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Old 06-05-2021, 13:36   #1
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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?
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Old 06-05-2021, 15:30   #2
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Re: Yanmar Water Pump Problem

Gidday Homer,
Are the impeller & gasket standard parts? The clearance between the impeller & face plate is critical. The other thing is the impeller can seperate from the bronze bush but you said it is turning so it should be ok but the pressure on it is increased when the cover is on & water is in it.

On one water pump I did i had to remove the gasket completely & just use loctite 518 on the cover plate to get it to pump. Maybe it wears the back face too over the decades. I never checked as a new water pump wasnt in the budget.

If you use Loctite you have to do the job quickly & run the pump quickly as any loctite that squeezes inside might stick the blades if left for 15mins or so. Use a minimum amount.
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Old 06-05-2021, 15:35   #3
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Re: Yanmar Water Pump Problem

Put a bucket in your cockpit HIGHER than the engine. Your water pump may not have the "head" to draw water up as far as needed.
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Old 06-05-2021, 16:13   #4
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Re: Yanmar Water Pump Problem

If it's a new impeller, it might not be wide enough (front to back) to fill the housing and fit tightly against the cover.
Just guessing.
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Old 06-05-2021, 16:28   #5
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Re: Yanmar Water Pump Problem

I have a ysb8. I use the same procedure as you BUT I put a bucket in the cockpit and run the hose to the water pump from there. Hose filling the bucket, excess runs into cockpit drains. Never had any issues.
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Old 06-05-2021, 17:00   #6
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Re: Yanmar Water Pump Problem

The bucket in the cockpit is a good idea. The pump worked fine when the boat came out of the water, so it may just be that it can't pull the water up from the bilge - but it's done so just fine in the past.

I'm very suspect of the cover, which is called a "wear plate" in the parts diagram and the workshop manual gives it a 0.02mm wear tolerance. I'm past that on one side for sure. I'll try the less worn side again tomorrow, perhaps without the gasket, and see how that does.

A new cover is not expensive, but I'd like to fully identify the problem before I throw parts at it.
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Old 06-05-2021, 17:18   #7
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Re: Yanmar Water Pump Problem

Quote:
Originally Posted by Homer Shannon View Post
The bucket in the cockpit is a good idea. The pump worked fine when the boat came out of the water, so it may just be that it can't pull the water up from the bilge - but it's done so just fine in the past.

I'm very suspect of the cover, which is called a "wear plate" in the parts diagram and the workshop manual gives it a 0.02mm wear tolerance. I'm past that on one side for sure. I'll try the less worn side again tomorrow, perhaps without the gasket, and see how that does.

A new cover is not expensive, but I'd like to fully identify the problem before I throw parts at it.

It has to be able to pull the water up normally unless your raw water intake is higher than the pump. I too use the bucket in the cockpit method to fresh water flush the engine when returning from sea.
If it did it in the past you have a problem for sure.
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Old 06-05-2021, 17:32   #8
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Re: Yanmar Water Pump Problem

The wear plate (front cover) does wear as you know. However the rear face also wears and some water pumps have a replaceable rear face plate. I am fairly certain your SB12 water pump does not have a replaceable rear wear plate but do check as I might be wrong.

As Compass790 posts, the gap between the impeller and the wear plates are critical.

If the rear face has worn too much and it if it isn't replaceable you only have three options.
1. Buy a new pump (expensive)
2. Face off the pump body where the cover plate seats against (difficult)
3. Find a ever so slightly thicker impeller (which is almost impossible)

So no easy answers once the rear face wears too much.

EDIT - the new gasket may be too thick - it happens!
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Old 06-05-2021, 17:33   #9
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Re: Yanmar Water Pump Problem

Quote:
Originally Posted by Homer Shannon View Post
The bucket in the cockpit is a good idea. The pump worked fine when the boat came out of the water, so it may just be that it can't pull the water up from the bilge - but it's done so just fine in the past.

I'm very suspect of the cover, which is called a "wear plate" in the parts diagram and the workshop manual gives it a 0.02mm wear tolerance. I'm past that on one side for sure. I'll try the less worn side again tomorrow, perhaps without the gasket, and see how that does.

A new cover is not expensive, but I'd like to fully identify the problem before I throw parts at it.
If you need to refresh the face of a cover plate, a sheet of 600 grit wet and dry laid on a mirror or sheet glass held in place with oil smeared on the surface and lubed with a thin oil will allow the plate to be trued simply by sanding in a figure 8 until there no longer wear marks on the face. Tedious but doesn't take all that long to achieve a result.
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Old 06-05-2021, 17:43   #10
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Re: Yanmar Water Pump Problem

The resurfacing sounds like it would be worth a try on the less worn side. If that doesn't do it, I guess I'd have to conclude that the inside has worn out as Wotname mentioned. It might also be worth trying a different impeller. I think I have two spares (both used), which may have a different front to back measurment.
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Old 06-05-2021, 17:50   #11
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Re: Yanmar Water Pump Problem

When you turn engine over by hand trying gripping the impeller to see if there is strong resistance, else something may have worn out or loose.
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Old 07-05-2021, 01:04   #12
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Re: Yanmar Water Pump Problem

If you grease the inside of the pump housing and cover plate, it makes a tighter seal so it's easier to draw water on the first start.
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Old 07-05-2021, 08:54   #13
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Re: Yanmar Water Pump Problem

Quote:
Originally Posted by Homer Shannon View Post
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?

The Yanmar pump cover is designed to be reversed so if one side is worn then you can simply reinstall the cover using the other face.
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Old 07-05-2021, 10:57   #14
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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 worked 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.
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Old 07-05-2021, 15:39   #15
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Re: Yanmar Water Pump Problem

Quote:
Originally Posted by Homer Shannon View Post
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.
I won't automatically make this assumption; it may be right but I think not. However the impeller blades will expand (a bit) as they are compressed by the cam. The impeller should only be proud of the pump body by about the thickness of the gasket. It seems from your measurements there is excess space between the impeller and the rear face of the body (as well as not being parallel).

Have you tried removing the cam and pressing the impeller fully into the body and (somehow) checking for contact (or lack of) between impeller and rear face?

And work why the impeller does not seat deeper into the body. Maybe whatever is stopping it can be 'modified' to accommodate the excess rear face wear.
Quote:
Originally Posted by Homer Shannon View Post
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 worked 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.
I agree the pump is getting 'weak' which is normal after a long life (mainly due to wear in the non-replaceable parts). All pumps have a maximum lift and head which will decrease as they wear. The question becomes how much performance loss is too much.

You could do a rough and ready check of your pump; within the limits of what is available to you to do the checking. If it was me, I might try checking to see if it would prime with a zero lift and then continue to pump OK with (say) three times the head needed for your installation. Then try operating with (say) 1' or 2' of lift and the same three times the needed head. OK, it might not prime with the 2' lift but if it pumps OK after manual priming, I would be happy with that.

Once in service, you will have 'spare' lift performance (because of the negative 10" of lift in the actual installation) and spare head performance (because of the three times head test).
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