Mercury 4hp Impeller Replacement

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AdamH

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I'm about to replace the cooling water impeller on my 2006 Mercury 4hp 4-stroke sailpower outboard - the 'squirt' has stopped! /forums/images/graemlins/frown.gif

Buying one isn't the problem, where is it on the motor? Is it in the 'power head' or somewhere in the leg?

Any chance of a description of where the impeller is or a link to a mercury service diagram?

Many thanks
 
On my Merc. 2.2 it's forward of the propeller, which, obviously, needs to come off, then 2 screws IIRC. BTW, the "squirt" on mine often stops, but it's never the impeller, which is now several years old. It's almost invariably blocked water passages caused by my neglect.
 
First thing to do is check that the pee hole is not blocked, and to check right back to include the connection on the engine.

The pump is down on the gear box. I guess a 4 hp engine has a clutch even if not full FNR gears. If it has a clutch the pump will be on top of the gearbox, driven by the vertical drive shaft.

It will entail separating the gearbox from the leg and access to a workshop manual would be highly desirable. (I might not bother myself but i am one of those people who takes things to bits to find out how they work!)


It is only where there is no clutch that the water pump can be behind the prop and driven by the prop-shaft. It must be driven all the while the engine is running.

I don't suppose there is anything that will help but you could look in the "Download center" on the Brunswick marine website


ALSO

You may be able to find an exploded diagram on the Crowley Marine website
 
It looks as though the gear-case is held by only two bolts, as though the drive shaft will pull out of the crankshaft , as though the water-tube will pull out of the water pump and as though there is a joint in the shift rod that can be accessed via a plug in the side of the leg.

The fun bit is getting all the bits to line up when putting it back together.
 
get yourself a copy of sailing today, april edition 2008. it has 5 pages of photos and instruction on how to do exactly that on a 4hp mariner, which i think is the same as a mercury. if you cant get one, pm me and i will post you mine. people have been very helpful to me on this forum and its time for me to do the same. good luck
 
As VicS says, check elsewhere first 'cos it is highly unlikely that there is anything wrong with the impellor on a 2006 motor.

The impellor itself is driven by a little pin which engages a cut out in the drive shaft. Watch out for it and don't lose it. You should see it when you lift the cover of the water pump.

The drive shaft is supposed to come out with the bottom unit. Sometimes it gets siezed (corroded) at the top end where it engages the crankshaft. This makes the job a serious pig. If the lower unit won't come off after you have undone the two bolts and given it a gentle tapping with a hammer via a softwood block - put the bolts back and take it to the best dealer you can find unless you have a good workshop and masochistic tendancies.
 
And if its anything like my Evinrude it's that little pin that is is all that stops the drive shaft pulling out though the water pump. Result is that if the drive shaft is stuck at the top all your efforts to free it result in that pin smashing the water pump housing (Nearly got the Tee shirt on that one)

Grease the splines on the top of the shaft lightly when reassembling.

Agree in couple of years the pump impeller should not need changing UNLESS it has been run dry, even for a few seconds.
 
Hate to take issue with VicS even if it is only a matter of small degree but the pump on this range of motors seems to be lined with something that has a highly polished surface. I reckon that it would take more than a few seconds to damage the impellor. That is not to say that you should run the motor dry for half a minute or for any time at all at more than low speed. However, if it has been subject to the "OK it starts alright now shut down immediately" scenario, that shouldn't be reason on its own to dive into the lower unit.
 
replacing impeller on Marine 4 stroke 4 hp

Laundryman said:
get yourself a copy of sailing today, april edition 2008. it has 5 pages of photos and instruction on how to do exactly that on a 4hp mariner, which i think is the same as a mercury. if you cant get one, pm me and i will post you mine. people have been very helpful to me on this forum and its time for me to do the same. good luck
Click to expand...

this is what I am trying to do. Replace impeller on my Mariner 4 stroke 4 hp outboard (think it is a 2002) but not very successfully as I cant find instructions anywhere on the internet - any suggestions please would be greatful - thanks a mil Ray:encouragement:
 
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As stated above. The pumps are usually sitting in a self contained casing on top of g/box in the lower leg. Usually you just have to undo the bolts holding the gearbox to the leg and slide it out of leg. There is often a need to disconnect the gear change linkage as well although this is sometimes just a simple spline connection.
Once you have the gearbox and drive shaft assembly out of the leg you will see a square/rectangular-ish casing at the bottom of the drive shaft, often plastic. Remove the bolts and dismantle the pump. If you place the components on the table in the order they came off its easier to remember the assembly order. Take digi photos too at every stage.
The rubber impeller will need to be slid off the shaft. This is often stiff and you should clean the shaft of grime first to make it easier. There is a key between the shaft and impeller which will try its damnedest to jump out, escape and hide forever so make sure you keep an eye on it and put it in a safe place as pump will not work with out it.
Top tip for reassembly is to note the direction of the old impellor blades have formed into and when fitting new impeller tie a cable tie around the blades making sure you fold them in the correct direction. Once you have slid the pump top casing over the top of the blades, snip off the cable tie and it should be easier to get the casing on with the fins in the correct direction.
I would always replace the gaskets too and spend ten minutes with some scotchbrite cleaning all the scale off the pump components to ensure an easier start to the impeller's life.

The hardest part is more often than not trying to re assemble the gear linkage. Mariners are easier than most with a simple double nut arrangement. Small Yamahas are a nightmare with rods needing connected through a hole that infant fingers would struggle to access!
 
just done this on the 3.3 Mercury.That little pin really is little, and its not half moon shaped in my case anyway, its like a little needle roller,almost lost/did'nt notice it coming out!
 
Laundryman said:
get yourself a copy of sailing today, april edition 2008. it has 5 pages of photos and instruction on how to do exactly that on a 4hp mariner, which i think is the same as a mercury. if you cant get one, pm me and i will post you mine. people have been very helpful to me on this forum and its time for me to do the same. good luck
Click to expand...
Yes. It applies to the Mariner/Mercury/Nissan/Tohatsu motors of 4/5/6hp flavours.
If the OP is the sort of person who gets frustrated when things don't go right and throws spanners about (like my BROTHER-IN-LAW) he should get it done by a dealer.

I'm pretty certain (it's been a while) that there is a clamp bolt on the gearchange rod behind that big rubber grommet. The recessedbolt just visible above the prop is one of the bolts fixing the gearbox to the leg.

waterinlet.jpg
 
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Laundryman said:
get yourself a copy of sailing today, april edition 2008. it has 5 pages of photos and instruction on how to do exactly that on a 4hp mariner, which i think is the same as a mercury. if you cant get one, pm me and i will post you mine. people have been very helpful to me on this forum and its time for me to do the same. good luck
Click to expand...
 
Hello Laudryman,
I find myself also struggling with reinstalling the lower unit of a Mercury 4 hp 4-stroke. Replacing the impeller went smoothly but getting the lower assembly reattached is proving to be a real challenge. You mentioned the Sailing Today, April edition, 2008 and had offered to help another member with that information. If you still have a scan of that article, I would most appreciate seeing it. There is a trick but I am not getting it. Thank you very much if you can help.
 
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