Bad PCM raw water pump?

sorry just saw the year

Did you ever find any resolution on this?

KeithOnline wrote: I think the geometric dimensional differences on the impeller are the relevant issue. This would cause several orders of magnitude more bypass leak than a leak through a thread. Has anyone seen this much variance on an impeller, or actually measured the fit requirement of an impeller in a housing?

I think your on to something here but I don't know what the answer is. If it is a Jabsco you might try contacting them,I know it was over 20 years ago but they were very helpful to me on a discontinued pump. Once again maybe you could get a genuine Jabsco impeller and see if that cures your problem. I know several years ago a member here,let's just call him Marty had a aftermarket impeller in his 60's boat that would not pump. He put in a genuine sherwood impeller and it worked,the only difference between impellers was that the genuine one had little ridges on the sides of the impeller blades, the after market one did not making the impeller just fractions narrower.
Another thing that strikes me as odd is that there are no wear plates in your pump,many of the older ones like my Jabsco and Sherwood's have a replaceable plate on one side of the impeller maybe a newer design either saves money or if it is a stainless body as opposed to a softer brass one holds up against wear better

It's been a few months since I put mine back together, so I don't remember - - is there is a key that drives the impeller?

KeithOnline wrote: I didn't pull it. I'll check, but at worst, it could be a tiny tiny source of leak through the threads, and probably nil with the screw head seated.

Tiny, tiny sources are all you need to suck air instead of water.

KeithOnline wrote: The three bolt o-rings are mainly there for an assembly aid as they are outside the sealing boundary of the main O-ring. But yes, I put them in. It does have a weep hole for the spindle pump body cover. I leak checked it, and also covered it during operation. It seems the bearing seals are fine.

What about the cam bolt o-ring and the pump housing plug?

Have you tried precharging it with water? I know you shouldn't have to.

The three bolt o-rings are mainly there for an assembly aid as they are outside the sealing boundary of the main O-ring. But yes, I put them in. It does have a weep hole for the spindle pump body cover. I leak checked it, and also covered it during operation. It seems the bearing seals are fine.

Here's a picture of how it looks installed.


I rotates CW, and the left hand port is the intake. I have it running straight to a hose and a bucked to eliminate any boat equipment (strainer, valves, HX, etc.).

I have tried three diffent impellers.


The ordignal (6-8 year old) appears to be about 1/16" taller. See picture for actual dimensions.


I cannot get either of the "new" ones to pump. When I put the original back in, I can get it to pump after priming it, but if it loses a prime, it doesn't recover.

The pump body has about the same depth as the axial width of the impeller at 1.977.


But the cover plate/spindle that goes over it has a counter bore that is close to a 1/16".
This
   

This means only the original impeller is tall enough (axially) to protrude into that cavity. The others would leave the gap. The others are offical PCM products. I assume the first one was factory OEM installed.

I cannot find any other variation between the impellers, but I'm still stumped as to why they won't work. Are they that far out of spec? What else is left?

Do you have any pics of your pump?

On the old ones, like most of us have, the pumps are designed to work with either rotation engine, but if you orient the pump incorrectly for your rotation engine, it won't pull. Don't know if that could possibly apply here.