1This typical setup is a Yanmar 3GM engine with the raw-water pump driven
by a belt from the end of the crankshaft.
All engines vary to some extent, and some
pumps are driven by gears or pinion shafts;
these are bolted directly to the engine.
Depending on the engine/pump configuration, it can often be easier to remove the
pump from the engine to change the impeller. One important caveat here is to shut
off the water at the seacock. Undo the pipe
clamps, and after removing the securing
nuts and bolts, pull the pump clear.
2With the pump on the bench or saloon table, undo the bolts or screws that hold
the cover plate in place. These are often
small, so it’s a good idea to store them temporarily in a cup or can, as they can easily
roll into the bilge, never to be seen again.
3With all the bolts removed, lift off the cover plate. If it’s stuck in place, insert
the blade of a sharp knife into the joint to
pop it free, or try gently tapping the edge of
the plate with a small rubber mallet or the
wooden end of a screwdriver. These tricks
help you avoid cutting the O-ring seal that
may be used on some pumps.
4I like to use a set of channel lock pliers for removing the old impeller. Grasp the
central portion of the impeller and pull it free.
You might have to wiggle it a bit to release it
from the spindle. Many DIYers prefer a dedicated impeller-pulling tool that fits the pump.
5If you don’t have a pair of channel lock pliers at hand, or the impeller is well
and truly stuck, use a couple of flat-bladed
screwdrivers. Use them at 180 degrees to
each other, in the manner shown, to lever
out the impeller. Take care not to mar the
edges of the pump.
6With the impeller out of the way, now is a good time to inspect the pump
housing. Give it a good wipe out with a
clean rag, then check for deep scoring or
other damage. Small scratches and dings
are unimportant, but if the body is badly
corroded or worn, consider replacing the
pump. Most pumps have a raised interior
portion to flex the impeller blades. This can
be replaced in some pumps; do this if it’s
worn or the edges are sharp.
7A paper gasket will probably remain stuck either to the pump body or to the
cover plate when it’s removed. Use a razor
blade or sharp knife to clean it off; don’t be
tempted to reuse the old gasket, as it will
almost certainly leak, and unless the cover-plate seal is airtight, the pump won’t work
correctly. In the absence of anything else, I’ve
cut a new gasket from an old chart. Instead
of the paper gasket, some cover plates have
an O-ring, which should be renewed.
8With everything cleaned up, we’re now simply working in reverse order.
Smear a little glycerin onto the inside of
the pump body.
DO IT YOURSELF
nance issue, and I then can relax knowing
that when the boat goes back into the
water, the water pump is in tiptop condition. Often water pumps are ignored for
too long and are apt to fail at the most
See the February 2017 issue to learn
how to service an outboard water pump.