V-P 2020 water pump corrosion

[Cantata]

Has anyone had a problem with the inside of the cover plate on the sea water pump of a Volvo 2020 corroding?
Here's the story....
Friend of mine has a Bavaria, V-P 2020, with a 120S saildrive. It's nearly 3 years old. Because he paid extra for a 3-year engine warranty, he has had to have V-P service it each year, rather than do it himself. He changed service agents this autumn because he had problems with the first people.
On the recent service, the new engineer found deep pitting on the inside of the (brass?) cover of the sea water pump. Looking more closely, he found pitting on the outside too. Obviously the first engineer had noticed the pitting, and reversed the symmetric cover, after scraping off the green paint first!
This pitting is something of a mystery.
I also have the same engine and saildrive unit in a 7-year old Moody, without any sign of this problem.
Incidentally, for those that may not know, the saildrive is made of ally, and is electrically isolated from the engine block and has its own anode.
Now...
the one difference between his engine installation and mine, is that mine has a hull anode, connected to the engine block, and his has not.
So we are wondering if this is electrolytic action that has caused the pitting. At the moment, Volvo are still saying this should not be the case.
So... anyone out there seen this before, please?

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[david_bagshaw]

in short yes, pitting occurs on the plate in the "corners"where the impeller legs bend over the cam. On Jabsco, johnson and sherwood pumps I have used. I personally assume this is impingement attack from water moving along the impeller lobe as the lobe mounts the cam.

I have noticed the brassier outer plate seems to be more vunrable than the inner casing, which is bronze, although when there is a inner wear plate also brassy coumpound the same seems to happen

Pitting occurs in under 200 hrs but doesnt apear to degrade the performance too much.

However this is only my opinion after 35 years of winterising our various engines Ii could well be wrong

<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[Trevor_swfyc]

Cavitation can cause pitting where the inlet is restricted in some way. Poor quality brass could also cause it, why not get another plate and see if it happens again.
Mine was highly polished by the impeller but was badly grooved, the grooves were removed by grinding the face down which worked for me.

Trevor

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[mikeperkins]

Re: V-P 2020 water pump corrosion
I have experienced this problem and indeed it is caviation due to the inlet restriction, take a look at the in line filter and you will likely fond it is blocked. I now inspect the raw water inlet filter before every trip and no longer have this problem.
Mike

 

[pvb]

Now... the one difference between his engine installation and mine, is that mine has a hull anode, connected to the engine block, and his has not.

Why have you connected a hull anode to your block when the engine is supposed to be electrically isolated from the saildrive? Might this not lead to accelerated electrolytic action on the saildrive?

 

[vyv_cox]

I suggest you inspect the pits using a magnifying glass. Corrosion pits will contain some corrosion product, usually a green colour with brass. Cavitation is a mechanical problem and its pits will be bright, often deep, without corrosion product. It can occur that the nascent surface can be susceptible to corrosion but in this case any corrosion product would be at most a very thin film.

Your hull anode is doing nothing for you. An engine cannot be protected by an external anode and, in the case of a saildrive, it will not protect the stern gear.