The main reason they don't recomend the AFX rotor in a 14_1660 (as well as the pre'91 14_1680s) is they had the "short cleaning sytem" In '91 they came out with the "long" cleaning system in the 1680s and in '93 with the cross flow cleaning fan. Check over on www.redpowerforum 's "coffee shop" there is a discussion going on right now about this topic. Check out j.p.'s posts, he is a combine test engineer for CIH and has lot's of experience running the AFX rotors in several different crops and lots of conditions.