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Though it's not a hard job there always seem to be questions on rebuilding the water pump or replacing the seals on these machines. There are several seals that need replaced and some of them need to be installed in a certain direction so I suppose that is where some of the confusion stems from. One thing I want to mention before we get started is the pump shaft and bearing. If you have never replaced it I recommend that you do so. The water pump is driven directly off of the crankshaft. There is a slot cut into the end of the crank that the water pump shaft fits into. If the water pump bearing locks up it will twist the end right off of the crankshaft and then you are screwed.

There are 4 different seals that you will need, one on the bolt that holds the impeller on, the ceramic seal that fits under the impeller, the mechanical seal and an oil seal that are driven into the clutch cover. The mechanical seal and ceramic seal come as a set, here are the part numbers:
Pump shaft: 17510-01C00
Mechanical and ceramic seals: 17470-02F00
Oil seal: 09282-10013
Impeller bolt seal: 09168-06025

To get started remove the clutch cover and pull the water pump cover. The water pump cover seals to the clutch cover with an O-ring that shouldn't need replaced however you may want to pick one up just in case. I didn't list the part number for that because you probably don't need it and it's a different part for the zilla and the 250. Remove the bolt holding the impeller to the shaft. Remember it is a left handed thread. You can use a crescent wrench on the back of the shaft to hold it while you break the bolt loose. The impeller will probably be pretty tight to the shaft so you can use two screwdrivers to pry it up. Do not pry directly off the case, put a thin piece of wood or something between the screwdriver and the case, you don't want to ding it up where the water pump cover seals. If it doesn't want to come straight off try wiggling the screwdrivers back and forth. Once that is off flip it over and you'll see the ceramic seal on the back of the impeller.

Now you want to drive the shaft out. Use a large plastic dead blow and drive it from the outside of the clutch cover toward the inside. You want to protect the sealing surface of the clutch cover while you are wailing away on the shaft, what I did was laid a flat piece of cardboard on my bench, worked fine. Once the shaft is out flip the cover over so you are looking at the inside. Down in the hole where the shaft came out of is an oil seal, use a pick to pull that out. Be careful that you don't gouge the sides of the hole and ruin the sealing surface. With that seal out you need to put an extended socket down that hole and drive out the mechanical seal from the inside of the clutch cover toward the outside. Be careful here, if you look down the hole you will see a lip that the oil seal you just pulled sets on. Be sure you are not beating on that lip when attempting to drive out the mechanical seal. Clean up all the surfaces where the seals go and you are ready to install the new seals. Here are a few pictures of the new seals.

First drive the oil seal back in from the inside then flip the clutch cover over and drive the mechanical seal in. You could probably drive the shaft in before the mechanical seal if you were afraid of messing is up while installing the shaft. Either way use some engine oil to lightly lube the shaft before you install it to help it slip easily into the mechanical seal. Once those things are in you need to put the new ceramic seal into the back of the impeller. Once you have done that lubricate the ceramic and the end of the mechanical seal where it rides with a bit of antifreeze before you reinstall the impeller. I just dip my finger in the old antifreeze and wipe it around. This may not be necessary but it only takes a second and assures there was some lubrication on startup.

Now pay attention to the seal on the bolt that holds the impeller on. There is a ridge on one side of it that goes towards the impeller, you should be able to see it on the old one when you remove it. You can also see part of it in the picture above at around 10 or 11 o'clock. There is a second washer on the bolt behind the seal, just leave it on the bolt and install the new seal on top of it. Once you have torqued the bolt you are ready to reinstall the clutch cover. Before you put it on make sure the rack that sticks out from the center of the pressure plate is turned the correct way so that the teeth will engage with the teeth on the pinion which is pulled by the clutch cable. Also try to line up the water pump shaft with the slot in the crankshaft where it rides. We left the water pump cover off at this point on purpose so that if it isn't perfectly lined up we can turn the water pump one way or the other to let it fall into the slot in the end of the crank.

That's it. Put everything together, fill up the fluids and you're done. I'm sure everyone knows about the small bleeder bolt on top of the head but just in case, take that bolt out when you refill the radiator and it will bleed all the air out of the system. There is also a drain on the bottom of the water pump cover that does a much cleaner job of draining the system than just yanking the hose off, lol.
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