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Thread: Yanmar Water Pump Problem

  1. #1
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    Default Yanmar Water Pump Problem

    I started the old SB12 Yanmar motor in my sailboat today. It fired right up but there was no water coming from the exhaust. This is a raw-water cooled engine and for running it on the land I disconnect the ocean side of the intake hose and drop it into the small bilge. Then I run a garden hose into the bilge, keeping the through hull valve open to allow for any overflow.
    I attempted to prime the pump by putting the hose nozzle right into the seawater intake hose to get the pump going. With the garden hose removed, this worked for a bit, then stopped. I started checking things.

    All the hoses are clear and with the output hose on the pump removed, there is no water coming out of the pump unless I connect the hose to the seawater intake hose, then I get some pressure, but not much. The flow stops after a minute or so if I remove the hose and drop the intake line into the bilge. There do not appear to be any leaks on the ocean side of the pump.

    The impeller and gasket are new just installed. With the cover off the pump, I turned over the engine by hand and the impeller is turning. The cover to the pump is quite worn and last season I used it flipped over. I ran it both ways today and had the same issue on both sides. What could be causing this lack of pressure?

  2. #2
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    Default Re: Yanmar Water Pump Problem

    Is there any likelihood of a blockage somewhere in the cooling circuit? If not, and the ends of the impeller blades are contacting the pump housing, I would be looking at the sides of the impeller to make sure they are sealing properly.
    There is nothing quite as permanent as a good temporary repair.

  3. #3
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    Default Re: Yanmar Water Pump Problem

    There is zero chance of a blockage as I have the output completely disconnected from the motor. The input side was disassembled and checked - fully clear. The impellier is new and the blades fit well. I'm very suspect of the cover, which does have some wear and I've read that this actually is called a "wear cover". There is a wear tollerance of 0.02mm, which I think I exceed on one side. The other side is not too bad. It is possible that I had it misaligned (rotated) and this left some gaps. I'm going to have another look at that tomorrow. A new cover is only about $25 from TOAD with shipping, but I'd like to know for sure that this is the issue before I throw parts at the problem.

  4. #4
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    Default Re: Yanmar Water Pump Problem

    Is the impeller installed the correct way? With the vanes oriented properly according to the rotation?

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  5. #5
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    Default Re: Yanmar Water Pump Problem

    I was not aware that they had an orientation. It is a new impeller, so the blades stick straight out (an older one would have a set). If you're correct that there is an orientation, how do you tell which way to put the impeller in?

  6. #6
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    Default Re: Yanmar Water Pump Problem

    Is the impeller the same brand and model number as the previous one? It sounds very suspect.
    -Dave

  7. #7
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    Default Re: Yanmar Water Pump Problem

    Yes , I'd want a double check that the impeller is correct, plenty of compression on the vanes.
    The wear plate is worth replacing as a matter of course , I'd do that anyway.

  8. #8
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    Apr 2017
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    Kailua, HI
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    Default Re: Yanmar Water Pump Problem

    Re: post #5, sometimes there is a "top" and a "bottom" to an impeller, where there is a ring of rubber to make a seal near the hub on one side but not the other, thus, there is an upside-down orientation possible. Yes change (or mill) wear plate. Also yes check to be certain OD of impeller is right, the proliferation of non-OEM replacements means sometimes the impeller fits, but not with enough interference with outer pump edges to get a good priming seal. Also, harder or softer compounds for the rubber matter, for example the Globe urethane replacement impellers are a marvel of durability if the fit is good (they can run dry for 15 min) but they are stiff, and if not a good fit they dont prime well. Assemble with appropriate grease or lube. Good luck, these sorts of challenges with older engines can be a trial, I feel your pain!

  9. #9
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    Jul 2013
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    Default Re: Yanmar Water Pump Problem

    Does this pump have another wear plate on the inner side of the chamber? A sort of keyed washer, you might have to remove the cam to get it out.

  10. #10
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    May 2012
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    Default Re: Yanmar Water Pump Problem

    Try putting the garden hose into the pump intake underwater, and then remove it whilst still underwater. Sounds like you are getting air in there.

  11. #11
    Join Date
    Mar 2007
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    Default Re: Yanmar Water Pump Problem

    I was not aware that they had an orientation. It is a new impeller, so the blades stick straight out (an older one would have a set). If you're correct that there is an orientation, how do you tell which way to put the impeller in?
    It is usually a clockwise rotation.( check for your engine/pump).

    Yes to all all above: doing this job, you should realy change the wearplate, gasket(s), etc.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  12. #12
    Join Date
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    Norwalk CT
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    Default Re: Yanmar Water Pump Problem

    is the cam at the bottom of the impeller housing worn? If the cam gets worn down too much it will impede the flow of water.

    And check to make sure that the impeller is installed correctly. Some have a front and a back....

  13. #13
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    Oct 2017
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    windham , nh
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    Default Re: Yanmar Water Pump Problem

    After getting all of your comments, thank you, and sleeping on the problem last night, I had a plan for today. First measure and inspect everything. Here’s what I found.

    I have three impellers. All are Yanmar #104211-42070. The two older ones, which are damaged and are only carried as emergency spares, measure 19.00mm and 19.05 across the body. The new one measures between 18.85 and 19.00. Measuring these is a bit tricky as any compression of the rubber throws the measurement off.

    I measured the depth of the pump body using the extension of a caliper, which is probably not super accurate but the only method available. The depth varies from 19.85mm to 19.00 depending on where you measure. Apparently wear in the pump body is not even. It is worn more up by the cam. (Would that be consistent with deformation of the impeller blade putting additional pressure, hence wear, there?)

    The gasket is 0.30mm thick. The wear on the original side of the cover is about 0.20mm to 0.30. My methodology to check this was not super good, a feeler gage under a straight edge, but I think it demonstrates the cover is worn past specification of 0.20mm of wear.

    Based on this information I cleaned up the new/outside of the cover. What marks were there from using the cover reversed for at least one season were easily removed. I then installed the new impeller and put on the cover, new/outside in and sealed it with Permatex Form-A-Gasket. I did not use the paper gasket. I noted that with the impeller fully pressed into the pump body, the rubber extends a small amount past the pump body even though the body depth is greater than the depth of the impeller. I assume the impeller expands a bit when it is compressed into the pump.

    Upon completion of reassembly, I tested the pump without the hose to water jacket connected. The pump failed to prime but would pump if you primed it with a hose. I then connected the hose that runs back to the water jacket. Again, the pump did not prime but it pumped normally once I primed it with the hose.

    I think this demonstrates that this pump is fairly worn out. It’s still working but barely – though it has been working “barely” for a long time and has work flawlessly when in the water.

    This brings me to my last question. I measured the depth of the pump in the boat relative to the water line. The pump is at least ten inches below the waterline. This means that, when the boat is in the water, the pump never needs to be primed. Can I assume that, when in the water, the pump is going to operate reliably? I don’t really have any need to run the motor on the land any further.

  14. #14
    Join Date
    Jul 2002
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    usa
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    Default Re: Yanmar Water Pump Problem

    When I run my yanmar for the pre-season check, I connect a piece of hose to the intake hose which I remove from the through hull and run it up to the cockpit. I install a funnel to the hose and fill the funnel from a garden hose. I’m not sure even a healthy pump would suck water out of the bilge. I don’t force feed the engine, I just keep the funnel topped off.

    can you take the exit hose off the pump and see if your getting consistent water out from that point?
    __________________________________________________ ________________________

  15. #15
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    Default Re: Yanmar Water Pump Problem

    I'd say its going to work but it sounds like might be time to rebuild the pump.
    images (2).jpeg
    The compression plate above the seals is another wear item. It's quite possible that is past its use by in your pump, it's common to have some size variation available.
    If you do rebuild the pump make sure you check the seals and remove the spring steel compression rings if present , replace them with O rings.
    Why anyone would sell a pump kit with steel springs in it is beyond me but they do. They'll rot out in a year or two damhik.

  16. #16
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    Oct 2017
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    windham , nh
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    Default Re: Yanmar Water Pump Problem

    I'll look into this, John. Wherever they put in there has been there for 43 years, so I suspect there are no steel springs. I assume this repair kit does not address wear in the pump body. Can you provide the part number for this kit? I'm having trouble finding a kit that includes the cam.

    How difficult is it to remove the pump from the motor? It looks like three bolts and it pulls right out. Is that accurate?
    Last edited by Cinderella; 05-07-2021 at 06:50 PM.

  17. #17
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    Default Re: Yanmar Water Pump Problem

    I don't have a number , never owned a Yanmar myself. But yes , my expectation is just unbolt it .
    I'm saying to check any new kit for steel springs if you do that.

  18. #18
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    Oct 2017
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    windham , nh
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    Default Re: Yanmar Water Pump Problem

    OK, thank you. I'll keep a lookout for a rebuild kit with the cam, these seem a bit diffibult to find. I can probably ask TOAD if they can get one. This would be a good project for next winter. I know a guy who could machine 1mm of the face of the pump if it too worn internally. I think the current arrangement will work for this season.

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