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BOATWORK<br />
Release snap ring<br />
to remove impeller shaft,<br />
bearings ands seal<br />
from housing.<br />
Old impeller shaft (below) is worn. New shaft<br />
above.<br />
boat. Like a radiator, engine-cooling water circulates<br />
through the engine, and heat is shed as air passes through<br />
the radiator, effectively cooling the water. Your heat<br />
exchanger works in principle the same way, but uses seawater<br />
instead of air to cool the engine water. So what you<br />
essentially have is a radiator that is encapsulated in a water<br />
jacket where raw seawater is pumped through the water<br />
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jacket, effectively cooling the engine water, and then exiting<br />
the boat through the exhaust system. The cooled engine<br />
water continues its route in the closed system going to the<br />
cylinder heads and block via a gear-driven pump and then<br />
back to the heat exchanger to begin the route again. Your<br />
engine actually has two water pumps. The freshwater pump<br />
is gear-driven off your accessory gearbox, and your raw<br />
water pump is mounted on the front of the engine and operated<br />
via a pulley/belt system.<br />
The raw water pump is a simple design, and anyone<br />
can rebuild one with some basic tools. The weak link in the<br />
pump itself is the impeller. Search the archives and you will<br />
find my article on impeller replacement. While an impeller<br />
change is recommended every year at the beginning of the<br />
season, a pump rebuild involves more than just an impeller<br />
and gasket change, and you should get many, many years<br />
out of your pump before the next rebuild. The rebuild<br />
involves removing the impeller shaft, bearings and gasket.<br />
You will need to remove the pump from the engine to perform<br />
this repair. Disassembly is pretty straightforward.<br />
Remove the screws on the impeller plate, pull out the<br />
impeller, shaft keyway and cam plate. Turn the pump over<br />
and remove the c-clip. Hold on to this clip, as it can be reused.<br />
The bearings and impeller shaft will come out as one<br />
piece. You may need to press them out and coax them with<br />
some grease and penetrating fluid. A good sign is when they<br />
come out easily. A bad sign is when they are hard to get out,<br />
which means seawater has seeped past the seal, and some<br />
galvanic corrosion has taken place. Once the impeller shaft<br />
is free from the housing, inspect the shaft for wear, nicks and<br />
grooving. These are signs that the bearings have failed and<br />
allowed the shaft to wobble in the housing. As you can see<br />
in the photos, the original shaft is damaged, and both shaft<br />
and bearings require replacement. Take the old one, clean it<br />
up and stick it in your desk at work for a conversation piece.<br />
To install your new shaft and bearings, you must first<br />
mount the bearings onto the shaft in the proper location.<br />
Note there is a machined groove on the new impeller shaft.<br />
That is a marker to tell you how far to press the bearings<br />
52 September 2010 SOUTHWINDS www.southwindsmagazine.com
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