Need to set up the knives on my 718. Housing is moved up as far as it will go, shear bar is near the end of it's adjustment, and it doesn't blow corn silage very well. Knives are in the middle of their adjustment slot. Problem is the bolts that hold the knives are worn enough that the socket won't hold to turn them. Got a couple loose with a 3/4" breaker bar with an 18" cheater pipe on it, but most are rounded enough that socket just slips up and off. tried heating the knife holder behind the knife where the bolt screws in, but the knife started to turn red and I would think they are heat treated, so that's not good. Anybody got any suggestions on what to do next? Chopper really in pretty good shape, so hate to walk away from it, but may have to.