Thanks for taking the time to reply. I finally had a day off work with nobody else home so I was able to spend a little extra time with my trains and did some work to resolve this problem.
First, I measured the wheel width/gauge on my troublesome Williams E7 against my other engines and several cars. As it turns out, the E7 is pretty much smack in the middle of the variances I found - not too narrow and not too wide.
Next, I postulated that there was an excessive amount of side-to-side play in the leading wheel+axle set on the trucks (over 1/8" - much more than any others I had). I filled the gap with a few 1/4" e-clips on the axles between the wheels and the mount to reduce the side play without binding the wheels. Unfortunately, that was a dead-end. I also looked at the truck pivot point as a problem area (not in the middle, actually behind the middle axle) but that led nowhere as well.
I then removed the leading truck from the E7 dummy unit and ran it around my layout behind my Lionel 4-6-2 Pacific. Even without the body the truck routinely derailed while being both pulled and pushed thru the O-36 FasTrack switches. At least now I was able to determine the cause...
The E7's six-wheeled trucks are very long, and Williams chose to install a flanged wheel set on the leading axle (unpowered), an un-flanged wheel set on the middle axle (powered), and a flanged wheel set on the rear axle (powered). This puts the flanged wheels at the furthest distance apart. Just pushing this truck thru an O-36 curve reveals that it is tight; I don't know how it would get thru an O-31 that Williams advertised. There is so much lateral binding on a curve that the leading outboard wheel is literally pushed up and over the outside switch rail.
Unfortunately, the O-36 switches are just as much to blame. Each switch rail comes to knife edge and rests against the main rail depending on which way the switch is set. In this case, Lionel produced these switch rails with a taper along the top edge as well so the switch rail does not come to the same height as the main rail it rests against when it is thrown over. Combine this with the excessive lateral forces caused by the flanged wheel sets being so far apart and it is a forgone conclusion that the outboard wheel will ride up and over the switch rail causing a derailment at any speed above dead slow.
Sorry for the long-winded explanation, but I think I may have a solution.
In order to reduce the amount of lateral binding on an O-36 curve, I propose to move the unflanged wheels from the middle axle to the trailing axle, and move the flanged wheels from the trailing axle to the middle (with the reverse set up for the rear truck). This will put the flanged wheels much closer together and allow the E7 to negotiate the curve with less lateral binding. With luck, this will also help keep the leading wheels from riding up and over the switch rails.
The final result would be that the first two axles on the front truck would have flanged wheels and the last axle would have unflanged wheels. On the rear truck it would be the opposite. The only other option is to swap the wheels between the first and second axles leaving the front axle with unflanged wheels, but I believe this may cause it's own problems through the switches.
Unfortunately I do not have the necessary tools to perform this work (wheel puller and a press) and since I'm new to the hobby I've not made any connections locally as of yet. I'm hoping that someone out there can try it out on one of their units and let us all know if it works.
Cheers - Jon651
