Johnson raw water pump just won't prime - new impellers

[Modulation]

Johnson raw water pump just won\'t prime - new impellers

My raw water Yanmar 2gm20 has done about 300 - 400 hours. In the winter I replaced the impeller with a new one which simply didn't pump any water. I thought the waterways must be furred up so I dealt wit that. Still no change however. So the old one went back in - worked fine. I fitted another new one this spring - still won't pump. On close examination of the impellers I noticed that the 2 new ones are very slightly shallower than the old - about 0.2mm. The dia is the same.
I contacted Aquafax the Johnson distributors, who were mystified, and they sent me a 3rd impeller gratis - same result.
All the parts are genuine stamped Johnson. The pump is a little bigger than usual - an F4B - but that shouldnt make a difference. And anyway it's the one that came with the engine.
Any insights, anybody?
The pump is a fully cast job ie the cam is integral.
In desperation I'm thinking of having 0.2mm skimmed off the pump body face.
Oh, and yes , I checked the cover plate too. It had little wear but I replaced it anyway to no effect.

 

[ctelfer38]

Re: Johnson raw water pump just won\'t prime - new impellers

You did'nt mention greasing the impeller and housing on inserting the new one. Done that? /forums/images/graemlins/cool.gif

 

[Poignard]

Re: Johnson raw water pump just won\'t prime - new impellers

Forgive me if this is insulting your intelligence, but is the impellor turning? I have a BUKH engine and failure of the drive to the pump is not uncommon. Also, is the suction line clear and free of airleaks?

 

[FlorealIII]

Re: Johnson raw water pump just won\'t prime - new impellers

Try greasing the impeller with glycerin , do not use mineral oil or grease . Why not priming the pump yourself by filling it with water before starting engine ?

 

[Robin]

Re: Johnson raw water pump just won\'t prime - new impellers

These impellors also seal against the face plate of the pump so air may be leaking past there, especially if you say the new impellors are shallower by 0.2mm. Maybe there is a thinner gasket for the new ones but more likely is that there is some wear on the faceplate and the new ones being thinner don't work. You could try rubbing the faceplate down to remove wear grooves on some fine wet/dry on a very flat surface (piece of glass maybe). Some faceplates can be reversed to use the new inner face, but not if it is engraved.

 

[philip_stevens]

Re: Johnson raw water pump just won\'t prime - new impellers

Go to ASAP-Supplies, click on Pumps and Domestics, then type in F4B in the search box, and see what comes up. There is quite a lot on the F4B.
If necessary, phone ASAP for more info.

 

[Modulation]

Re: Johnson raw water pump just won\'t prime - new impellers

Yes I greased the impeller.

 

[Modulation]

Re: Johnson raw water pump just won\'t prime - new impellers

yes. the impeller is turning. I've tried this both on and off the boat. the key issue is that the old impeller STILL WORKS1

 

[vyv_cox]

Re: Johnson raw water pump just won\'t prime - new impellers

I agree with Robin, very likely there is wear on the front cover plate, or there is a change in the gasket thickness, if it has one. On some of these pumps it is possible to reverse the plate, providing a nice flat surface again. On others it isn't, in which case you could grind it flat if you can be bothered, or buy a new one.

 

[Salty John]

Re: Johnson raw water pump just won\'t prime - new impellers

The 0.2mm seems to be critical - maybe a bad batch of impellers so try buying one from another shop.
The old impeller may have 'grown' through absorption over time and is compensating for the wear on the wear plates.

 

[wanderlust]

Re: Johnson raw water pump just won\'t prime - new impellers

If it is the same belt driven pump as my Yanmar it could be wear in the drive shaft/lip seal. My pal lost his water flow and ended up on a beach because of this! I have just stripped mine and found lots of wear in the shaft. I was having problems getting mine to prime. I had to prime by hand and give lots of revs to get flow. Just rebuilding at the moment with new bearings, shaft and lip seal

 

[Adamastor]

Re: Johnson raw water pump just won\'t prime - new impellers

I've had the same story as Wanderlust. Replacing the cover wasn't even an option- lapping with 400' waterpaper worked a treat and cost nothing. The seals are an insidious problem: the .2mm tolerances shouldn't affect priming too badly. I had really bad experiences with a Volvo MD11C's pump, and eventually the waterpump proved to be leaking water into the casing, and air into the pump-chamber!
Good luck!

 

[No Regrets]

Re: Johnson raw water pump just won\'t prime - new impellers

Clearly the impellor IS the problem then.

It's the only variable. I suspect your engine may have had a different water pump fitted at some stage. Have you asked the agent if he has any knowledge of this?

I guess you have...you seem pretty logical so far.

In which case, if you're SURE the size is the only difference, and the inner drive surface is identical, it would be easier to skim the 0.2mm off the water pump, and secure an easy time next time you order an impellor!

 

[Poignard]

Re: Johnson raw water pump just won\'t prime - new impellers

Maybe a call to the UK subsidiary/agent of Johnson Pumps web page might get you an answer.

 

[PCUK]

Re: Johnson raw water pump just won\'t prime - new impellers

Have you tried priming the pump with water prior to starting? Once full of water and pumping it should remain OK. My pipe-work is arranged so that the pump retains water when stopped.

 

[Poignard]

Re: Johnson raw water pump just won\'t prime - new impellers

[ QUOTE ]
the key issue is that the old impeller STILL WORKS1

[/ QUOTE ]

Sorry! Missed that bit.

[memo to self: read posts before replying! /forums/images/graemlins/frown.gif]

 

[cliffordpope]

Re: Johnson raw water pump just won\'t prime - new impellers

I had a similar problem the first time I started by new Yanmar, and the advice received was:

If the pump is below the waterline then it should prime simply on opening the sea cock, as long as it is sufficiently worn - ie there is a clearance around the impeller so that incoming water can displace the air, rather than simply backing up against an airlock. In these circumstances you should not pack it with grease because .

If the water pump is above the waterline then it will not self-prime, so you need either to pack it with grease or arrange the inlet piping so that water always lies in the pump, and of course you need to prime it the first time.

 

[nedmin]

Re: Johnson raw water pump just won\'t prime - new impellers

Have you fitted the round rubber seal to the impeller,its about 5/8th of inch in dia.and pushes into the impeller.(same dia. as driveshaft)

 

[wotayottie]

Re: Johnson raw water pump just won\'t prime - new impellers

Is the Johnson pump the same as the Yanmar one? Have you tried a Yanmar impellor?

The pumps wont prime if there is a gap at the side - I had that problem with my Yanmar 2GM and had to have the pump re-furbed.

 

[timmfive]

for possible solution, see here:
http://www.ybw.com/forums/showthread.php?p=3098485#post3098485