Simplicity1694744 18hp

What is the bushing on the hydro Grear pump part 31serve does the pulley fit flush on the pump shaft.

I know not what you are talking about. Part 31 is not a bushing it is a Simplicity 5023420 Valve Plate. Pulley fitting flush with what? Flush with the end of the shaft or flush to pump? I have always put pullies on till they will not move any further then tighten up whatever mounts it to the shaft.