I had posted this in the Lion Chief and other R/C Systems area. I thought it might help some other S gauge folks if posted here also.
I had purchased the American Flyer Polar Express set when it was first announced. After a wait of somewhere beyond two years these finally did show up. I was quite happy with this train and it seemed to be pretty dependable for the most part. After running it for quite a while I started to have problems where the train would stall, it would stop with a loss of power and start up again, without being touched. I attempted to find the problem and it seemed to no avail. I added additional power pick-up to the trailing truck on the engine and that seemed to help a little but the stalling continued to happen periodically. I tried to compare the assembly of this engine to the Nickle Plate engine which I also purchased but did not notice a difference at first. After struggling with this for a couple of weeks. I did a closer comparison of the two engines and did find the discrepancy. The difference was in the assembly of the trailing truck to the engine. The NKP on the stud which runs through the draw-bar and the truck below the cab had one flat washer above the E-clip, where the P.E. had the E-clip above the flat washer. This would cause the binding of this stud on the P.E. and the wheels on the trailing truck to lift from the track and cause loss of power for a short time but long enough to stall the engine. By making the assembly on the P.E. the same as the NKP, moving the flat washer above the E-clip, the binding problem was corrected and power loss was eliminated. I am sharing this because there may well be others whose P.E. locomotive was assembled the same way. I hope this may be of help to some.