My Water Pump Impeller "Adventure"

[odaydokay]

This turned out to be a bit of a a struggle, when in fact it should be easy. When I bought this (Oberdorfer) pump from Depco, it came ready to mount with impeller installed so simple bolt on deal, replacing my old Sherwood which had failed after 30 years or so. Now that 5 years have passed (low boat usage each year, maybe 8-9 trips average) I decided to replace the impeller with one I got from Depco same time as the new pump, so a factory original type as far as I know.

So, the old one came out easily using a screwdriver to hold the shaft and needlenose pliers to pull the impeller out. Saw no broken or cracked vanes, but went ahead and installed the new one as intended. (Will keep the old one for an emergency.) Slid it onto the shaft, but “hey, what’s going on here…?” it would not go on all the way, maybe 1/8 to 3/16 left to go! Tapped it a bit, still no go. Finally, pulled the shaft out and tried to get it to go on by tapping. Still not on far enough to get the circlip on. Finally had to drive home so I could use my bench vise to tap the shaft downward and off the impeller. Greased the heck out of it, but it still stopped about 1/8” from the “stop point”. Took a block of wood as buffer and tapped with hammer and it finally went to the stop. All easy after that, but I am wondering what the heck that was all about.

I will say, in general, on these type pumps (not Sherwoods as then you must reinstall the whole pump) removing the entire shaft makes the job easier than working on it in place. But if you get an impeller like mine, you will have the same struggle I did. No amount of grease will help.

Hope you all get impellers that are friendlier than this one. There are a lot of worn machine tools in this country maybe this part came from one of them.

 

[Ralph Johnstone]

Took a block of wood as buffer and tapped with hammer and it finally went to the stop.

I'm wondering what will happen when you try to install a new impellor 5 years down the road. Hammering the impellor into place is the easy part (relatively). Pulling it out does not impart anywhere near as much force between the two mating surfaces. If possible, you should investigate the problem now and be prepared to go after the supplier if the impellor won't come off. If you've got a caliper around, take a few measurement if you can get the impellor off.

 

[Richard19068]

Interesting. Lots of people say you don't need the snap ring. I don't use it. But in your case i assume it was a clear indication that the impeller was not fully seated back on the shaft.
As with Raplh Johnstone, I would be a bit leery about having to tap it on with a hammer.

 

[Stu Jackson]

Why does anyone even consider forcing something when it should be a simple slip fit?

Just because it is a boat shouldn't mean that common sense should go out the window or portlight.

Would you try this on something in your garage? Wouldn't you ASK here first?

Ralph's right.

 

[Calif. Ted]

(Will keep the old one for an emergency.)

Toss it, I don't think you'd really want to re-use that old rubber impellor in a couple years. First, I'd take it along for comparison to buy a new impellor that didn't require a hammer to install.

 

[Terry Cox]

Our Genset came with an Oberdorfor sea water pump. Long story short, ours requires an OEM (Onan) impeller and OEM gasket. Anything else and the pump will not prime. Never had a need to hammer it on or to seat. Slides on nicely.

 

[odaydokay]

I see all of your viewpoints, but setting the impeller and the shaft in my vice without gripping it impeller flat on top, shaft pointing down required only a minor tap using a bolt somewhat smaller than the opening. Taking it off in a few years should not be any harder as I don’t imagine it’s gonna get tighter I know this is strange but the thing is pumping water just fine and I am satisfied with the result. I do think I will contact Depco about this, however. Thanks to you all for tuning in.

 

[odaydokay]

This in from Depco' tech. Makes me feel a tad better.......I guess.

I am not sure why the impeller didn’t want to go on easily. I can say all it takes for that to happen though is a burr on the shaft or a little mushrooming at the top of the shaft just above the little snap ring groove. In the past, I’ve had to take a file to the shaft to get an impeller to go on like it’s supposed to. Happy to hear the pump is working well for you. If you have any more issues, questions, or concerns, please feel free to reach out to me here in the service department.

 

[Ralph Johnstone]

Possibly, yes. BUT it doesn't mean you'll be able to get it off five years down the road. I'd suggest taking it apart now and correcting the problem rather than waiting until it's time to do it five years later when it's developed a light coating of corrosion and it's not coming off for love or money.

Your boat, your choice.

 

[StanleyJ]

This turned out to be a bit of a a struggle, when in fact it should be easy. When I bought this (Oberdorfer) pump from Depco, it came ready to mount with impeller installed so simple bolt on deal, replacing my old Sherwood which had failed after 30 years or so. Now that 5 years have passed (low boat usage each year, maybe 8-9 trips average) I decided to replace the impeller with one I got from Depco same time as the new pump, so a factory original type as far as I know.

So, the old one came out easily using a screwdriver to hold the shaft and needlenose pliers to pull the impeller out. Saw no broken or cracked vanes, but went ahead and installed the new one as intended. (Will keep the old one for an emergency.) Slid it onto the shaft, but “hey, what’s going on here…?” it would not go on all the way, maybe 1/8 to 3/16 left to go! Tapped it a bit, still no go. Finally, pulled the shaft out and tried to get it to go on by tapping. Still not on far enough to get the circlip on. Finally had to drive home so I could use my bench vise to tap the shaft downward and off the impeller. Greased the heck out of it, but it still stopped about 1/8” from the “stop point”. Took a block of wood as buffer and tapped with hammer and it finally went to the stop. All easy after that, but I am wondering what the heck that was all about.

I will say, in general, on these type pumps (not Sherwoods as then you must reinstall the whole pump) removing the entire shaft makes the job easier than working on it in place. But if you get an impeller like mine, you will have the same struggle I did. No amount of grease will help.

Hope you all get impellers that are friendlier than this one. There are a lot of worn machine tools in this country maybe this part came from one of them.

I'll tell you what I discovered with my Oberdorfer pump on a Universal M-12 engine. The rubber around the center bushing on the new impeller may have to be slightly trimmed (about 1/16") with a utility knife blade to get it to seat deep enough to install the circlip. I replaced my impeller this year and the rubber in the center of the impeller overlapped the bushing slightly. The removal allowed me to seat the impeller deep enough to install the clip. This does not affect the vanes or performance.

 

[odaydokay]

Just to add a little bit to this story, this engine had been running about 20° too hot last summer, not always but sometimes but never down where it should be at 165 to 170°.
The old impeller looked absolutely fine when I took it out, no broken vanes, no scuff no nothing. It was October and I didn’t really run the engine more than a few minutes to test it and did not use the boat after that. Over the winter, I found something I did not like, namely, that the water pump intake hose had gotten chewed up by the hose clamp at the pump end. There was never any evidence of a water leak, but then again it was on the intake side, and so water would’ve been sucked by the pump at that location and maybe taken in a little bit of air? If so, the prime might’ve been disturbed a bit off and on causing that fluctuation. Anyway, I shortened the hose a bit put the clamp back on it took my first trip last weekend with this fix and of course, the new impeller. On one leg of the trip we had to run the engine for three straight hours almost. The temperature never got above 170 at any time, and I was watching it carefully. Hard to say, which did the trick, but maybe impellers that look just fine aren’t really just fine and should be changed every three or four years depending on how many hours they’ve run or whenever the engine seems to be running hotter than it should. It’s certainly a cheap repair.

 

[Clutch Cargo]

Over the winter, I found something I did not like, namely, that the water pump intake hose had gotten chewed up by the hose clamp at the pump end. There was never any evidence of a water leak, but then again it was on the intake side, and so water would’ve been sucked by the pump at that location and maybe taken in a little bit of air?

IMHO, from what you described, the pump was sucking a little bit of air. As for clamps, I've removed every single hardware store variety slotted "jubilee clip" clamps that I find. The best clamps are of the non-perforated, worm gear type with rolled edges. This is what you will find on commercial vessels as they are stronger and provide superior, even clamping force. Trident is a good manufacturer and you'll find them at places like Hamilton or Defender.

 

[odaydokay]

I have been looking at those for a long time and have not been able to find so thanks for the tip on this. I also suspect a tiny bit of air was getting sucked randomly but at least now everything seems all good. Thanks for checking in much obliged happy fourth.

 

[Clutch Cargo]

I have been looking at those for a long time and have not been able to find so thanks for the tip on this. I also suspect a tiny bit of air was getting sucked randomly but at least now everything seems all good. Thanks for checking in much obliged happy fourth.

You will find them at Hamilton and Defender. The former is my go-to. Same to you.

 

[Dalliance]

That’s quite an ordeal to change impellers. Seems like something is not right, but I’m not familiar with that pump and can’t offer any suggestions.

What I will say is that installing a five year old impeller is not a good idea. The rubber deteriorates with age and exposure to air as much as from use. Better to install a brand new impeller and hold the old one as the emergency spare.

Personally, I change mine every other year, so the used impeller kept as the emergency spare is never more than four years old. If you stay on your five year schedule, you’re expecting a ten year life from your impeller. That may be a bit over optimistic.

 

[odaydokay]

That is exactly what I have done. The new one is working great and the old one which looks new is ready to be fitted if there is an issue.