Con-Cor / Rivarossi N Scale 4-6-2 “Pacific” Decoder Install (Part 2)

In Part 2 of this install, we’ll explore the trickiest problem involved in this install:  connecting power from the tender to the locomotive.

[youtube=http://youtu.be/-s0yAFzUSAc]

Older versions of the Rivarossi 4-6-2 used a plastic drawbar, and only the little spring wire pressing against the drawbar pin in the locomotive to transfer power.  For a DC locomotive, this turned out to be a fairly poor design, but for a DCC install, it makes isolating the tender from the motor pickups easy.

(Un)fortunately, this version of the model uses a metal drawbar, which is much better for ensuring good power transfer under DC, but makes it much trickier to isolate the tender from the motor.

A few options that either I considered or were suggested, which I rejected (and the reasons why):

  • Enlarge the hole in the loco end of the drawbar and put shrink wrap over the drawbar pin.  I was concerned about friction and wear on the shrink wrap, so no.
  • Replace the drawbar with a plastic one.  This would have been an excellent option if I could have disassembled the pin at the tender end.  I couldn’t figure out how without destroying it.
  • Insulate the axle wipers from the bar rivets and wire directly to them.  Again, I was concerned about wear, and I just didn’t have the parts.

In the end, the simplest solution seemed to be to cut the brass bar.  It would have been much easier if I could have removed it from the tender first, but it’s riveted in place, so no.  Instead, I used a drill press to drill up from the bottom where there’s an opening in the plastic, and then cut the rest of the way through the bar with a Dremel tool and a reamer bit.  I did a somewhat messy job of it, but it worked.

Here’s a view of the bottom of the tender before the cut. You can see the opening where I made the cut on the left.
Untitled

Once the cutting was done, I soldered a piece of wire to the bar in the middle of the tender and routed it through the hole to the front near the drawbar. At the drawbar end of the wire, I attached one pin of a NEM651 female connector and shrink-wrapped the connection.

Untitled

Finally, I finished the end of the wire coming from the loco with a single pin of a NEM651 male connector. At that point, we’re done except for buttoning things up and testing her out.

Untitled

I found when testing that with the female socket secured to the tender, it was very difficult to connect up the locomotive on the track. The quarters are very tight between the cab and tender, and I had cut the loco wire just a tad short. By leaving the plug loose, I was able to bring it out of the tender enough that the wires can be connected before the drawbar is hooked up. Much easier, and with everything being black it still looks OK. We’ll see what the customer thinks. I hope he likes it.

 

Con-Cor / Rivarossi N scale 4-6-2 “Pacific” Decoder Install (Part I)

I was recently asked by a friend to install a decoder in an N scale Con-Cor / Rivarossi 4-6-2 “Pacific” locomotive. It seems that install instructions for this model are scarce, so I will share how I managed.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2
(shown with the steam-dome shell screw partially removed)

This locomotive model has an odd (really, just old) method of pickup. The fireman’s side (left, going forward) rail is picked up through the drivers, while the engineer’s side (right, going forward) is picked up through the tender. Power is transferred from the tender to the engine through the drawbar and a stiff bit of spring-wire that contacts a peg sticking down below the cab.

This is actually the trickiest part of the install. The drawbar peg on the engine is directly connected to the lower motor brush, and the drawbar itself is conductive. So in order to isolate the motor from the rails, you have to somehow insulate the drawbar and provide an alternate path for the tender pickup to the decoder. More on that later.

For this install we chose the Digitrax DZ126T as the best balance between cost and size. The TCS Z2 (also a good choice) is slightly smaller but more expensive. The Lenz LE077XF is only a little more expensive than the Digitrax, but is the largest of the three. Any of these would work, though, and would follow the same basic install process.

The first step is to locate a good spot to fit the decoder, and do any necessary milling or other modifications to make room. Another install page showed installing the Lenz decoder under the cab roof, after some milling to the inside of the roof and to the top of the frame. On looking at the frame design, I decided to fit the decoder into the boiler where the upper headlamp contact is. There is room for the DZ126T at that location without any frame modifications.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Remove the shell by taking out the screw in the top of the steam dome on the boiler and then spreading the firebox sides slightly. It is a tight fit, but with some shaking the frame will drop out. Next, remove the two headlamp contacts from the center of the frame and disconnect the black wire running from the upper contact to the rear of the locomotive. Keep the lower contact. You will need it later. Also remove and keep the spade lug on the back end of the black wire. The upper contact and the wire itself can be discarded.

Next, I test-fit a pre-wired T1 white LED that I had handy. It fits nicely into the brass slug that previously held the headlamp. I went ahead and used this pre-wired model, but next time I would probably custom build a T1 LED and resistor to make it as compact as possible and make a little bit more room for the decoder. The shrink wrap on this LED assembly got in the way.
DCC decoder install in a Con-Cor/Rivarossi 4-6-2
Pre-wired T1 LED in the boiler

DCC decoder install in a Con-Cor/Rivarossi 4-6-2
Test fit of the pre-wired LED

After test fitting, I trimmed the LED assembly as short as I could and wired it to the decoder. The decoder Blue wire (common +) goes to the current limit resistor (connected to the LED’s anode) (red wire) and the white wire (forward headlight function) goes to the cathode.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

The upper brush contact of the motor contacts the frame through a brass spade lug. We must remove that lug, turn it around to face away from the frame, and attach the decoder grey wire to it.

To remove the motor, you must first remove the lower brush contact. Pull straight down on the white plastic ring around the tender pin until it comes loose. Be very careful. It is a tight fit, and when it comes loose it is likely to fly off, taking the spring and motor brush with it.

Next, pull the motor out of the frame by pulling (or pushing) straight back firmly but gently. Remove the spade lug tab from the top motor contact and solder it to the grey decoder wire. Solder the spade lug removed from the lighting tab wire to the orange decoder wire.

After measuring for proper length of the grey and orange wires (they’ll reach back from the decoder position over the top of the frame), I cut and soldered the wires to the spade lugs away from the loco to prevent overheating the motor brushes.

Aesthetically, it would be better to solder the grey wire to the bottom contact and the orange wire to the top contact, so the orange wire is hidden from view. This would make the motor run in reverse, but that can be corrected by programming the decoder.

I lined the inside of the back of the motor mount hole in the frame with Kapton tape to ensure no contact between the brushes and the frame. This might have been overkill but I wanted to be extra-safe.

Reinstall the motor in the frame and reinstall the lower brush contact and tender pin. Slip the spade lugs back onto the motor brush contacts with the tab pointing back away from the frame.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Once the motor is back in place, bend both spade lugs flush with the back of the motor.

Now, we’re almost done.

Cut and solder the red decoder wire to the lower headlamp tab and re-insert the tab into the frame. Secure the decoder to the top of the frame where the upper headlamp tab used to be. Tuck and secure all of the wires. The black wire should run back along the Engineer’s side of the frame where the black headlamp wire used to be, and will stick out the back of the cab for some length. The yellow wire can be cut short and tucked.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Bend the red wire tab up a little past vertical. This will ensure the red wire is not sticking down where it can be seen when the shell is re-installed.

Slip the headlamp into the hole in the boiler slug, then carefully reinstall the shell. It is a tight fit, so you may have to do some “encouraging” to get everything in. It helps to take a small screwdriver and tuck the black wire under the lower edge of the boiler to hide it, much the way one would tuck a cable beneath the baseboard of a house wall. Be careful not to damage anything.

At this point, you should have a complete, running locomotive, except the black wire is sticking a few inches out the back of the cab. To test the locomotive, use an alligator-clip test lead to connect the black wire to the engineer’s side rail of your test track. The locomotive should power up, respond to DCC commands, and run (at least as far as the test lead will reach).

Now is the time to fix anything that is wrong.

In the next installment, we will see how to connect the black wire to the tender and complete the installation.

Having the Right Tools

Wow. I only just realized that my mobile app hasn’t actually been publishing any of the posts I’ve been writing. So I’m a little bit behind.

Anyway, tonight’s thoughts revolve around having the right tools. A week or two ago I had to assemble a couple of circuit boards. Tiny SMT stuff. I have a good soldering iron, but the tip was a bit large. Some old goopy rosin flux, and a couple of really cheap tweezers. Let me just say, it was not a pleasant experience.

Tonight, it was time to build a few more. Fortunately, this time I had a new, smaller tip for the iron, some high quality no-clean solder flux paste, and a pair of high precision curved-tip tweezers.

It was a breeze!

Another version of the same story… I’ve spent years trying to hack together carpentry jobs using a jig saw and a hand-held circular saw. Not so good. Fine for rough carpentry, but not for display-quality stuff like a nice model railroad shelf.

Enter the table saw. Clean, accurate cuts, made quickly.

Now, the table saw was a large investment. I’m not really here to advocate spending a pile of money. But the tweezers, flux paste and iron tips were a total investment of about $10.

The right tools are worth their weight in gold, but they don’t have to cost a fortune. Don’t waste your hard earned dollars on cheap tools.