I have made two attempts to disassemble a Goulds Model 3656 4" inlet water pump. Attached to a 15 hp Baldor Motor at 3500 rpm.My problem is separating the adapter from the casing. The casing has two notches 180 degrees from each other and I'm assuming these are there to place a tool (that I don't have) there to pull them apart. I'm using a cold chisel and a hammer. When I do this the adapter flange breaks. I am attaching pictures. I appreciate any help with this issue. Thank you!