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Old 18 October 2009, 09:57   #1
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Checking impellor ?

Hi all,
would any of you boffins out there be able to instruct me on how to check/change the impellor in a Mercury Blueband 20hp ?
I have run the engine immersed in water, and also with bellows, but all I get is Steam/exhaust smoke through the blow hole.
Is this a sign of impending disaster, or can it be rectified ?
Regards,
Andy
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Old 18 October 2009, 10:05   #2
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Drop the lower leg off (3 visible bolts, one under the trim tab).

Impeller is on the drive shaft inside a plastic casing. DON'T lose the locator key when you remove the impeller!
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Old 18 October 2009, 15:11   #3
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Could just be a blockage in the hole - pass a piece of fine wire or strimmer line down it first!!!
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Old 18 October 2009, 15:20   #4
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It is almost certainly a sign of no effective water pump operation if steam is coming out.

It is a straightforward task to drop the lower unit and replace the impellor, don't just check it. The widely accepted best practice is to check every year and if OK replace bi annually but if in any doubt replace. An impellor from key parts in watford is about 12 for a sierra bit although a OEM one would be a little more. If you don't have a manual look at the iboats.com website to find out how to do it.

One of the most important reasons to drop the LU off is to grease it up and not let it seize on.

Really its a great little job and will give you confidence to tackle other things on the OB later.
Davej
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Old 20 October 2009, 12:26   #5
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Thankyou Dave, I will look up iboats directly.
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Old 22 October 2009, 14:14   #6
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impellor changing.

Hi, I looked on the iboats site, but could not find the information on how tocchange the impellor on my Mercury 20 HP blueband (200 model).

I was wondering if anyone, maybe Nos , could help by posting the information I need.
Ica't identify the three bolts which have to be removed, and wouldn't know what to do when I removed them.
Apologies for being thick, but was always told by my father " If you need to know anything, ASK"
regards to all,
Andy
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Old 22 October 2009, 17:32   #7
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When you're telling him, please can you also note the bits which would be the same on mine ?? Thanks ever so much ! :-)
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Old 22 October 2009, 20:24   #8
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on the lower half by the prop should be a couple bolts also where your trim tab is usely hides a bolt there look for a rubber stoper and in the hole should be a bolt undo the 3 or 5 bolts then wiggle the botton lose slide it out and look at the bottom of the shaft there is a houseing held on normaly with 4 bolts undo them impelor is inside ,if removeing to replace be sure not to loose the little lockator key inside ,its a little peice that fits in a small slit on the bottom of the shaft has to be realined when you fit the new impelor then bolt it all back together if dun corectly running up there should be a realy good srtong jet of water
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Old 22 October 2009, 21:03   #9
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The pic is of an Opti lower unit. You may have a different number of bolts/nuts, but the principle is the same for all Mercs.

First make sure you know which direction your engine turns in when running. Mark it on the flywheel if it's not marked.

Put the engine into neutral.

Remove the trim tab (Green line-bolt accessable from above-may be an allen bolt). Undo any bolts underneath it when it drops off.

Tilt the engine fully if it's on your transom.

From underneath, undo all visible nuts (red lines-don't use a socket )-remembering to leave one of the forward nuts on a couple of turns. This stops the lower unit falling off suddenly.

Give the lower unit a pull downwards in line with the leg. It should come loose and drop against the last nut. If it doesn't, wiggle the lower unit about by hand-hard(ish) while applying steady downwards pressure. DON'T HIT IT ON THE ANTI-VENTILATION PLATE.All this will achieve is a broken anti-ventilation plate. If it won't come off,do it all back up and take it to a techie. All you'll do is break it if it's stuck.

Once it's dropped against the last nut, undo that last couple of turns and the lower unit will drop.Don't let it impale you or hit the floor.

On the separated lower unit, undo the impeller housing bolts (purple line-may be more or less than the 4 visible). Lift the housing off. It'll be stiff to move so do it carefully as you don't want to damage the gasket face underneath. This will expose the impeller. It'll probably look like the one on the right-the one on the left is a new one.


Clean up the driveshaft if it's rusty. (red-yours probably will be, and I'd bet you'll need to cut the impeller off with a dremel-carefully and on the opposite side to the keyway)
If it'll come off, lift the impeller off (DON'T LOSE THE LOCATING KEY!).

Clean off the old impeller housing gasket. Put a new one on with a thin smear of grease on it.

Put the new impeller on. To get the housing to fit down onto it, grease the inside with a very thin smear of grease and push it downwards while turning the driveshaft in the direction the engine turns. Grease all the splines on the driveshaft and gear selector shaft lightly. Too much will make it hard to refit the lower unit.

Refit your lower unit,making sure it's still in neutral and the gear selector rod and the water pickup pipe are correctly located.If it's dropped into gear, put it back into neutral using pliers with a rag inside the jaws. The driveshaft probably won't line up immediately. To line it up, turn the flywheel slowly.

Do all the bolts up and test it...
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Old 23 October 2009, 12:03   #10
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impellor

Thanks for that, I will attempt to dismantle it tomorrow and will post(maybe with pictures) if I get into difficulty. I have to go to the boat shop in the morning to pick up control cables, so I will get a new impeller then.
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Old 24 October 2009, 12:28   #11
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impeller

Latest update :

Went to Bristol Boats this morning and bought a new impellor.

The diagram above is not the same as my engine, so I asked the engineer at the boat shop. I was told to remove 3 bolts, 2 from under the cavitation plate, and one on the transom side of the engine, above the cavitation plate.

This I have done, but still cannot remove the bottom end. I took someones advice and used a block of wood and a hammer on the prop housing, but still it will not move.
I inserted a screwdriver in the gap as a wedge, but only succeeded in breaking off a small part of the casing.

Any other sugestions please ?
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Old 24 October 2009, 16:52   #12
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Quote:
Originally Posted by redxpuser View Post
Latest update :

Went to Bristol Boats this morning and bought a new impellor.

The diagram above is not the same as my engine, so I asked the engineer at the boat shop. I was told to remove 3 bolts, 2 from under the cavitation plate, and one on the transom side of the engine, above the cavitation plate.

This I have done, but still cannot remove the bottom end. I took someones advice and used a block of wood and a hammer on the prop housing, but still it will not move.
I inserted a screwdriver in the gap as a wedge, but only succeeded in breaking off a small part of the casing.

Any other sugestions please ?

Pay an engineer or buy another engine mate.

No insult intended here-if you couldn't figure out which bolts/nuts to undo from that last post of mine you don't have the necessary skills to work on an engine that you'll be relying on to get you back to shore.
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Old 25 October 2009, 03:03   #13
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impellor

Well thanks a lot,
your last post would have been really helpful IF it was anything like the engine I have. As it was Nothing like my set up, I didn't find it very useful. You say I haven't the skills needed, that's why I was asking for help in the first place.
As you are only in Swindon, maybe you could recommend an engineer who could take a look at it ?
Otherwise, one scrap engine !
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Old 25 October 2009, 04:35   #14
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Who are Bristol Boats ? D'you mean Force 4, or am I missing out on potential shopping opportunities ??

Anyway, back to the point, if they are unable to help you could try Samspeed who are near-ish (on the A38 towards Gloucester). I've heard both good and bad things about them, and they have a tendency to be expensive, but could be worth a go. I'll send you a PM with their number as I don't know if I'm allowed to post it.

(BTW, I haven't tried taking my engine apart yet but can see myself ending up in a similar situation before long, so hope you get it sorted without too much expense!)
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Old 25 October 2009, 04:44   #15
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Look, it really wasn't an insult. Note what I said at the beginning of the post:-
Quote:
Originally Posted by me
The pic is of an Opti lower unit. You may have a different number of bolts/nuts, but the principle is the same for all Mercs.
From what you've said you simply don't have the general mechanical knowledge to be working on something you're going to be relying on to get you back to a place of safety. It simply needs building up on something less critical to your survival.
There's no shame in it-if I tried to do your job I'd just make an expensive pile of firewood.


Anyway, back to the point.


If you want a recommendation or a good engineer,it's a bit of a trek but try Mike at Redline Outboards in Abingdon. If he can't remove it, no-one can.
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Old 25 October 2009, 04:53   #16
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Quote:
Originally Posted by Shaz View Post
Who are Bristol Boats ? D'you mean Force 4, or am I missing out on potential shopping opportunities ??

Anyway, back to the point, if they are unable to help you could try Samspeed who are near-ish (on the A38 towards Gloucester). I've heard both good and bad things about them, and they have a tendency to be expensive, but could be worth a go. I'll send you a PM with their number as I don't know if I'm allowed to post it.

(BTW, I haven't tried taking my engine apart yet but can see myself ending up in a similar situation before long, so hope you get it sorted without too much expense!)
They are actually the guys I was telling you that'd have spares for your engine but I couldn't remember their name Google them.

You're less likely to have the lower unit stick-your engine is 15 years newer.
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Old 25 October 2009, 10:05   #17
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Quote:
Originally Posted by Nos4r2 View Post
They are actually the guys I was telling you that'd have spares for your engine but I couldn't remember their name Google them.

You're less likely to have the lower unit stick-your engine is 15 years newer.
Ah brilliant - will have a look.

Nope, mine didn't stick, had forgotten it's American so normal metric sized tools no use, and every bolt appeared to be a different size, but other that I think it's done. Thank you for instructions, very useful ! I was hoping for live online support, but unfortunately our wireless doesn't reach over the road so I had to rely on the diagram. It's not the same, but similar enough to make sense. :-)

However, I can't test it cos I've got a broken bit of pipe which looks like it may be important - hopefully it will show up in the photo - the end appears to have sort of corroded and broken off something but I can't see anything obvious that it was attached to. Does it go inside a metal pipe or is there another plastic/rubber bit that it should clip to ?
Also is there a name for it so I can Google for instructions on what to do with it ?
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Old 25 October 2009, 13:04   #18
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Is it copper or plastic? I think I can see 2 bits of pipe in the pic. Hopefully it's not your water pickup tube.
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Old 25 October 2009, 14:38   #19
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It's plastic. I thought it probably was something to do with water pickup but it looks really small for that - it's only about 1mm internal diameter.

I spoke too soon about everything else being a success, I can't get the lower unit back on ! After much wiggling it will go as far as allowing the bolts to just about locate, but it won't lift any further and I don't want to try doing them up tight as it wasn't that much of a struggle taking it off, and I don't want to break whatever is in the way.

It's going to have to wait til next weekend now so plenty of time to identify random plastic bits and what to do with them.
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Old 25 October 2009, 17:29   #20
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Has the water pickup tube located in the pump housing?
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