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Locomotive Intensive Care Unit

The GNRR maintenance crew discuss their repair options for GNRR locomotive #4125, and it’s not looking good.

When I was taking photos of locomotive #4125, a Walthers Proto2000 GP20, I noticed that the frame appeared to be bent up on each end of the locomotive. The front end was much worse than the rear, and the bend caused the front coupler to be approximately ½ a coupler too high on the Kadee coupler gauge. I figured that the shell was not seated properly on the frame causing the issue, or something else was wrong with the frame.

I decided I had two options, one was to ignore the issue and just use the rear coupler on the locomotive, or the second was to send it to the “locomotive hospital” (my workbench) for a checkup to see if I could fix the problem. The first option did not really work for me as the locomotive coupled to cars on each end during switching operations. I decided to choose the second option, and see what the problem was, and if I could fix it. I removed the couplers after applying a little pressure to the frame to get them to slide out of the coupler slot in the shell. I removed the shell and noticed the frame was bent up on each end, and the front end on one side near the hole where the truck mounts had a small crack. That’s not good I thought. Maybe if I try to straighten very carefully and apply a little epoxy to the crack that will fix it. I applied very slight pressure to the frame to push it back to level and it broke into several pieces. OK, now I have a real problem! The more I touched the frame the more of it just crumbled into pieces, ultimately the entire front of the frame broke off including the mounting pin for the front truck. This locomotive now needs the Intensive Care Unit, not just the regular hospital to fix it!

I did not want to get rid of the locomotive since I had spent many hours custom painting it, adding ditch lights, and upgrading the decoder to an ESU LokSound. I decided to contact Walthers to see if they had any replacement frames for the GP20 and described the issue to them. I was contacted by one of their repair staff and told that they don’t have any replacement parts, but they might have a returned unit that they could scavenge a frame from since the locomotive had not seen many changes since the original production. The repair person also informed me that “zinc pest” was a problem with those specific units and caused the frames to crack easily due to impurities in the casting process. They repaired many of the original units under the one year warranty and had run out of replace frames, but it was not covered after that as it is consider similar to rust. A few days later I got an email indicating they found a GP20 frame and could send it to me for less than $40 including shipping. Sold!

In this photos the repair process has begun, note the broken frame with the motor still attached and the new replacement frame below. I also made notes of where each wire was connected on the decoder. Don't trust your memory to prevent frying a decoder.

Now the fun part, installing the frame in a completely assembled and detailed locomotive unit. Replacing a frame in a locomotive is similar to replacing the foundation of your house while you are living in it. It is a lot of work. I was able to remove the trucks after un-soldering the pickup wires from the decoder to each truck. I also had to un-solder the motor wires from the decoder. I got lucky that I was able to leave the wires to all the lights connected to the decoder, and then removed the weight from the original frame with the decoder attached to it. While the frame was exactly the same as the old one, the screw holes were different sizes and depths. The original screws had to be shortened or changed to the correct sized ones. Once I got all the parts back in the right place I installed the weight on the new frame. Of course while reinstalling it a few of the light wires broke off the soldering pads for the decoder. I was able to re-solder the light wires, then soldered the truck pickup wires and the motor wires to the decoder. Prior to closing up the locomotive I tested it to make sure everything worked. Success, everything worked perfectly!

This time I made sure that the shell fit properly on the frame and then reinstalled the couplers. The locomotive is now back in service and earning its keep working the line. The photo above shows the locomotive departing Tate Yard with a string of loaded open top hopper cars enroute to Marietta.

I think the main cause of the bent/broken frame issue was that I forced the shell onto the frame, but something was not allowing it to seat properly. When I pushed the frame up slightly to install the couplers, that’s when it broke due to the original manufacturing defect. The lesson learned is to make sure the shell fits correctly and don’t force the frame to make it fit, even if it is make from metal. With a little time, patience, and some luck you can usually fix most problems with a car or locomotive.

Until next time, stay safe and keep model railroading.

623 views4 comments


Kudos to Walthers for extricating a usable frame for the repair. Saved you an e-bay search for a used unit. Did you take the opportunity to conduct some maintenance on the trucks to check the gears and lube the bearings? Your videos always show such ultra-smooth loco operation, especially when coupling. Love those safety stops.

Thomas Klimoski
Thomas Klimoski
Jun 20, 2021
Replying to

Hi Rogert, I really appreciated the Walthers repair department helping me out with finding a frame to use. I did check the gears and bearings and everything looked good. Thanks for your comments on my operations. -Tom


Alex Bogaski
Alex Bogaski
Jun 19, 2021

Great post, Tom. I admire your patience and attention to detail. Hope it runs well from here on out!


Wow. You have much more patience then I, my friend.

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