Raw water pump leak dilemma

[jen1722terry]

Hello to all the fine members!

Jenn and I are off the boat for a week doing some business stuff and mountain hiking over at our North Conway condo and I'm thinking about an issue we have with our older Oberforfer raw water pump. When our mechanic replaced our transmission last week (another long story told elsewhere on this forum) he noted a small leak from the base of the raw water pump where it meets the engine block (Universal M-25-5421, 1984). He also noted that the pump had a 2-bolt mounting flange to attach it to the engine, while the engine was originally drilled for a 4-bolt flange (probably for the since discontinued Sherwood pump). He further noted that the bolts used to mount our current pump were rather small and he felt that may be the cause of the leak.

So, the mechanic suggested we have the present pump removed and have two new, larger holes drilled and tapped in the engine to allow for two larger mounting bolts. He thought that this step, along with a new mounting gasket, would stop the leaking pump.

Sounded logical, but then I saw the old post below from "Tom," circa 2000 (pasted in below, FYI), noting that the leak may have other causes. So now I'm not quite sure what to do next. I have a brand new Oferdorfer 202-M pump on board for a spare, but Tom indicates it may not fit without some modification.

My question is: has anyone else tried to replace their older Oferdorfer pump with a new one and, if so, was it a straightforward project? Or do I have to have the new pump modified to fit on the engine, as well as having the existing holes re-tapped to accept
larger, stronger bolts?

All wisdom deeply appreciated,

Jenn and Terry


Posting from "Tom" on 12/13/2000:

My raw water pump just failed after 17 years of faithful service. I learned a lot while getting it taken care of and thought I'd share it with the board, since it could be that you're all driving around ageing pumps. I've got the Universal 3 cylinder model 25 engine, but the info is probably good for any Universal owner.
The first sign of trouble is that the starboard forward motor mount starts showing water spots and corrosion worst than the port side. This means sea water is leaking past your seals and running down the shaft. I thought at first the cover plate gasket was just leaking and replaced only that because the impellar (still original) looked fine. I've got the Oberdorfer bronze pump which is guess is a replacement for the Sherwood that some boats have. Apparently they had problems with the Sherwoods and converted over somewhere along the line. The CD parts catalog shows both.
The shaft that turns the impeller is free floating and as the years go by and the impeller wears the shaft rides forward and scores the back or inside of the cover plate. When you install a new impeller you have to smooth off the back of the cover plate to maintain a good seal. You do this by putting a piece of emery cloth or heavy sandpaper on a flat surface like a pane of glass and sandiging back and forth being careful not to tilt the cover until the scoring disappears. Since Westerbeke bought out Universal they've jacked the parts prices way up to compete with Volvo prices. The paper gasket which is much thinner than a shopping bag now costs $4. No reason to pay that, make your own out of a shopping bag, manila folder or what have you and coat both sides of the gasket with RTV gasket cement. Two different mechanics told me that's what they do even when you're paying for the gasket. Finger tighten and let the gasket cement go off over night before cranking down on the screws. As long as you're in there replace the impeller as well. It's been in there a long time even if it looks OK and you can put it in your spares box for an emergency. You coat it good with liquid detergent before you put the new impeller in otherwise it may grab the walls and tear it's new self up. Well and good, but this didn't solve my leak. It turns out the seals are almost always shot too so you might as well buy the whole kit with impeller, two seals and a gasket for $40 if you're going to tackle this job. To replace the seals you have to remove the pump from the engine and remember to close the seacock first unless you're hauled out. The seals go in facing in opposite directions so look carefully before you take the old ones out. One holds the oil in the engine back and the other holds the water in the pump inside. The outside seal prys right out with a screwdriver but the inside one is a challenge. There's no lip to get under and it's at the bottom of a two inch deep shaft. You usually wind up mangling it to get it out. This is the hardest part of the job. Check the shaft carefully for scoring. When the seals go bad the metal rubs on the shaft and scores it, then the new seals won't seal because they need a smooth surface to make the seal. My shaft was history and I ordered a new one at $ 70+. We probably should be replacing the seals every so many years so that they don't wear down enough to score the shaft, but who except Larry Pardee is organized enough to do that? Make yourself a gasket to go between the engine and the pump using the same technique as the cover plate gasket and you're in business. Here's a trick to file away: The mechanic told me that you can sometimes get around replacing a scored shaft by not seating the new seal all the way down. That way it rides on a new spot on the shaft that hopefully isn't scored and can get you in where you can get a new shaft.
Incidentally I carry a spare raw water pump with me that I bought ten years ago for $80. They are now $240. I tried to just bolt it on, but it wouldn't go. Although I bought it from an authorized Univesal/Oberdorfer dealer and the part number was correct, it turns out that some Oberdorfer pumps have an eighth inch high ring on the back rather than a smooth surface. That version will not bolt on and I had to take it to a machine shop and have it fly cut off so I'll be able to use it next time. Oh, and by the way, if you have a spare pump you shouldn't leave the impeller inside the pump for a long time in storage. One or two of the impeller fins are bent over if left inside this weakens them. Take the impeller out and store it outside the pump.
My old pump had a grease cup which I turned religiously for all these years. The new pump does not have one nor a zirk fitting. The mechanic says that they have made the seals and bearings out of different material in the new pump that doesn't need greasing. That may be, but it may be a way to tell if your spare pump is identical to the old one and whether you should be suspicious about it having a ring that makes it unusable.
Just something to worry about all winter -- or maybe you want to take your raw water pump apart and check the shaft and replace the seals. What else do you have to do? Out here in Calif we're still sailing. Say, if you go South for the winter you're a snowbird, but if you don't go South are you a "snownerd"? Happy Holiday to all on the board and I hope this helps somebody.

[JWSutcliffe]

No reason for the Oberdorfer pump to leak, other than bad seals or shaft bearings. Silly to modify the engine to accommodate that. Rebuild or replace with same pumps - yes, it is still available. I get maybe 1 drip every hour of operation.

[jen1722terry]

Thanks, Skip.

I suppose we could just replace the gasket where the pump bolts to the engine, which is where the leak is. I think it will wait until haul out, as we've had enough downtime with the tranny swap this summer.

Enjoy the rest of your September, now that the storm seems to be breaking up.

Jenn and Terry

[jen1722terry]

Clarifying this issue some more: the mechanic thought that the cause of the leak was two-fold:

1. worn shaft and/or shaft seals in the pump, and,

2. the mounting bolts for the pump (where it bolts to the engine) are too small. He thought a prior owner decided to scrap the original, 4-bolt Sherwood pump in favor of a newer Oferdorfer with a 2 bolt mount. The prior owner drilled and tapped the block to accept the Oferdorfer pump, but used bolts that are too small and therefore couldn't be torqued enough to stop any leakage that gets by the pump shaft seals. Looking at the bolts, they seem small, less than 1/4". Not something you would want to really tighten down.

So, the easiest fix may be just to swap the old pump for a new one (if it fits without modification) at haul out, rather than try to rebuild the old one now, given the difficulties of the rebuild as noted by Tom in 2000 (see my original post). Since the shaft on the new pump should not let seawater leak back to where the pump mounts to the engine, I should not have to worry about applying a lot of torque to the small mounting bolts and possibly breaking them. The rebuild of the old pump can be a late fall project up at the Nova Scotia house where I have a good home shop and a skilled mechanic living next door.


thanks again

Terry