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The water pump impellor
I am now of the opinion that
this is a job to be done every two years but that is nothing to do with the impellor.
With normal Drascombe leisure use that should last much longer. What needs
regular attention are the drive shaft splines which are mentioned below. I
would not expect a dealer to necessarily inspect the impellor in every annual
service unless the tell tale flow was low although he should do so if he is
charging you for a full 100 hour service. The distributor follows the company
line and says inspect the impellor at 100 hours. My dealer suggests inspecting
it every two years. In years past when I had a strong cooling water flow I used
to inspect impellors only at five years (250 hours for me). I would always find
them in good shape, probably good for as long again,
but I would replace them anyway so that I didn’t have to worry about the issue
for another five years. If you do high hours in a silty water environment you
may want to inspect yours more often. However, there is an issue with these
engines that if the drive shaft splines are not greased, then if you leave it
too long, they can seize in the crankshaft, making dismantling to get at the
impellor a serious problem. In fact in more recent operation manuals for these
engines, lubricating the driveshaft splines now appears as an item on the
annual maintenance list. Accordingly I now remove the lower unit every two
years to grease the drive shaft top splines. Having gone to the trouble of
taking the lower unit off it then makes sense to look at the impellor anyway.
Replacing the water pump impellor
If disassembly
works as it should this is not a difficult job
requiring any special skills or tools. It is just that re-assembling the gear
linkage can be fiddly. However it will succumb given patience. I have had a lot
of practice and it generally takes me about half an hour to do the whole job and
that is with the extra care and attention to detail that an owner not being
paid by the hour can give.
The first part
of the job is to separate the gear case from the base of the leg of the
outboard. The gear case is a little easier to handle if the propeller is off
but removing it is not essential. It is not necessary to drain the gear oil for
this operation. However, for safety you should in any case remove the spark
plug lead.
The rod
passing down inside the leg and which actuates the gears is in two parts which
need to be separated. Shift the gears into reverse and look for the big rubber
bung on the starboard side of the leg a few inches above the anti aeration
plate. Take the bung out and you will see the clamp which holds the two parts
of the rod together (see picture). Slacken, but do not remove, this clamp so
that the lower rod will slide out when the gear case is removed.
Now remove the
two bolts under the anti-aeration plate which hold the gear case on. The one at
the rear needs a 13mm spanner or socket. The other at the extreme front
requires a 10mm spanner or socket. Guide the gear case away from the leg. If it
does not come easily place a block of wood on top of the anti-aeration plate
and tap the wood gently with a
hammer. The plate is a light alloy casting and it will crack if you hit it too
hard. Tap first on one side then on the other. If it still does not want to
separate then stop. Don’t force it. However, in most cases, once separated, the
gear case will come away relatively easily. There is no gasket. On all but
early engines, to drain the leg, there are holes at the front near the join.
While you are here make sure that they are not obstructed.
If you are one of the
rare unlucky ones and your gear case did not come away as it should then read
this. Unless you have
a well equipped mechanical workshop I suggest that at
this point you put the bolts back, re-tighten the gear rod clamp, replace the
bung and take the motor to a main dealer. There are several possibilities for
the gear case not coming away. It may, for example, just be stuck. However, the
worst case is as follows. There are two rods in the leg. One is the two part gear actuating rod visible through the hole when
the big rubber bung is removed. The other is the drive shaft. At its lower end
the driveshaft passes through the water pump impellor, which it drives by a
keyway, and below that it has splines which drive the gears. At the top of the
drive shaft are splines which engage in the crankshaft. When you separate the
gear case from the leg, the splines at the top of the drive shaft should
disengage from the crankshaft so that the drive shaft comes away with the gear
case. You can then proceed as below. However, if corrosion has caused the drive
shaft splines to seize in the crankshaft, then upon separation, if you force
the gear case away from the leg, the drive pin key which engages in the water
pump impellor will be forced through the water pump bearing. The drive shaft
will remain stuck in the crankshaft and the gear case will come away with only
the gear rod protruding. The engine will have to be separated from the leg and
special tools then used to get the seized drive shaft out of the crankshaft to
make re-assembly possible. So – if it doesn’t come easily – don’t force it! The
cause of all this pain will likely have been a combination of modern close
tolerances, inadequate corrosion protection being applied to the splines on the
assembly line and a long period since any grease was applied afterwards. This is
why I grease the splines every couple of years even if I don’t need to change
the water pump impellor.
Assuming the
gear case came away as it should, and as it will in most cases, then you will have a gear case with a gear rod and a drive
shaft sticking out of it. The water pump housing is on top of the gear case
with the drive shaft going through it.
Undo the four
bolts holding the water pump housing down and lift the housing up watching out
for the little pin that rests in a cut out in the drive shaft and which acts a
key to drive the impellor. This may drop out as you separate the water pump
housing. In the picture below it is held in place with grease prior to
reassembly. The pump housing may need helping up by gently easing a knife into
the joint but try not to damage the gasket or mating surfaces.
As the housing
comes up, the proboscis that is the water pickup tube should come too.
Take the
housing right off the top of the drive shaft, remove the impellor and inspect it.
If cracks in the rubber indicate perishing, if it shows signs wear beyond the
polishing of the lobes which is to be expected, or if it is more than a few
years old -
then replace it. If the water pump gasket(s) is damaged in
the process then that will need to be replaced also. The gasket is a three part one with a metal centre leaf. The shiny surface
inside the pump housing on which the impellor bears is an insert with a low friction surface.
If it is undamaged the insert does not need to be removed.
This is a five year old 250 hour impeller. You might not be able to
see it on your screen but tiny cracks in the middle of the rightmost lobe of
this impeller indicate that deterioration is just beginning.
To
re-assemble, first clean up the faces where the gasket bears, replace the water
pump gasket(s) if it was removed, put the pump end of the water pickup tube
into the pump, put a little grease on the flat in the drive shaft to hold the
drive pin in place, then lower the impellor down the shaft aligning the keyway
with the drive pin. Wipe a thin smear
of grease around the inside of the pump housing where the impellor bears then
lower the pump housing down the drive shaft. Rotate the drive shaft clockwise
whilst pushing the housing down over the impellor and locating the gear case
end of the water pick up tube (the proboscis). It is important to rotate the
shaft clockwise otherwise the impellor lobes will be pointing the wrong way.
Replace the
four bolts with their washers and nip them up firmly but remember you are screwing
into light alloy. For the record the torque setting is 8 Nm or 70 lb-in (not
lb-ft!). One end of the water pick up tube should be in a bush/seal in the
front of the pump housing and the other in the bush/seal directly above the
pick up screen which itself is under the anti-aeration plate. There is another
bush/seal on the top of the housing. When we put the bottom unit back this will
fit over the tube that is in the leg to take the water to the power head.
It is essential to grease the splines at the
top of the drive shaft with 2-4-C or other water resistant grease so that the
shaft will still come out easily again next time! Clean the splines carefully
and ensure that the grooves are all filled with grease since if you just liberally
apply grease on the surface, most of it will be wiped off as you insert the
shaft up the leg. The splines in the picture below are on a drive shaft in a
lower unit that has just been removed.
There are
shiny bands on the drive shaft and the gear rod a few inches above the pump
housing caused by support bearings at the lower end of the leg. I generally clear
any salt deposits and wipe a little grease on these shiny bits.
Now is the
moment when your patience may be tested. Murphy’s law
says that if you are patient and allow lots of time it will all go together in
a moment. If time is short you may be cursing for hours. You are going to align
at the same time :
1. The
driveshaft splines into the crankshaft.
2. The
bush/seal on the outlet tube on the top of the pump housing with the water tube
hidden in the leg and which carries the water up the leg to the power head.
3. The lower
part of the gear shift actuating rod through the clamp
holding the two parts of the rod together and the top end of the extension
of this rod with the grommetted hole which it goes
through at the top of the leg before it can actuate the reverse lock hook.
My experience
is that the crankshaft splines are not a problem. There is a long guide tube
which you cannot see but which assists this exercise. You may need to just move
the flywheel a tad to line the splines up. The water outlet tube is also not a
problem provided the gear case is reasonably well lined up with the leg. By lining
these items up with the respective mating hole and tube and gently bringing the
lower unit and the leg together these two items usually give no resistance.
The fiddly
part is the gear shift actuating rod. The aim is to get the two parts of the
gear rod held loosely in the clamp and the lower unit within an inch or so of
being back into place. Then focus on getting its top end to exit the grommetted hole (see picture) at the top front of the leg.
Before we
start, in order to ensure that the two parts of the gear
shift actuating rod align properly with each other, we need the shift
lever on the engine and the rod going into the gear case both to still be in
“reverse”. Check that the lever on the engine is still in reverse and push
downwards on the rod sticking out of the gearcase.
Pick up the
lower unit and insert the drive shaft into the leg and through the support hole
in the leg.
Now look
through the big hole in the side of the leg. Hopefully the clamp will be
hanging limp from the upper part of the rod. If so you can use a piece of wire
or string through the big hole to support the clamp so that you can get the
lower part of the rod to pass through its grooves in the clamp. If you undid
the clamp too much so that it is in pieces, you first need to reassemble it. If
the clamp separates and the parts drop inside the leg, don’t panic, just move
the gear case away again and with the leg vertical the parts will fall out so
you can have another go.
When the two
parts of the rod are held loosely by the clamp, line up the water tube and
bring the lower unit and the leg closer together. You will usually find that
the process stops with an inch to go. Don’t force it.
You now need
to guide the top of the rod into its hole at the top front of the leg. It helps
to understand that the grommet protrudes downwards a few millimetres below the
hole. I have found that if you actually remove the grommet you can see what is
going on and get the rod into the hole quicker. The downside is that with the
rod through the middle of it, the grommet is more difficult to get back than it
was to get out. A little washing up liquid and some careful persuasion with a
blunt screwdriver may help, otherwise you will have to withdraw the lower unit
a little, put the grommet back and get the rod through the grommet the hard
way.
When
everything is lined up and engaged, do up the two bolts that secure the gear
housing onto the leg. The torque setting is 70lb in or 8Nm again. Then tighten
the clamp, put the bung back and if you had the prop off, grease its splines
and put it back. The thrust washer should have remained in place so replace the
Propeller, washer, castellated nut and split pin. Do
not overtighten the nut. Just nip it up firmly then
back off as necessary to get the hole for the split pin to line up with a gap
in the nut.
Ideally use a
new stainless steel split pin. If you have to re-use the old one bend both legs in such a way that if one leg breaks off the
other will still stop the nut rotating. Never use a pin with a broken or even
cracked leg and do not bend the legs too sharply as a sharp corner will
encourage a fracture. Replace with a new one as soon as you can. Do not use an
ordinary steel one because, as a friend discovered, once it has rusted the nut
will undo and the prop will then drop off as soon as you select reverse.
If you are
concerned that you may have disturbed the gear positions, then with the plug
lead still off, you can check the gear shift
operation. First temporarily disable the “start in gear lock” at the flywheel, (help up by a piece of wood in the picture) then
pull the starter cord. You should still have reverse gear selected so ensure
that the propeller rotates backwards (to determine what is backwards, imagine
it screwing into butter). Then successively select neutral and forward gears
watching that the propeller does not rotate in neutral but does rotate forwards
with the gear lever in forward. If the gear lever does not line up,
particularly in neutral, then off with the bung and adjust the clamp.
Now you can
replace the spark plug and if you have done the rest of the service you are
ready for another year.
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