Impeller won't suck!

[forelle541]

I had this a year or two ago, air was sucking in past the shaft seal, once the pump primed the water pressure pushed the seal against the shaft so no water leak, turned out to be a broken seal spring, I now change the seal coil springs for o rings.

 

[stu9000]

Is suspect predictive text strikes again and you have a sail drive which when the boat is inverted becomes a sky drive
The water passage through the leg is notorious for blocking muck and shellfish you need to rod it through from the hole at the bottom at the nose the side grill is in addition.
You also need to take the new front cover plate off and remove all the goo just use the correct gasket with a little light grease.
You do possibly have a backing or wear plate behind the impeller which does wear badly and needs checking
It is possible that you have disturbed the shaft seals when changing the impeller this would cause a lack of suction
Probably best to take the pumpthe of and check it out

thanks.
Not sucking from a bucket so I don't think it is a blocked inlet.
I will use less sealant next try.
The front plate was pretty worn and there was a spare just as bad in the bits box.
So maybe the rear is heavily worn.

Ta

 

[stu9000]

Answers to your points below...

If the plate was worn then perhaps the body is worn.

...could well be....

How old is the pump (in hours)
....who knows, I'm guessing its pretty old...

and is there sediment in the water.
...no...

How pronounced is the heal in the pump body which causes the pump action.
...I'm not sure what you mean here...

Did you thoroughly lubricate the new impeller with wash up liquid or glycerin before first use ?
...yes...
Have you got the vanes the right way ?
...yes...

thanks

 

[stu9000]

Or even the forum rules? The word with the asterisks is prohibited, even in asterisked form.

The word needs to be edit out asap otherwise that first post might become the last. :ambivalence:

Richard

gosh!! Missed it. I wonder what he said

 

[stu9000]

I've had similar problems with raw water pump priming.

Here's what I did to solve them.

First, remove the impeller and lightly smear waterproof grease around both ends as well as around the blades before refitting. This overcomes any minor gaps in the pump housing that have been mentioned above.

Second, close the seacock and remove the inlet hose which goes from your water strainer to the inlet of the raw water pump.
Get a bucket of water and a measuring jug or some other jug which holds about a litre and can pour accurately. Holding the hose up as high as it will go (hopefully above the height of the water pump) fill the hose with water using the jug. Hold it there and top up the jug.

With the help of an assistant, start the engine at idle speed only, and as the water disappears down the hose keep topping it up using the measuring jug. Keep doing this until the bucket is empty, then stop the engine. Do not get any air locks in the hose.

Refit the hose to the strainer, trying to keep as much water in there as you can and open the seacock. Start the engine and you should find all is well. System will be properly primed and will continue to pump OK now.

Raw water pumps are fine once they are primed, they just aren't very good at pushing water through an empty system. At least, that's been my experience.

nice tip.
Trouble is , the hose seams to unseal at the pump inlet wen I wiggle it about a lot.
It isn't the jubilee clip. Its the metal fitting that pushes into the pump housing.
I suspect this seal is a big part of the problem.
I will try ptfe tape to try for a good air seal.
A variation of your suggestion would be to tape some hose to the end and feed water from a bucket higher than the pump.

 

[stu9000]

I had the same issue last year with pump not sucking and eventually bought a new water pump. That did the trick. The pump housing was worn.

I suspect the same.
If I can disprove an upstream blockage by getting it to prime ill have to shell out.

 

[Tranona]

Have you actually checked there is water coming up the saildrive. Take the hose off the seacock on the saildrive then open the seacock. You should get a jet of water. If so you know it will get to the inlet to the pump so the air is getting in before the pump, or the pump is too worn to prime.

 

[jiris]

As this is your first post welcome to the forum.

I wonder if you had read the forum title?

Guilty as charged. Sorry...

 

[vas]

if every other suggestion has failed, maybe you should check that the axle is not worn, remove the impeller (and the belt!) see if you can wiggle the shaft (or easier the pulley), if you can bearing and seal at the back of the assembly has gone. On my yanmar 2gm20 the price of a new pump was astronomical, so got my machinist to do a full rebuilt, turned a new axle on the lathe and fitted it all back together. Was 20yo and 1000h old. Works fine now!

V.

 

[Daydream believer]

. On my yanmar 2gm20 the price of a new pump was astronomical, so got my machinist to do a full rebuilt, turned a new axle on the lathe and fitted it all back together. Was 20yo and 1000h old. Works fine now!
V.

And if the truth was known it probably cost as much, but like a lot of things the cost was " hidden" which always makes one feel better if nothing else :encouragement:

 

[vas]

And if the truth was known it probably cost as much, but like a lot of things the cost was " hidden" which always makes one feel better if nothing else :encouragement:

not in the UK, whole thing cost me 50euro iirc, here in Greece.
Now, get a new pump for 50euro/usd/quid and then we are talking

V.

 

[Dipper]

Post deleted. Someone else already said it!

 

[VicS]

I may be wrong but I have a feeling that the impeller needs to have close contact with the cover otherwise water can flow around the outside edges of the impeller making it ineffective. If there is a thick layer of sealant then this would not allow a tight fit.

Absolutely. The cover should be fitted with the correct thickness gasket. If its too thick then the impeller wont seal against it ( or the back of the pump body) If its too thin then the impeller will be too tight a fit and may become damaged.

 

[stu9000]

Thank you lads.
A few strategies to try.
Much appreciated
S