The wear plates should be all the way back on all locations! There should not be any wear plates near the knife head area. The knife has to move fore and aft as it strokes.
The pin should not be loose in the arm. The bolt should be torqued to I believe 150 ft-lbs to retain the pin for the knife head. If it wiggles, it can break the knife head or arm. Tight, tight, tight!.