Yanmar Raw Water Pump Questions

[Homer Shannon]

My old Yanmar SB12 has been losing water pump suction. Although the pump works fine when the boat is in the water, the pump can no longer draw water up from a hose-filled bucket when the boat is out of the water.

I have checked the inlet, output, impeller, and pump cover. All are in good order. The engine does not overheat. I suspect my problem is a worn cam lobe. I can purchase just the lobe for about $40. For about $80 I can get a complete rebuild kit with the lobe included. Note that at this time, I am not having any other issues with the pump. Before going further, I’d like to get a bit more information about rebuilding these pumps.

First, how difficult is removing the cam lobe from the pump housing? I know it is only held in by a single machine screw, but should I anticipate that this is going to be frozen and have to be drilled out? (It looks like a stainless fastener into a bronze lobe.)

Second, is the pump above or below the normal oil level in the motor? If the motor is topped up with oil (it is), can I pull the pump off without having oil run out all over?

The answers to these two questions will help guide my decision – just a lobe or a full kit.

[Lepke]

The pump is above the oil level. Once the impeller is out, you have access to both ends of the retaining screw. Use a penetrating oil on both ends. When you reassemble, use a thread coating like never-seize and you won't have to worry about removing the screw next time.
I'd buy the complete kit. Rebuilding the pump is easy. There's probably a YouTube video.

[Uncle Bob]

Originally Posted by Homer Shannon

My old Yanmar SB12 has been losing water pump suction. Although the pump works fine when the boat is in the water, the pump can no longer draw water up from a hose-filled bucket when the boat is out of the water.

I have checked the inlet, output, impeller, and pump cover. All are in good order. The engine does not overheat. I suspect my problem is a worn cam lobe. I can purchase just the lobe for about $40. For about $80 I can get a complete rebuild kit with the lobe included. Note that at this time, I am not having any other issues with the pump. Before going further, I’d like to get a bit more information about rebuilding these pumps.

First, how difficult is removing the cam lobe from the pump housing? I know it is only held in by a single machine screw, but should I anticipate that this is going to be frozen and have to be drilled out? (It looks like a stainless fastener into a bronze lobe.)

Second, is the pump above or below the normal oil level in the motor? If the motor is topped up with oil (it is), can I pull the pump off without having oil run out all over?

The answers to these two questions will help guide my decision – just a lobe or a full kit.

I would rebuild it with the kit, murphy's law dictates that as soon as you fix only one part the next part will fail.

[Homer Shannon]

I can go and get the pump off the motor any warm day and bring it into the shop.

I've noticed that the rebuild kit includes sealed bearing. If the existing unsealed bearing are still good after 43 years, should I install the new, sealed ones? I could get the sizes off the seals and just find new ones, reusing the old bearings. Cost is not an issue on this, but I wouldn't want to replace old, perfectly good bearings with new ones of unknown quality.

[Bycrick]

Before you order rebuild kits, check to see if the inside surface of the pump is worn. On some Yanmar pumps the rear cover is sealed by an o-ring seated in a groove in the pump body. When the pump inside surface wears enough, the o-ring won’t seal.

[vpbarkley]

Just wanted to ask if you primed the pump first?

Rubber impeller pumps are technically self priming. This is true when they are new.

But with wear you will find it needs to be primed. This is the case with our Yanmar.

If you can pass air through the pump it will won't prime.

I plan to replace our pump. It shows considerable wear with around 900 hours of use.

[sailcrazy]

Following. Has anyone contemplated eliminating the impeller/stock pump with something like a March (indirect drive, AC elect) or a 12VDC diaphragm pump? Access to our salt water cooling pump is a real PITA! Near impossible! Replacing the impeller is a real trick! I've read where some have used that idea on their genset salt water pump, but never heard anyone doing it on their prime mover/Yanmar diesel?

[Wotname]

Originally Posted by Homer Shannon

I can go and get the pump off the motor any warm day and bring it into the shop......

This is certainly the best way to the best possible rebuild. It gives you the time to fully inspect all the wear components - cam, seals, bearings and shaft surfaces etc. Repair / replace as necessary without the pressure do get the job finished before you leave the boat or some such other pressures.

Originally Posted by Homer Shannon

....I've noticed that the rebuild kit includes sealed bearing. If the existing unsealed bearing are still good after 43 years, should I install the new, sealed ones? I could get the sizes off the seals and just find new ones, reusing the old bearings. Cost is not an issue on this, but I wouldn't want to replace old, perfectly good bearings with new ones of unknown quality.

First up, the old bearings won't be "perfectly good". They might be serviceable and they might be good enough for the next year or only the next (say) 50 hours. Without specialist lab quality test equipment, you won't be able to know for sure. No bearing however good, has an indefinite life.

All well manufactured bearings have the manufacturers name on the bearing case. Google will tell you more about the manufacturer but any of the big names will be more than suitable for the light loads on a small raw water pump.

Here are few in no particular order but there are others.

SKF
NSK
NTN
TIMKEN
FAG

I would never use a 'no name' bearing!

[Jim Cate]

Wottie, are Yanmar pumps the usual Jabsco or Johnson pumps rebranded?

Jim

[Bill Seal]

If you want to, you can just pop the seals off. Maybe on the engine side so it gets oil.

[Mike Banks]

Those Johnson pumps need to be primed by a little water remaining in the pump. If you have replaced the impeller, you need to pour some freshwater down into the pump from the raw water strainer . That is how I do it. I also use a little vegetable oil on the impeller blades when fitting.

[Homer Shannon]

I might be able to get the pump off the boat tomorrow. I've had some time open up and weather looks petty good.

As for priming, I had issues with it priming going back a few season but it wasn't too bad. Last spring is when I realized that it would not prime at all. However it ran fine all season when the boat was in the water as the pump was below the waterline. This fall I could not get it to pump reliably. The only way to get water into the engine was to put garden hose nozzle right into the intake hose and turn the water on. This was fine for running the engine but proved impossible to get a good load of anti-freeze through the engine. After shutting the motor down, I pulled the impeller out (I do this every off season) and drained the cyliner using the petcock on the side of cyliner. I don't think my anti-freeze will protect the engine, so I'm going with drying it out.

It will be interesting to see what the thickness of existing cam lobe is and compare it with a new one. I am concerned about the new bearings. If the old ones are plain bearings that are lubricated by the motor oil, why would I want to switch to a sealed bearing that relies on its internal grease?

[Wotname]

Originally Posted by Homer Shannon

I might be able to get the pump off the boat tomorrow. I've had some time open up and weather looks petty good.

.......... I am concerned about the new bearings. If the old ones are plain bearings that are lubricated by the motor oil, why would I want to switch to a sealed bearing that relies on its internal grease?

The manufacturers make sealed bearing because "one size fits all". By this I mean, the customer can choose to keep them sealed or pop the seals off (one or both) and run them unsealed. Your choice. The seals pop off in seconds with a thin blade screwdriver or equivalent.

You might like to to remove the seal on the engine side but keep the seal on the other side or you might keep them sealed or...

Me - I keep them sealed because I know that is good enough and I need not worry about whether the engine oil is getting to the bearing or not. YMMV.

OPPS - I now see that Bill Seal has already posted the same info upthread.

[Wotname]

Originally Posted by Jim Cate

Wottie, are Yanmar pumps the usual Jabsco or Johnson pumps rebranded?

Jim

YES, at least they are for everyone I have ever seen are.

Depending on the year, place of manufacture and destination country, they will be a Jabsco or Johnson.

In Australia, the raw water pump is often added after arrival from Europe or Japan; this allows Yanmar to claim they are 'assembled' in Australia - presumably for some tax or other benefit or so I'm told.

[Seymore]

Here, there is a Yanmar 3GM30F-YEU. The raw water pump was not working, there was no water coming out with the exhaust. A knowledgeable friend dissembled the pump after repairing the heat exchanger. He found that, on the almost-new rubber impeller, the rubber was slipping on its bronze base, so that, while the shaft and base were turning, the rubber was not. He replaced the impeller with a new one, and there was lots of cooling water in the exhaust.

I would never have found that. The impeller looked good with a cursory glance. I would have gone after a plug in the water intake or hoses.

Maybe that's the OP's problem. He should try replacing the impeller with a new one, no matter what its condition seems to be.