I need to replace the water pump on my 1984 BMW 733i E23. I drained and removed the radiator (one screw on the driver side, one screw on the passenger side) and then I undid the four 10mm bolt-and-nut combinations that attach the fan to the fan clutch. To my surprise, the fan didn’t come off. It was loose but something was still holding it in. A 13mm bolt in the center of the pulley shaft was the culprit.
When I tried to loosen that bolt, I was unable to keep the pulley in position, to prevent it from slipping. I stuck a screwdriver vertically behind the fasteners that attach the pulley to the water pump, to try to keep the pulley from slipping. I failed, but in the process I broke some of the aluminum teeth off the fan clutch. Dangit.
Fortunately, I also have a 1983 BMW 733i E23. I tried plan B, on that car. I bought a long 10mm bolts and stuck it into one of the holes for the 10mm bolt that connect the fan to the fan clutch. This provided enough leverage so that I could retry my vertical-screwdriver trick again, but this time the screwdriver was pushing against the long 10mm bolt instead of the fragile aluminum teeth. Better. 🙂
Next, I need to undo the four size 5 metric Allen bolts that attach the water pump pulley to the water pump. In preparation, I loosened the alternator-and-water-pump belt by loosening the 13mm nut at the back of the top of the alternator.
The Allen bolts were so tight that the pulley slipped again. The end of the shaft is slotted so I stuck a long steel plate into the slot so as to immobilize the shaft. Even so, I couldn’t budge the Allen bolts. So, I tapped them with a hammer and now they are soaking in penetrating oil. I expect that will make them viable to remove.