Sorry I cant help ya with the corn but I just installed a full set of Gorden bars and helical concaves in my 1680 and only had a chance to run for a few minutes today in tall fescue grass seed. But, I will tell you that in the grass, what little I've had the chance to run, the bars and concaves appear to really be the ticket. Once the order showed up and I could see the concaves and bars together on the shop floor, the theories behind them started to make really good sense. In my opinion, so far, the best way to get the most good out of the Gorden bars is to run them with the helical concaves, and vise verse. The cross bars on the helical concaves are just about the same angle as the gorden rotor bars. It appears to give you a true 90 degree thresh action to the crop flow. When I shut the machine down full and looked, thats exactly what I saw. I was very impressed with the movement of the material through the machine. Usually with the tough straw the material will stall and rope. Not so with the Gorden setup, the material moves smoothely. But, this is just the first short little observation I've had the chance to make in tall fescue. I hope to get back into the field maybe sunday, and do more experimenting and observing.
