Dale, When talking about removing back two rows of chaffer to let silks and small corn leaves blow out,you would be looking at the rear most louvers of top chaffer just in front of adjustable lever. This allows air to push debris that collects near rear under top chaffer.As for the snapping roll blade wear if you have more than 1" of radius at leading edge of blade you are going to lose the aggressiveness of rolls to be able to pull stalk down. With this wear you will find that the stalk will be pushed forward before being pulled down and this will sometimes lead to having an ear being thrown forward. Best thing you can do is to have new snapping roll blades chromed and that should be the last set you put on your cornhead. Price for chromed blades is approx. $30_blade. Hyper Harvest II