What am I doing wrong? New impeller not working

[jonelli]

Hey Guys,
I'm attempting to do my M-25XP engine maintenance, and so my plan was to start with the cold stuff, impeller, coolant, fuel filters, then do the oil.

I'm stuck at the impeller.

I put in the new one, and no water flows out the exhaust. Figuring it was some gunk clogged somewhere, spent half the day taking stuff apart and checking for blockages not finding any. So, after scratching my head, I decided to put the old impeller back in and VOILA it worked perfect. So, thinking maybe it was a fluke, put the new one back in - no flow. Then put the old one back in - flow. put the new one back in - no flow. So THEN I figured it's gotta be a bad impeller, right? I took it back, got another one, and the replacement new one is doing the same thing - no flow. What could I be doing wrong? They look identical (oberdofer pump).

 

[The Garbone]

Did you lay them next to each other, may have different thickness.

 

[jonelli]

Yes I did. I don't see any obvious difference. I'm stumped.

 

[The Garbone]

Hmm, No idea. How does the shoe in the top of the chamber look, maybe it is worn out, don't think that is it but it is pretty much the only other part.

 

[Ralph Johnstone]

Yes I did. I don't see any obvious difference. I'm stumped.

Hard to tell from here, but just shooting in the dark:

- is the outside diameter of the impellers the same ? They look similar in the pic.

- is the ID of the impeller bushing the same as the OD of the shaft ?

- is the shaft key in place ?

- is there any wear on the new impeller bushing which would indicate slippage of the impeller on the shaft.

 

[jonelli]

They look the same as far as I can tell. I've read about some out of tolerance ones on other pumps that didn't work, but these don't appear to me to be different.

I swapped the old/new one again a couple more times, and its the same issue, the old one works the new one doesn't.

The first pic imp1.jpg is the old impeller that I'm about to take back out, middle is the pump without the impeller, and imp3.jpg is the new one I just tried again.

 

[Ralph Johnstone]

Re: What am I doing wrong? New impeller not working

They look the same as far as I can tell. I've read about some out of tolerance ones on other pumps that didn't work, but these don't appear to me to be different.

Does the impeller turn on the shaft ? ? ?

Hard to see from the photos, but is there a key against the flattened portion of the shaft with the new impeller ?

 

[jonelli]

Yes, it turns on the shaft, I cranked the motor with the cover off and watched it. The "key" at the end is not a key, its a gouge in the metal, but it's superficial and is only at the edge. It doesn't appear to affect anything.

 

[jonelli]

What about the cover plate? It does have a semi deep groove in it. Take a look at it here, you can see how deep the groove is.
I'll have to go back tomorrow, grab the cover and find someone with a belt sander.

 

[jonelli]

What about the cover plate? It does have a semi deep groove in it. Take a look at it here, you can see how deep the groove is.
I'll have to go back tomorrow, grab the cover and find someone with a belt sander.

Another thing I notice is that I do not see any washers on the new or old impeller. In this diagragm, part number 13 I do not hav.

http://www.depcopump.com/datasheets/oberdorfer/202M-15.pdf

 

[Ralph Johnstone]

Re: What am I doing wrong? New impeller not working

Yes, it turns on the shaft,

Am I correct in understanding that the impeller tuns WITH the shaft and not ON the shaft ?

The impeller must be locked on the shaft as if they are one unit. What's got me scratching my head is that when you see a flattened portion on the shaft as you have, the bushing in the impeller will also have a corresponding flattened section which will lock the two of them together. It's cheaper than machining a key way in the shaft and bushing. Almost as good, just cheaper.

As far as the gouge on the cover plate is concerned, unless it is worn to the shape of the old impeller, I can't see that completely eliminating the flow. However, if you can accurately resurface it, maybe it's worth a try. It can't hurt. If I could suggest, a belt sander is not too likely to maintain a flat surface. I would suggest powdered emery on plate glass and mixed with light oil (if you have access) as the best means of maintaining a true surface. If you can go this route, get it as smooth as you can. Mind you, for the trouble, it's probably easier to invest in a new cover plate.

Finally, if you're saying the NEW impeller IS locked on the shaft, I'm going to have to bow out as I'm fresh out of ideas.

Let us know what you find.

 

[Ralph Johnstone]

Now We're Getting Desperate ..........

Another thing I notice is that I do not see any washers on the new or old impeller. In this diagragm, part number 13 I do not hav.

http://www.depcopump.com/datasheets/oberdorfer/202M-15.pdf

............. and turning to the instructions as a last resort.

Yes, the washers must serve a purpose but you would think that the final axial location of the impeller is controlled by the rear face of the pump casing and the cover plate at the other end.

Yes, you need the missing washers, but why does the old impeller work well without the washers but the new impeller doesn't ?

So many questions, so little time.

 

[jonelli]

The impeller turns with the shaft. It has a flat side and the impeller is indeed locked in that position.
The groove gouge is pretty deep. You'd be sanding with emory, oil, and glass for three days to get that much surface down. I might have to come up with a better finishing sand process, but I need to re-surface that plate quite a bit.

I've never seen the washers as shown in the diagrams, mine never had them, maybe the previous guy lost them? Last year when I pulled the old impeller, it must've been in there for years without being changed. The guys at Captains locker said they'd never seen one that bad. But I didn't have any trouble at the time with a replacement.

I'm going to make a few calls in the morning and resurface the cover plate and see how that goes.

When I was going through all of the lines checking for clogs after installing the new impeller, I would hold a hose end in my hand, open the sea cock and have a friend crank the motor. The flow went from dribble (sea cock open) to some water flow so I assumed it was working at first. But it seems that "some water flow" is very weak pressure, and it's just not pumping through the system.

I'm going with the theory that the seals inside due to the cover plate are a likely culprit, and the old impeller is just softer and worn into the groove which is why it works okay.

I'll let you know in a couple days.

 

[Capt jgw]

You did replace the thin paper gaskets, right? The pump won't seal or pump without them.
I don't know about the washers, mine doesn't have then either. There have been a few variations of this pump over the years, must be the new ones have them but the old ones don't.
The wear on the cover plate is an issue, but you'd probably be better off replacing the plate rather than trying to machine it down. It would get pretty thin, then maybe you'd have to get shorter screws to get it on tight enough. The pump body will also wear at the back, and there's no fixing that. My pump is worn enough that the blue nitrile impellers won't work but the black rubber ones still do.

 

[woodster]

get a speed seal kit and be done with it thus eliminating the resurfacing of the old one and as much as you have taken it in an out the speed seal would make a quick change affair out of it for you

 

[markwbird]

new impeller not sealing

It seems to me that the new one is not sealing because it is not worn into the perfect fit like the old one is. Try this: Lube it up real good with a water based lube like KY. Also, flip the cover plate over so the smooth non grooved outside of the plate is on the inside. This may allow it to seal while the new impeller wears into a good seal.

 

[jonelli]

Where do you get Speedseal kits for Oberdorfers?

@Mark : Can't flip cover, it's a casting with a big raised "Oberdorfer" on the outside. A quick sanding shouldn't be hard or hurt anything more. I'll try that first. It will at least make things more evident.

 

[Jack - La Paz Mx]

Another possibility is an air lock due to a variety of conditions. Make sure the pump is full of water before starting. Using a lube as mentioned before (even petroleum jelly) helps the seal too. These pumps do pump quite a lot of water when operating. Typical of a sailboat, it tends to be something we overlook.

 

[jonelli]

Jack, I've swapped the old/new one about 6-7 times already and it's consistent to the impeller. I would think that if it was an air lock of some sort I'd see varying results, but I do not.

 

[The Garbone]

Moyer Marine sells a rebuild kit and new fronts for that pump. Even though they are a4 centric it is a great forum for issues like this.