I have a couple Athearn RTR SD40-2, they are part of the last run they did before their manufacturer went down. It appears that they randomly like to find certain ways for the front wheel of the lead or rear truck to hop off the rail. Has anyone else experienced this problem with this particular model? All my other loco’s run flawlessly over the whole layout but these models seem to be the problem children. The trucks don’t appear to be warped or anything of that nature and everything is in gauge.
Since your other locos run w/o problems, I too would be looking to something wrong w/ these 2. Not familiar w/ the RTR version, but could check the trucks for proper swivel and also slight side yaw. This was a real issue I had w/ the first run of my 2 P2K SD7s. The worm cover “fingers” that provide the tension against the frame to hold the trucks were way too tight. Not allowing any side play of the trucks would cause random derailments wherever the track deviated from any sort of “perfect” level. This may the culprit here as well. Flip the unit over and check axle plane alignment as well as checking for for unobstructed aft rocking and that there is a small amount of side play. I was able to remedy my SD7 trouble by sanding the fingers of the cover to gain some movement. You may be able to do this as Athearn worm covers are quite similar. Don’t file/ sand too much or the entire unit can torque . Allowing one truck to be looser and one tigher will keep the rocking to a minimun or not at all but can allow the wheels to stay on the track. This is the same method used on rolling stock for proper tracking of the trucks.
Just a thought. You will know immediatly as you move the trucks if they are just too tight.
Of coarse if they derail in the same spots all the time, I would double check the trackwork first before tearing into the units.
What other locomotive run ‘flawlessly’ on your layout(manufacturer/model)? What is the radius if your curves(I assume you are HO)?
6 axle engines are not as forgiving as 4 axle or even small wheelbase 6 axle(like SD9’s). I have two Athearn SD40-2 engines from a run about 2-3 years ago(MILW), and they perform fine on our club’s 30" minimum radius curves. Have you taken an NMRA gauge to the wheel sets on these two ‘problem children’? Athearn(and P2K) engine many times have ‘tight’ gauge on the wheel sets. This has been happening even when the ‘Blue Box’ engines were made in the USA. With their long wheelbase, they may be picky of poor trackwork or sharp curves(18"-22" radius). My present home layout has 22" radius curves, and I had to ‘tune up’ a couple of spots in the trackwork when I first ran engines like Athearn SD40-2 and even P2K SD9’s. Even then, they can pull freight cars off on curves. All of my P2K GP7/9’s, Genesis F’s and Atlas RS’s ran with no issue. The new layout to be built this fall will have a minimum of 30" radius curves.
BTW, Athearn has at least two contract builders in China. They have shifted some production and delayed some items due to the shutdown of one of the plants. The ‘warped’ trucks seem to be limited to the Genesis SD70 seres locomotives(SD70MAC/SD70ACe/etc…).
Jim