I took my N Scale Kato NW2 apart to install a drop in decoder and had a "h" of a time getting back together. I made the mistake of taking the fuel tank off which let the whole loco fall apart. I needed five hands to put back together. This probably does not help you with HO but just some input. Not sure if construction is the same for HO.
PC101 To be sure you are starting correctly: The motor's brushes and pickup tabs should be towards the front of loco. (hood end). The saddle has a bar at the top running front to back, that should be on the right side (frame is marked with an ''R'' for right and ''L'' for left). The saddle looks like the right side is more flatter then the left side, picture a ''D'', the rounder side goes in to the left side frame. Add the worms, bearings, joints, bearing retainers and don't forget the insulating bushings. It's been a while since I had a Kato NW2 apart. I can not get my NW2 apart at this time to check the process, I am looking a the drawing. Hopefully you just have the saddle on the motor backwards.
To be sure you are starting correctly: The motor's brushes and pickup tabs should be towards the front of loco. (hood end). The saddle has a bar at the top running front to back, that should be on the right side (frame is marked with an ''R'' for right and ''L'' for left). The saddle looks like the right side is more flatter then the left side, picture a ''D'', the rounder side goes in to the left side frame. Add the worms, bearings, joints, bearing retainers and don't forget the insulating bushings. It's been a while since I had a Kato NW2 apart. I can not get my NW2 apart at this time to check the process, I am looking a the drawing. Hopefully you just have the saddle on the motor backwards.
I believe this is correct. OP, did you take it apart to install a decoder? I took mine apart for a decoder install and it wasn't for the faint of heart. See https://tcsdcc.com/installation/ho-scale/1358 for an example.
Gary
Am having problems in getting the motor saddle to seat properly in the mainframe slots. Is there a simple way of doing this. Thanks