Athearn Blue Box S12 HO switcher is used as a mechanism for the S scale DH locomotive. Most Athearn Blue Box switcher locomotives, with plastic side frames/inside bearings, used the same base mechanism. With a few minor modifications it makes a suitable drive unit.
Main changes are:
1. File down the fuel tank, with a course file, to fit between the DH tanks (25mm wide).
2. Lengthen the frame by 4mm to get correct length between bogies.
3. Move front flywheel, motor brush end, forward on shaft by about 3mm.
4. Fit North Yard 42inch S scale driving wheels (14.3mm diameter), part number 480N x 8.
5. Shim the frame so the body sits at correct height. (0.5mm under bogie pivots and 0.75mm on locomotive frame)
The wheelbase of the bogies is still a bit short, but behind some suitable side
frames they should look okay.
Follow the link below to view the changes made to the mech's frame: