Abstract: An idler shaft assembly is disclosed suitable for internal combustion engines, such as the heavy duty engines. The assembly may transmit power between a crank shaft and a cam shaft. The assembly includes a hollow shaft which can be interference fit within a small idler gear, with a large idler being mounted on a shoulder of the small idler gear. Idler hubs on either side of the hollow shaft are centered with respect to the idler shaft and are held firmly in place by fasteners that extend through one of the hubs and the hollow shaft, and are threaded into the other hub. Lubrication may be provided by an internal reservoir formed in the hollow shaft, and oil passages in fluid communication with this reservoir that extend to journal bearings mounted between the idler hubs and the support structure for the overall assembly.