1991 production Axial-Flows had a noticeable change. The words "Axial-Flow" were at the top of the cab, replacing the "CaseIH" emblem between the cab lights. Actually this served another purpose besides decoration. The area underneath it was redesigned so as to discourage birds from building nests in the windshield wiper motor area, a common complaint on earlier 1600 series Axial-Flows. The belt which ran the hydraulic pump was changed to a double V-groove belt for better reliability. The 1660 also received the different hydraulic reservoir/filter setup that the 1680 had received the year before. The unloader auger drive was changed from an open set of gears to an fully-enclosed, oil bath gearcase. More operators were "unloading on the go" and the open-gear unloader drive was experiencing more problems, especially in high-moisture corn. Also, the augers were spline-driven to and from the upper gearbox, instead of being fastened to the gearbox on previous models. The 1680 had 2 "elephant ears" removed from its rotor impeller, using just 2 instead of 4, for greater capacity in tough-feeding crops.{(***---------- CaseIH had also experienced engine failures on earlier Cummins engines used in the Axial-Flows. The original piston design did not have a "nickel-insert" around the #2 piston ring, causing the ring land area to break, causing major engine damage. CaseIH instituted a upgrade program to replace all the sleeves and pistons on affected units, replacing the pistons with a new, improved design that had a "nickel-insert" around the #2 ring land.-------***)} CDC/Cummins also came out with various engine changes that allowed better oil temperature regulation and better filtration, which resulted in a new-design engine oil filter which bypassed a portion of the oil through a "super fine" portion of the oil filter. Also in 1991, production of 3 models of Axial-Flows ceased. The 1620 self-propelled, 1670 hillside self-propelled, and 1682 pull-type combines were discontinued due to declining sales numbers; leaving just the 1640, 1660, and 1680 self-propelled models to "carry on" the Axial-Flow banner.
-read about that in the axial flow section of "toy tractor times"