There are a few things to note when seeking out imported HO diesels, cheifly those offered by Life- Like, ATT , Charmerz, AHM, IHC, Varney and Model Power.

  First there are the "big motor' units, These have a large vertically mounted motor over the rear truck driving the rear wheels only. The oldest of these used a 5 pole motor, metal gears, brass axles, and current collection from both trucks, and have the deep flanged "NEM" wheels.Later production used a 3 pole motor and plastic gears with plastic axles, current collection from front truck only and eventually changed to smaller flange "RP25" wheels.Built by Mehanotehnika in Yugoslavia starting in 1960,. These brutes are great fun and will generally always run, even if in poor condition, due to their sturdy construction.Models you will find with this drive include the FM C-Liner , MDT and BL2 by AHM, ATT FT Diesel, Charmerz FA 2,and the Old Life-Like F7 among others.

  The next are the "small motor" Diesels, which interestingly are all modeled after ALCO prototypes. These used vertical 3 pole motor of smaller size, driving the rear wheels only, current collection from only the front truck, and headlight in long hood end, initially built with deep flange "NEM" wheels, later changed to "RP25" wheels. Production of these started about 1964 and included the Varney RS11, ATT Alco 415 and MDT, and the AHM RS-2 and ALCO 1000 (S2). these can be a little touchy and are subject motor heating. Pure DC power packs are a must because transistor packs will burn the motors out.

  Starting in the mid 1970's models began to appear having a totally new mechanism with a flat can motor connected by driveshafts to modular geared trucks, powering  4 or more wheels depending on the model.These were offered in many models,and during production some earlier models were revised to use this drive, some of these may still be available.The only weakness in this design is the brush springs which can fail due to motor heating, fairly common in models that have been stored for long periods.All of these are equipped with RP25 wheels.Models using this drive include the AHM C 424, GP18, SW1, SD40, FP45,Center cab switcher,35 ton, late production RS 2, Late ALCO 1000, Very late FM C-Liner (1980's), Model Power RS2, Life Like C 415 and RS11, Charmerz FP45 and Life Like C628 to name a few.

  It might be interesting to note that all of these locomotives built from 1960 to present used the same nickel plated wheels whether they were small or large flange.This is by no means a complete list, but information I have gathered through personal experience and research over the 35 plus years that I have been collecting and repairing these wonderful trains, You wil find some variations in model runs of some of these.HAPPY HUNTING!