The Athearn SD40T-2 that I got in 1988 was a locomotive that I wanted sooo bad. I got a snoot nose specially ordered for from the hobby shop. Those were the days when I made everything Chicago & NorthWestern.
I hand painted this thing and bent grab irons with a pliers from piano wire. I did hard wire it back then and coated the exposed metal with the graphite coating called Slip Plate.
The problem with this locomotive is that it's big with a long wheel base. It's notorious for jumping the track on multiple turn outs.
So I was wondering what project to do next when a friend asked if I could do an SD40T-2. I've got several of them and my first thought was to do this rust bucket I got for a couple bucks at the train show. Then I saw my old set of tunnel motors, 1 a snoot the other a regular hood.
When CNW ceased to exist I was in shock and boxed up all my trains where they stayed for 20 years, almost exactly 20 years. I setup a new workshop and promised myself that I would destroy or strip my 72 CNW locomotives, but preserve them. I'm amazed at how detailed these locomotives were. Considering that I had all hand tools and not nearly what I have now, these locomotives look good. They aren't great by today's standard, but they're certainly operating quality.
I spotted my tunnel motors in my lineup of old stuff and decided they needed this rebuild. I remember dreaming about getting this locomotive. I went ahead and did an in depth rebuild.
One of the most important modifications I made was the floating axle. If you're familiar with Athearn locomotives, especially the SDP40 and SD45, then you probably know they tend to derail in yards a lot. The tunnel motors don't just derail they also throw cars off the track. The solution is to make the floating axle.
This rebuild was a total success and the floating axle negotiates multiple #4 turnout with ease now.
So how much pulling power do your locomotives really have? How much more do you get when you add locomotives to get a consist? Are newer locomotives better at pulling?
First things first: why do you want to know? I can answer that for myself and that answer is because no one else is doing it or talking about it.
Practical answer is that when you are planning a steep grade, can you pull your train up that grade? How can you keep statistics that will help you figure out that problem and record the information.
There is a simple tool called a Newton Spring Scale. It's a tube with a spring and a hook that is used in physics to find out how much force is needed to drag objects across a surface or up an incline.
If you're looking at the various scales you buy for a couple bucks, the one you will want to have first is the 5 Newton scale, usually the green one. The next one you want is the 30 Newton scale - you won't use that one a long until you have long trains to test.
In physics you generally hook on to something a drag is across a surface or up an incline and your partner reads the scale and you get a number in Newtons or grams.
On the model railroad, you use a twist tie and attach a dummy coupler to the hook. Then you put a nail or screw in your test track and put the loop at the top of the scale over it so it's laying on the track with the scale visible and the dummy coupler available to attach to a locomotive.
Next, hook on a locomotive and give it some power so it can stretch the scale until it's wheels slip and that will give you a reading you can record. Add more locomotives and start a horsepower chart. Measure them separately and in groups or consists. Reverse their directions and measure again. Rearrange your consists and make more measurements.
You should find that an average locomotive pulls around 1 Newton and more powerful locomotives pull almost 1.5 Newtons. Consider that 1.5 is 50% more power than 1 Newton.
Hook up a train of cars and use the scale to drag them. This tells you how many Newtons are needed to pull that train. Try it again on some grades and watch how much even a light weight train increases the force required dramatically.
We'll get into the conversions to change Newtons to torque and horsepower later. But for your own use, I suggest using and recording the Newton reading directly because it makes things super easy. Just so you know 1 Newton is about .22 pounds.
I made a video demonstrating an Athearn SDP40, GP50 and GP60 on the bench:
I love the AHM C628. Over the years I've obtained about 10 working models and a few more that are in very rough shape, to include one that has a terribly deformed shell from sunlight.
Pretty much everything I say about the C628 will also apply to the GP18, C424 and FP45. They all have the same mechanism. Also, these models were sold as Model Power and Bachmann.
If you got any of these AHM or IHC or Model Power or Bachmann locomotives as a kid or on ebay or at at train show or anywhere else and find that they have broken parts or don't work at all then I have some very good news for you.
There is almost nothing too broken to fix on any of these models. Did you totally crack off and break the motor clips or the couplers?
So I got this C628 and it had all kinds of broken and missing parts. One of the motor clips was gone, the gear towers were missing the small clips that hold the two parts together (those always break off). The couplers were broken off and the side frames wouldn't stay on.
First, sideframes. Don't cut the couple pockets all the way off, leave a little bit so the sideframes stay on. But, since you probably know that after the fact now, you'll need to drill a tiny hole for a 2-56 screw to keep them on. Problem solved.
You've got a huge hole to plug in the front and if you do it the old fashioned way of cutting a pilot out of styrene, which is a lot of work, you still need a platform to screw in the couplers. The first thing I do is take my digital calipers and measure the open pilot and then make an insert on my 3d printer thick enough to screw in couplers. I'm going to go into making pilots in an upcoming post. Quickly, what you do is make a box the size of the opening and thick enough to screw in the couplers and make a 2nd box where you subtract the opening for the couplers. If you've done any design, that will make total sense, if not, believe me when I say that is a 2 move 3d construction that is as simple as they come.
The motor can be replaced easily because it has a standard shaft size meaning that the couplings on the shaft will fit a new motor with no modification. The motor is a 2mm shaft, so take a look on ebay and find the one you like. I personally like the 24 volt motors because I know they won't burn out. Remember that you can go higher voltage than 12 volts, but not lower. 24 is a good number because power packs that have pulse or older high power models can often crank out 20 volts or more which is very hard on 12 volt motors. A 24 volt motor can take the abuse, the only downside is that it will be a bit slower than the 200mph original version you're used to. Something with around 20,000 rpm at 24v will give you about half that much on your layout and will be a little slower than and Athearn Blue Box locomotive.
I like to shave the handrails off these locomotives and replace them with brass wire that I solder in place. Just eyeball the size when you you're at the hobby store. If you're not sure, .032" wire is best to use the first time before you go smaller. Smaller wire is a lot less forgiving.
Shortly there will be a video on youtube that shows each of these fixes. Don't give up on these locomotives no matter what you see under the hood. Even the gears can be replaced if you know what to look for, but gear replacement is a whole other topic.