The Rest of the Story

Just after college, there was an explosion of color on numerous railroads. The C&O already controlled the B&O and so both company’s locos started showing up in the new Chessie System colors of yellow, blue, and vermillion. Wow. The west side of the Huntington shops exploded with repainted units.

As I had only one Chessie loco, a vintage Athearn RTR SD40-2, why not acquire more? Enough of this “bright future” nonsense. I found a pristine P2K SD9 in Chessie; then I found a never-out-of-the-box brother. Wonder if there is another? Yep, to round out my coal drag lash up, and to add variety, another new SD9 in pre-Chessie B&O blue.

And the update begins. Fairly straight forward; old motor, drive shafts, worm gear, and weights out and updated versions in.

Drive Train

In the past upgrades, I have used the Kato motor incorporating hex drive flywheels in all my P2K Es. This required removing obstructions in the frame’s fuel tank area. While the SD9 motor has a smaller footprint, the needed machining in the fuel tank area looked time consuming. Fortunately, late run Athearn RTR motors with hex drive fit like a glove with no machining. All that was needed was to apply a strip of Kapton tape to insure isolation of the motor from the frame.

I also used the newer Athearn worm gears, and on the first SD9, Athearn 90120 hex drive shafts fit perfectly. The last two SD9s incorporate the A-line shafts.

Weight Modifications

The difference in dimensions between the factory motor and the Athearn requires removal of portions of the weight. And as theses 3 locos will be consisted, tractive effort is still more than adequate. Retain the light mounting end pieces which screw into the frame as they make positioning and securing the lights easier. These are the trimmed weight pieces and the factory motor to be discarded.

I cut slots in the frame with a Dremel blade for 0603 smd LED ground lights with copper wire leads. I secured the ground lights with a dab of siliconized acrylic caulk as the thicker modulus captures and holds the light into position more quickly than Kristal Klear (KK).

I used 1206 smd LEDs in warm white and 30 gauge wire for the connections for the front and rear lights secured in place with KK. When the KK is dry, paint the back of the LEDs with black paint to prevent light bleed.

Shown is the Econami PNP board with attached feeds and lights for testing on the first unit. As the speaker will be mounted in the rear, I added length to the light wires to accommodate routing around the speaker. Once satisfied with the positioning, final trims to the wires will clean up the install. The speakers are next.

Speaker Considerations

Space is tight in the rear portion of the frame. While there is more room in the cab area, it produces a sound locality issue. So, rear it is.

I chose a Scale Sound Systems UFIT-MEGA speaker from the Coeval family. The dimensions are 15mm H, 18mm W, and 30mm L. To clear the drive shaft, I added 11mm tall legs from thin sheet styrene. As on other projects, I secured the legs to the speaker with KK. Due to the design of the worm gear retainers, I trimmed the length of the speaker legs to avoid interfering with the truck rotation in curves.

On the SD9 loco shells, there is an itsy bitsy tab in front of the fans projecting down from the roof. Just enough to interfere with the speaker so trim it with a hobby knife (slowly and carefully). I also removed the fans and trimmed the center sprue from each fan to eliminate any contact.

Weathering and Details

I researched Chessie SD9s on several web sites and printed 4 x 6 photos to use as a reference in weathering. Quite a choice available from spic and span clean to grungy and everything in between.

I replaced the rather clunky LL era wipers with etched versions from KV and added cab shades from A-line. Some of the lift rings and been broken as was the antennae so those were replaced, too.

Now if I can just find the little plastic salsa container where I put the couplers and pilots before I moved, I can complete it.

Nice!

I have one of these decorated for DRGW that I picked up at a train show years ago. It runs super smoothly with the stock P2K mechanism (as does my P2K SD45), and I think the level of detail is great, even comparable to modern standards.

I took it apart and noticed the frame had a slight front-to-rear bow in it. I tried to correct this by bending it ever so lightly with nice, even pressure, but unfortunately it promptly snapped right in half!  Fortunately it stays together fine when the weights are screwed back on, so I guess it's OK after all.  I didn't try to add sound, but I did replace the light bulbs with LEDs.

Ouch

Warped frames are a pain and as most are cast metal, they do not accept attempts to force them straight.  Sometimes it can be offset with a little judicious filing at the highest point where the frame curves. The objective would be to allow the shell to fit properly. But in your instance, if the weight makes it functional , call it a win.

I am curious what kind of

I am curious what kind of improvement you saw over the original P2K mechanism.  I have a bunch of them, as it was the Missabe's mainstay of diesels.  They are all stock mechanically, all on ESU Loksound (was stock, then Digitrax, then Soundtraxx, then...) and they work just fine as-is.  On the pair that gets the biggest workout, I had to spin the wheelsets in the lathe, using a small mill file to get the crud off, but that's it for over 20 years of operating. (wow, has it been that long?!?)

Cracked gears

Did the SD9s ever have the cracked gear issue that plagued some of the other Proto units?  

He lost ground

I have observed in tests that the stock P2K motor is an excellent unit, even today.  The current draw is a bit higher than what you get today, but not enough to immediately rule it out.  It’s speed voltage function and torque characteristics make it very desirable.  The Genesis and RTR motors are both poorer in these parameters. Duckdoger indicated that since he was consisting he could lose tractive capability, so he appropriately cut out part of the weight.  This by itself reduced the tractive capability of each unit and the consist.  When you consist, the cumulative current draw level becomes a factor.  Particularly if you have multiple engine consists running in a power district.  Going to the later Athearn motors and dog bone hex shafts did reduce the unit mechanical noise.  So the power loss noise reduction was a good choice for his application.  But may not be right for all.  All in all he has made an excellent set of models using some interesting creativity.

I never experienced any

My impression of the one I

My impression of the one I have is that like other early Protos it's just an update to the standard Athearn mechanism that went off patent. So it has the same gears. I've not had cracked gears in mine yet, but age will get to it eventually.

P2k SD9 gears are more like Kato's

Sound test

Recorded with my iPhone 

Questions and answers, @larry of Z'ville

Thanks for the comments.

This is the 9th P2K re-motoring I have done and a loss of tractive effort has not been an influence on the ability to pull 10 to 12 Proto/BLI passenger cars or 25-ish properly weighted freight  cars. Typical grades in my examples were 2% with minimum 40-inch radius curves.

My motivation was a warning from a model railroad DCC icon regarding the potential of the early P2K motors pulling sufficient current to fry some decoders. Forewarned is forearmed, as it were. I maintain that mindset even though the newer decoders are fat dumb and happy at even 2 amps.

And I prefer the simplicity of the Aline drive shaft to the older, more cumbersome, drive trains. But that is personal opinion.

@mspanton

Thanks for the question Milt.

Using a custom speed table (thank you Chris Palomarez) and a few tweaks in the Bemf CVs, my impression of before and after was smother response in the lower speed steps. And the trimmer lines of the Aline drive shaft affords a little lore room for the Scale Sound Systems speakers.

The added bonus, as suggested by one of our MRH forum mates, is painting the old motors and flywheels flat grey makes a great flatcar load.

@VRS-eric

As noted by others, no issue with cracked gears on the SD9s. Inspected them under a bright light and magnifier during the truck tear down and rebuild. Ix-nay on the cracks.

Cracked gears

Never in the SD9s but I did experience them in a recent project involving a Life Like era GP9. All axle gears were cracked so I purchased the Walthers replacement parts for this locomotive type. Their E-units replacement geared axles are not compatible with the GP style trucks.