Greetings, I picked up a GP-7 at a yard sale. It's an older Athearn w/ 2 flywheels. It runs really smooth 'n quiet. The only problem is that it's 180 degrees out of sync w/ my other engines ! I removed the shell looking for an easy wire reversal repair... No such luck... Anyone have any experience w/ fixing such a problem? Thanks Mike
I also have a GP7, though it's in phase with my other locos. Without wires to reverse, that's a bit more complicated. Athearns have one pole going through the metal strips to the motor, and the other is in the frame. The only place to change the polarity is in the trucks. One quick fix might be to reverse the trucks, i.e. remove them, and put the front one in the back and vice versa. They will then be reversed in polarity. However, this means dismantling a lot of parts, but it isn't that bad (I did replace the motor on mine, and messed around taking apart stuff, but it wasn't difficult - you just have to keep track of what goes where...).
To reverse the trucks you have to first remove the clip that covers the worm and square bearings. On older locomotives these can become quite fragile so be very careful. The worm shaft with the square bearings will then slide out of the spline in the fly wheel and the truck can be removed. Swap the trucks and replace the parts in reverse of the way they came off. Should fix the problem.
OK, I'm with you guys so far... How difficult is it to remove the trucks from the frame? Do they unscrew or something? Please forgive my ignorance. This will be my first "surgical procedure"
Super easy just read the instructions. The trucks are held inplace by the worm gear cover and spline shafts.
That would be very difficult to do. The motor will only go in one way, the housing is not symmetrical. I suppose the motor could be taken apart and reassembled with the magnets reversed. It is very easy to put together with the trucks reversed. The trucks have different polarity but can easily be mixed up and fit perfectly in the wrong position.
Looking forward to see if the truck switching works. I agree with river_eagle, this sounds like a motor issue instead of the trucks. I have bought many a spare athearn truck set and torn down Athearn locomotives (Blue Box, of course) and never saw any notices about polarity in the trucks. There is no way polarity can change if this locomotive is not hard wired and relies on the standard Athearn Blue Box metal strip method. Averco- are you saying that when you have that GP7 on the rails with other locomotives, it goes one way while the others go another?
The trucks are different from front to back. I just checked a pair out with an ohm meter. On the front truck the bolster plate is common with the left side where the overhead "L" contact strip is common with the right side. The rear truck is the same when mounted on the locomotive but turn it around to the same orientation and it is opposite. Notice the difference in the photo.
Not true. It is not an uncommon problem as there are no labels on the trucks - it is down to whoever disassembles the loco to note where every part comes from. The 'polarity' of the two trucks is not the same. One rail goes to the chassis and the other to the metal strip along the top of the motor, so if the trucks faced the same way then the wheels on the same side of each truck would go to the same contact (chassis or strip). But as they face in opposite directions one is 'wired' the opposite way round.
you're right Russ, even if the motor was in backwards on an Athearn, the polarity wouldn't change. it can only be that the trucks are on the wrong ends.
What you will have to do to fix this problem is take out the motor and reverse the magnets inside. Cant recall how to do it step by step but it is very easy. Take the motor out, take off the top and and bottom clips. You may have to remove the flywheels, not suure. But you need to some how reverse the magnets that are inside to get the polarity the way that you want it. I have done this before. Reversing the trucks will do nothing to help on this.
Reversing the trucks will do it. Believe me, I worked in a hobby shop for years doing repairs and it was always obvious when the trucks were installed wrong. I admit, I made that mistake a few times. We always joked that it would be one way to stage a head on corn field meet without DCC. Although taking the motor apart and moving the magnets top to bottom will work it is much easier to swap the trucks.
Can't you add two wires to the motor? I think for two wires should be enough space. Then you cross these two wires. Wolfgang
Well, you could with some difficulty and it would work. I have had to do that when adding DCC decoders. You have to flatten a sharp tab sticking down from the bottom brush clip that digs into the frame in order to transfer power to the motor. Then you have to use something like Kapton tape to insure the frame is well isolated from the clip. There is enough room between the end of the clip and the front flywheel to solder a wire. However, it is still much easier to swap the trucks front to back. I would bet the reason the locomotive runs backwards in the first place is because the trucks were mixed up when it was reassembled at one point.
Well, reversing the trucks did the job. Now all my engines are in sync (direction wise). Kudos to experience !! Tuvm Mike
