The other engine I alluded to in my post regarding the 2026 is a Lionel 646. The 4 wheel rear truck is very loose and floppy to the point that it will not stay on the track. I noticed some type of connector in the front part of the truck but it is not a screw nor does it have a screw head. I thought it could be turned down to tighten the truck to the loco's body but it will rotate only. Perhaps the shell has to be removed to tightening it from above?
Once again, I defer to the members of the forum for advice and insights. Thank you.