you can run a rotor PD slow and still shell corn, 88 series can run even slower than a 66 because of the larger diameter. too wide of concave setting will tend to hair over the concaves with green material and run corn out the back of the rotor, closing the concave will help this situation, also waiting for forage to dry some...removing every other wire helps prevent rotor loss too but you probably already tried that. We have all wires in our 1688, but we like to shell corn in the morning and cut beans after 11 AM, back to corn before dark, so we rather skip the concave cover plates if possible = we don't raise as much beans as we do corn...best deal is pull every other wire and run three concave cover plates in the front for beans and wheat [small grains], remove the plates for corn.