I have this Lionel 6-11327 K-4 in because the gear is jumping. I had previously shimmed the gear over as far as possible for the same reason, but the gear was already worn, and obviously that fix didn't last. You can see the gear on the upper side is chewed down, that's where the worm lands. I even slid the motor mount slightly to the bottom by enlarging the holes, but that didn't move it enough to cure the problem.
The "Lionel" fix appears to be the entire drive block for $180 and then move all the stuff over to the new frame. I'm sure this will work, but it's certainly not the cheap way.
Does anyone first know if you could obtain that idler gear, I believe this design is the old K-Line G-4 mechanical design. It's not listed at Lionel, and I suspect they wouldn't have them.
Then comes actually installing it, the drive wheels have to come off to get to the axle ends, and then the gear shaft has to come out (it's behind the wheels).
Am I whistling in the wind? Should I just suck it up and order the drive block?