Raw water pump issues on Yanmar 2gm20f

[topmast]

A plastic bag sucked into the thruhull could be an instant intermittent blockage

[captlloyd]

Originally Posted by SFS

You are getting lots of good suggestions, and you are clearly thinking things through, so it should not be terribly difficult to determine where you are losing flow. I can hear your frustation. Take a deep breath, and approach this logically, starting at the beginning. Some of this you've already done, but it may not hurt to start again.

Eliminate one section of the system at a time, starting at the through hull. At some point, you will be able to determine the last upstream place that you had a good water supply, and whatever is downstream of that is the issue.

Two weeks ago, within a few minutes of startup, my exhaust water stopped completely. I anchored quickly, checked the strainer first, then went to the impeller, which was fine. Luckily, I moved backwards (upstream) first, and found my intake hose (between the strainer and the pump) was completely blocked with sand. Cleared it carefully, and viola! More exhaust flow than I had ever seen, which means the situation had been developing over some time.

Good luck.

Very good advice. Ah, life can be a bitch at times, when your boat is sinking you have more than enough water flowing and when you want it to flow it stops. Think of this as a learning experience.

[seabreez]

Originally Posted by NoQuarter79

We thought it was the gasket on the sea strainer so we replaced it and still nothing. There's water when we rev the engine, but still not sufficient. We would love to rebuild this pump but we are at anchor and don't have access to many tools and we are afraid to damage it even more

After replacing the impeller, leave the output hose (the one going to the motor) loose. Then start your motor and instantly you will have flow. If the flow is not present, stop the engine immediately and check why! Intake to the pump is the problem. Most of the time the pump is mounted below water level and you do not need to prime it. The flow of water should be enormous and not trickle. Once you have large flow, reconnect and then compare the flow coming out of the engine at your thermostat housing... should be the same. then check the flow coming out at the exhaust... should be the same flow.

[Vasana]

I had l problem like yours and found out that you must use the factory gadget it's part of the machined surface tolerance.also if the plate on the back has a Grove in it you can flip it over or resurface it with wet and dry sandpaper on glass.but you must use the factory gadget.

[DeepFrz]

I still am intrigued by your mention of damaging the shaft and having to stuff the shaft back in. I am wondering if you have broken the impeller loose from the spline that slides in on the shaft and allows the shaft to turn the impeller.

We need pictures and a complete definition of what work you have done.

[jamhass]

Originally Posted by NoQuarter79

One was in the output of the pump, the other two were in the hose coming from the sea strainer.

Sorry I didn't focus on this bit earlier, but it seriously reinforces my earlier suggestion to check the cam and its screw.

[LLizzard]

I'm not familiar with that pump, but have replaced many impellers and rebuilt many pumps. On most pumps, the cover is called a wear plate, and they do wear, losing prime. you can try to smooth the wear pattern in the plate, but I've not had much luck in that. Also, pump bodies do wear as well. Both can lower or stop pumping. I'm not clear exactly what you did to the shaft. If you damaged the keyway the impeller probably would not spin enough to pump water or break vanes. Is the cam that compresses the vanes lock in place? Is it worn?
Whatever caused the original problem, you may have more than one now that you might have damaged the shaft.
Rather than a new pump, I would take the pump off and take it to a pump rebuilder to have a look and make sure the pump is solid.

[NoQuarter79]

We have such spotty internet. I will get pictures on tomorrow for sure though. Thank you for the advice so far. All we really wanna know it's if our shaft is repairable, and again I will definitely post pictures tomorrow.

[DotDun]

It is the correct pump used by Yanmar and may be the original. How many hours on the pump? Sometime pumps just wear out. If the engine was built for the EU market, it's the pump model with a fixed cam. The fixed cam model is 1/2 the price of the changeable cam unit. I've rebuilt several of this model. Call Depco Pump, they stock both models and have all parts available.

[DotDun]

Originally Posted by NoQuarter79

We have such spotty internet. I will get pictures on tomorrow for sure though. Thank you for the advice so far. All we really wanna know it's if our shaft is repairable, and again I will definitely post pictures tomorrow.

IIRC, the shaft is not cheap ($50?).

FWIW, there is no need to remove the shaft unless the bearings need replaced. You can even change the lip seal with the shaft in place. If you are trying to get the nut off the front, it's a left-hand thread!

[NoQuarter79]

$50 is much better than $300 for a whole new pump. I was wanting to say we had a fixed cam but wasn't 100% sure I was saying the right thing. Here's our shaft and pump housing. I'm hesitant to take the impeller out because of how difficult it was to get back in.

[DotDun]

Originally Posted by NoQuarter79

$50 is much better than $300 for a whole new pump. I was wanting to say we had a fixed cam but wasn't 100% sure I was saying the right thing. Here's our shaft and pump housing. I'm hesitant to take the impeller out because of how difficult it was to get back in.

Yes, you have the pump shipped on the EU model Yanmars.

The last one I bought from Depco was $216. (128397-42500)

I've rebuilt mine several times and have probably 3 spare pumps.

There are very small nuances with pumps that cause poor performance. I used a micrometer and found even 1/2mm difference can cause big performance issues. Depending on how much wear, you might grind/sand (60 grit on a power multi-tool) down the inside of the cover to smooth, I've down that a few times and had success. Depending on how deep the lettering is stamped on the cover (no sharp edges on the letters), you may get away with turning it over. It's important to make sure that cover doesn't leak, the o-ring groove needs to be complete clean and use a new o-ring with lube.

At some point, there is going to be enough wear that saving the pump is futile, you'll need a new one. I had one pump with ~1200 hours on it that no matter what I did, it just won't pump good enough and I threw it away.

[SFS]

Originally Posted by NoQuarter79

I'm hesitant to take the impeller out because of how difficult it was to get back in.

Here is a trick to make that much easier: use a cable tie to "pre-bend" all of the impeller vanes at once (in the correct direction of course), then snug it down enough to ensure the vanes stay bent. This makes the circumference of the circle you are working with smaller than the "hole" you are fitting the impeller into.

Try to leave the tie closer to you (i.e., on the outer edge) rather than the center of the impeller vanes, so that it is easier to slide off (towards you) once the impeller partially in place. Hope that makes sense.

It really makes a tough job pretty easy.

[NoQuarter79]

It wasn't difficult the fit it in because the impeller. It's because we bent the shaft open trying to open it.

[NoQuarter79]

It might not look so bad in the pictures but we had a hard time trying to pry those shaft bars back together so the impeller would even fit over them.