrap to re-cover the decoder. I sometimes remove the shrink-wrap sleeves from decoders in some of my decoder installations, but in this case since all the surrounding frame and shell parts are electrically-live brass, using insulating sleeve on a decoder is a good idea.
The above photo shows the decoder and the PC boards installed on the locomotive's mechanism. The decoder is attached using a double-sides carpet tape. That is a thin plastic tape with very aggressive adhesive which should firmly hold the decoder, but it is still removable if needed.
This is a closeup of the previous photo. The circuit board epoxied to the motor holds the current limiting resistors for the headlights and also a phosphor-bronze strip which will contact a metal contact plate glued inside the firebox. That is one of the front headlight connections. The other side of the motor contains the other contact to complete the front headlight circuit.
Also note that I slipped a piece of black tubing over the drawbar. That not only prevents possible shorts to the chassis, it also makes the drawbar less visible.
This photo shows the other side of the model. Again, the PC board on the side of the motor holds the 2nd contact strip for the front headlight.
Closeup of the PC board. This shows how it is utilized to cleanly join multiple wires. It is much easier to solder each wire to a solder pad on the board rather than trying to solder 3 wires floating in mid-air and then try to put a piece of insulating tubing over that junction. Also each separate wire can be easily unsoldered if needed for possible future serving.
This photo also offers a good view of the male part of the tender connector. One wire is used to connect the newly installed right-rail pickups in the tender (while the drawbar conducts electricity from the left-rail pickups) and the other wire is the F0R function for the rear headlight. There is no need for the function common (blue) lead to be connected to the tender. I installed a circuit in the tender which provides the "blue" function common voltage. This way I only need 2 wires to be connected between the loco and the tender.
Now onto the tender: I drilled a hole for the headlight wires through the tender's top and through the headlight housing.Then I again installed a pre-wired 0402 size warm-white LED tinted with some Tamiya transparent paint for an even warmer-white look.
I was asked to convert the tender to all-wheel-pickup using Bachmann tender trucks. These are similar in construction to Kato Mikado tender trucks (except for a much sloppier construction). The wheel gauge on them is also too tight, but if the wheels are spread out to proper gauge the pointy axle ends bind in the sideframe axle cups. If these were Kato wheels where the wheels are press-fit onto half-axles I could simply press the axles inwards slightly using an arbor press. But on the Bachmann wheelsets the axle ends and the wheels are turned from a single piece of brass. To shorten the axle ends I had to turn down the pointy axle ends on a lathe.
The other problem is that the hole for the kingpin in the Bachmann trucks is huge compared with the original brass tender trucks. The easiest thing to do was to keep the original tender kingpin screws and make couple of adapters which would reduce the diameter of the hole in the Bachmann trucks. So I took some measurements, chucked a piece of acrylic rod in the lathe and made couple of adapters.
Here are the competed adapters.
And the adapters installed in the Bachmann trucks.
Next, (on the left of the photo) I prepped the metal pickup/bearing plates. First I trimmed off the tongue (red) and then ground off the plating for the solder joint. I also prepared piece of flexible wire by stripping the ends.
Next step (the middle of the photo) was to tin the bare brass area of the plate and the wire ends. If the plating was not ground off it would have been more difficult to solder than bare brass.
Final step (the right side of the photo) was to solder the tinned wire to the pre-tinned area on the sideframe plate.
Here is a pair of the assembled trucks ready to be attached to the tender.
This is the inside of the tender with everything wired, ready to be closed up. There are holes in the tender floor for the wires coming up from the trucks. I had to grind notches in the cross pieces in the tender's shell to clear the truck wires. The PC board strip glued to the tender floor makes the wiring neater and easier. I also glued in few pieces of lead sheet inside the shell to make the tender a bit heavier for better electrical pickup.
This photo also shows the circuit which provides the "blue wire" (common positive) voltage for the headlight. It is the small black 3-lead component on the large PC board. It contains 2 diodes with their cathodes connected together and to the center lead. The anodes of each diode are then hooked up to leads from each rail. Basically that component acts like a half of a bridge rectifier which every DCC decoder has on-board. Since I only need the positive (blue wire) voltage, I only need the positive half of the bridge rectifier. Using this circuit eliminates the need to run the blue wire between the decoder in the loco and the tender's headlight. The large PC board also holds the 2-pin female connector which is then protruding through an opening I made in front of the tender.
This photo shows the front end of the female connector.
In order to install the 4 screws which hold the tender together, the front wheelset of each truck has to be removed. This is due to the fact that the Bachmann trucks have much chunkier sideframes than the original brass ones. Removing the wheelsets is easy if the metal sideframe plate is lifted on one side of the truck (as shown in the photo). The plate sits fairly loosely in the plastic sideframe and it will come up easily. The wheelset can then be removed, allowing easy access to the screws. I'm not sure why the manufacturer didn't put the screws in a more accessible spot. There is plenty of room inside tender to locate the screws closer to the corners where they could be accessed much easily.
To reinstall the wheelset, first put the pointy axle end in the sideframe plate which is still in the plastic sideframe, then pop the other axle point in the raised sideframe. Then push the raised plastic sideframe down into the plastic sideframe.
Here is the loco coupled to the tender with the wire jumper connected between the loco and the tender. It is in the close-coupled hole on the drawbar. Even in this configuration the loco can freely traverse tight curves.
When connecting tender to the loco the 2-pin connector has to be plugged into the tender first (using tweezers). Then the drawbar has to be hooked onto the pin on the tender floor. In the close-coupled configuration the thick tender wheel axle is in the way of the drawbar and the loco has to be tilted down to be able to slide the drawbar over the axle, then hook it onto the metal pin.
That completes the job - the loco is finished and ready to go back to the original owner.
I did a short test run and the loco runs well. I am planning on giving it a better workout on friend's layout - hopefully later today.
