Lionel 18034 Mikado sluggish and jerky especially in reverse

The later ones don't have a bearing/bushing in the top.

Is the motor loose in its mounts? Is the driven worm gear on the axle still tight on the axle?

There is an Allen screw on the bottom of the chassis which is supposed to adjust the alignment of the worm gears. If, and only if, the motor and the geared axle both have good bearings, this adjustment might help.

Somewhere in the Kughn era, the manufacturing engineers loosened the tolerances, and/or the production folks put in the wrong bearings, and the armature winders cheapened up that part, too.

The end result turned what was arguably one of the most solid postwar designs into a POS, in my opinion. The Rock Island was the most infamous of these.

It didn't have to happen, but it did. Another corporate idea gone bad. I lived through a lot of them in my "career."

That's a bit untrue in my experience, since the 18007 Southern Pacific GS-2 and the 18022 Pere Marquette Berk Lionel did ran perfectly.

Thanks for the help.  The motor appears correctly mounted and will turn the wheels freely for most of the rotation.  I couldn't find an Allen screw on the bottom of my engine or any other screw near the motor. 

So, I ran it forward and reverse for a few minutes with the shell off to see if it would work itself out.  It did not, so I removed the motor and shell and turned the wheels by hand forward and reverse.  In both directions there is a bind at the 10 o'clock position every time.  In that bind location, all the linkage jiggles freely and the three sets of wheels in the rear will jiggle forward and reverse freely.  The bind appears to be the front set of wheels.  In addition, the rear three sets of wheels will move freely left to right a very slight bit.  The front set of wheels don't move freely left to right, they kind of snap back and forth (but about the same amount as the others).  Gunrunnerjohn suggested I check the smoke linkage and measure the distance between the wheels.  So that's where I am headed next.  Having run this engine a little bit now I am beginning to see a wear line on the wheels and the rollers, so I can't believe this has ever been run before.  In fact, if the engine stops on the track in the bind position, a postwar ZW at full voltage cannot get it to move.  You must hand assist to get it started. 

Any more help will be greatly appreciated.  I didn't keep any postwar 736 engines that I can find to check them, but I remember them being very smooth engines when I had them.  The MPC FARR engines I used to run were very smooth also.  I really like the appearance of this engine and would like to get it running.  Thanks again.

One thing I have found that could cause a bind is that the valve linkage hangers, which mount to the frame, could be bend downward enough to contact the side rod or the main rod. A good idea wound be to remove all of the linkage, and if that removes the bind, add one part at a time until the bind returns. I would bet that the main rod is touching the valve hanger some where, just enough to make the loco balky. Keep us posted.