Yanmar Raw Water Pump Questions

[Seymore]

Apologies for the phrase "water pump">raw water pump" in the first line in the above post. When I hit the Edit button the prose that came up was correct and it couldn't be edited

[Jim Cate]

FWIW:

With so few hours on the pump I'd be surprised if the cam was so badly worn, and in reality it's height isn't too critical. For issues with priming I have found that scoring or wear on the cover plate or the wear plate at the back of the chamber were usually the culprit(s). If you have not yet reversed t he cover plate that is an option and the inside wear plate is a normal replacement part. Those are where I would start my investigation.

Jim

[NYSail]

I don’t know your specific set up however on my boat the pump is just above the water line so when the boat is in the water the pump can prime itself easily and pump water. When first put in water I open the sea cock, then slightly open strainer and watch water filling it, then tighten it down…… all ready to go. When I use the bucket if I don’t make sure the bucket is high up, it has a difficult time sucking the water up…..
Good luck

[Wotname]

Originally Posted by Jim Cate

FWIW:

With so few hours on the pump I'd be surprised if the cam was so badly worn, and in reality it's height isn't too critical. For issues with priming I have found that scoring or wear on the cover plate or the wear plate at the back of the chamber were usually the culprit(s). If you have not yet reversed t he cover plate that is an option and the inside wear plate is a normal replacement part. Those are where I would start my investigation.

Jim

I dunno how many hours are on the OP's pump but he has said it is 43 years old so I'm guessing there has to be more than a few (??????).

Have I missed something?

[Jim Cate]

^^^^^

OOps! Sorry 'bout that! I have confused threads here, I fear. 43 years is pretty old, but who knows how many hours have been logged. Our original raw water pump has around 5000 hours on it, had impellers, seals, bearings and wear plates replaced, some several times, but the cam is still serviceable. I'd think that the OP's is likely ok too, and would attack the other things first... or do the complete rebuild with a kit.

Jim

[Curmugeon]

I was having a problem with my pump on a Yanmar at low revs.. no water and over heating. The mechanic suggested the impeller may be the problem. I took it out it looked fine, no broken or worn blades. I changed it anyway and now the pump works perfectly.
The only difference I found was in the softness of the blades.

[Homer Shannon]

Seymore, that's a nice thought but I've checked the impeller and it's fine. You may be right that it is NOT the cam lobe, but I'll have to do a comparison to a new lobe before I know. (Does anyone know the specification for the thickness of the lobe?)

I didn't get the pump off yesterday - too cold. Sometime in the next few weeks we will probably get a fifty degree day and I'll get the job done. No point in freezng my fingers - there's lots of time before spring launch.

[Compass790]

Originally Posted by Jim Cate

FWIW:

With so few hours on the pump I'd be surprised if the cam was so badly worn, and in reality it's height isn't too critical. For issues with priming I have found that scoring or wear on the cover plate or the wear plate at the back of the chamber were usually the culprit(s). If you have not yet reversed t he cover plate that is an option and the inside wear plate is a normal replacement part. Those are where I would start my investigation.

Jim

+1 for this.
I repaired a pump that had no wear plate on the back & was badly worn
by removing the gasket & substituting Loctite 518 to seal it. Gotta lube the impeller & start quickly after installing cover to make sure the Loctite doesnt stick the blades tho. I would have skimmed or filed the pump face if that didnt work.

[Wotname]

Originally Posted by Compass790

+1 for this.
I repaired a pump that had no wear plate on the back & was badly worn
by removing the gasket & substituting Loctite 518 to seal it. Gotta lube the impeller & start quickly after installing cover to make sure the Loctite doesnt stick the blades tho. I would have skimmed or filed the pump face if that didnt work.

You raise a good point cobber.

Some (most? / all?) of the older small single and twin cylinder Yanmar raw water pumps do not have a rear wear plate and so when the rear surface does wear (as it will), one has to get inventive in order to bring the pump back to life.

I hadn't considered using 518 as a 'filler' but maybe I should remember this technique; so far I have only ever had to remove the front gasket.

[Homer Shannon]

Compass 790, can you expain a bit more about using Loctite 518 as a filler for correcting wear in the back of the pump, please. I have reversed the cover. It was heavily worn on the original inside and now the "new" inside shows only slight wear after two season. I think I average about 70 hours on the engine per season. I don't know about the previous owners, but assuming they were in the same range, a SWAG at the hours on the pump would be about 3,000.

[Homer Shannon]

OK - nevermind about the 518. I re-read the post and see that you were just using it to eliminate the gasket. I thought you had used it to repair the inside facing of the housing.

I did take the gasket out last spring but it did not make a signficiant difference. I put the gasket back in once the boat was launched as I did not want to cause excessive wear on the cover plate.

[Compass790]

Originally Posted by Homer Shannon

OK - nevermind about the 518. I re-read the post and see that you were just using it to eliminate the gasket. I thought you had used it to repair the inside facing of the housing.

I did take the gasket out last spring but it did not make a signficiant difference. I put the gasket back in once the boat was launched as I did not want to cause excessive wear on the cover plate.

Well that surprises me that removing the gasket made no difference. The back face may be be quite worn on your pump. It was obvious on the pump i was working on. It was a Johnson pump on a Lister engine. You cannot get away from cover plate wear really AFAIK as it requires a very small clearance between both ends of the impeller.
Yes I did just use 518 to substitute for the gasket. But I'm not a full time pump rebuilder so its possible yr pump may have another problem.

[Wotname]

Originally Posted by Homer Shannon

OK - nevermind about the 518. I re-read the post and see that you were just using it to eliminate the gasket. I thought you had used it to repair the inside facing of the housing.

........

Opps, I misread it the same way. Now I correctly understand how the 518 used used.

[Compass790]

Originally Posted by Homer Shannon

OK - nevermind about the 518. I re-read the post and see that you were just using it to eliminate the gasket. I thought you had used it to repair the inside facing of the housing.

I did take the gasket out last spring but it did not make a signficiant difference. I put the gasket back in once the boat was launched as I did not want to cause excessive wear on the cover plate.

Well I would go to skimming a bit off the face of the pump if the rebuild kit doesnt make any difference. Depends on how much time you want to spend on it I guess.

[tfay412]

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 do the whole rebuild kit. I did just the impeller on my 96 Hunter 280 and the rest of the pump started leaking. Just do it right the first time.