Place the pulley on the pump shaft as best as possible. Be quick as it ill cool fast.
In the center of the pump shaft is a hole that has threads. It might not look like it because of it being dirty, but they are there. Get a bolt and large washer. Place the washer down on the pulley, the bolt through it and start threading the bolt into the pumps shaft. This will help pull the pulley down and onto the pump shaft. Remember it's a VERY TIGHT FIT! Another way is to use a block of wood and place it over the pulley and hammer it down straight. I would recommend using a press though.
505zoom is writing up a how to.