A-4 Pump

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Servicing the Raw Water Pump for the Atomic 4 Engine

First of all I’d like to say that I have no prior experience with marine inboard engines. Being faced with the need to confront my original 30 year old water pump (original on my 30 hp Atomic 4 inboard). I, like so many other sailors, chose to save money and tackle the job myself. Actually, I never know if that’s my true motive or if I’m intent on learning to deal with these things so I don’t feel so helpless when something breaks or stops working.

Well anyway, Michael Lehmkuhl suggested that I share my pump rebuild experience as part of the FAQ section of his website, so here goes. I will describe in detail my experience and then summarize in a short step by step so you won’t have to continue to reread my droning on about my experience when you actually are doing the work.

As you probably already know there is a plethora of information out there on the Universal Atomic 4 engine. One of the gurus is Don Moyer of Moyer Marine, Inc., Harrisburg, PA Tel: 717/564-5748. A good website for the A-4 is www.ourworld.compuserve.com/homepages/Alberg30/A4contrib.htm. I was even able to download a copy of the original engine maintenance manual shich included photos of the engine from different views.

Everything I read about routine maintenance of Atomic 4 engines stated that the water pump impeller should be changed yearly. In time, the rubber impeller blades become hard and brittle and can break off and get pushed, through the water hoses, into the engine, or stop pushing enough cooling water to maintain proper engine temperature.

During the years the A-4 engines were built, three different water pumps were installed ; two different Jabsco, Sherwood and Oberdorfer brands all using different impellers. Apparently most originals, if replaced, were replaced with the Oberdorfor M202-3. Upon learning this, I assumed that was what I had, therefore I ordered a rebuild kit from Depco Pump Co. in Clearwater, Fla., 1-800-445-1656, which included the impeller, retaining ring and two seals which go over the impeller shaft. These folks were a great source of information and advice, friendly and very willing to share any knowledge. Talk to Jim in Sales/service. Jim even sent me a diagram of my pump, which helped tremendously. (NOTE: This is a SHERWOOD Pump).

When I unscrewed the cover plate of the impeller chamber, I realized it looked nothing like the replacement I bought; different number of blades and quite frankly I didn’t know how to remove the old one. Fortunately the Sherwood brand was stamped on the cover plate, so I called Depco and they were able to send me the proper rebuild kit. Jim at Depco talked me through the whole process of removal and what to look for when I did.

If you’re just planning to replace the impeller you may be able to do so by removing it’s cover plate and pulling the impeller, attached to it’s shaft, out of the pump housing. I’ve seen drawings showing removal of the impeller while the shaft is still inside the housing, but you would need to pull the shaft out far enough to access the set screw or drift pin holding the impeller on the shaft. The Oberdorfor impeller is held on it’s shaft by a retaining ring;; you know the kind that you need a retaining ring plier to remove. You may find that, due to limited access and visibility, the easiest thing to do is to simply remove the whole pump. All the different pumps were mounted to the engine with only two 9/16" bolts. Removal also allowed me to bring my pump home where I had more tools and a vice and a better sound system. Prior to removal, you will need to unclamp and plug the water intake hose going into the pump since head pressure will continue to force water from beneath the boat. I suppose you could rig some fancy coupling/cap device but I simply plugged it with a cork and duct tape.

At this time I’d like to point out a word of caution. Since the engine is mounted above the bilge, I would recommend placing a rag, pan, cardboard box or anything under your work, which would catch falling tools or, heaven forbid, mounting bolts, gaskets, etc. from falling into the abyss of your bilge. Trust me on this. I spent some time retrieving a pair of pliers from my oily, filthy bilge. Fortunately, access to the bilge from the removable cabin floor hatch improved my chances greatly.

I was advised by the pump experts, that upon removal of the impeller shaft, if I observed any pitting or scoring that I should plan on replacing the entire pump. Apparently, if you were to buy a new impeller, seals, gaskets and shaft, it would cost more than buying the entire unit. Fortunately my shaft was in good shape but removal of the innermost seal was a problem. It seized itself onto the inside wall of the pump housing. As luck would have it I recently read an article in the August issue of Sail magazine (page 40). It explained how to insert new seals by placing the seals in your freezer in order to contract the metal of the seals and heating the pump body with a propane torch to expand the walls of the pump. I tried this for removal of the existing seal and insertion of the new ones. This method worked like a charm although it did take quite a blow with the hammer to seat the outer most seal, probably cause the pump was cooling off. The article suggested using a sparkplug socket wrench or any deep socket that fits inside the pump body and a hammer to drive the seals into place. Please note that I was told to insert the seals flat side to flat side or metal side to metal side. This will become clear to you once you see the seals. Interestingly enough I noticed that my existing seals were not installed that way. Lightly coat the rubber edges of the seals prior to insertion. The flame of the torch did remove some of the paint from the pump but since the pump is cast bronze or brass I don’t believe it matters much, but you could repaint before replacing.

Before reinserting the impeller and shaft, you should lightly coat the inside of the impeller chamber with light weight bearing grease. If your pump has a grease cup, you should remove the old and replace with lightweight bearing grease.

The last thing I needed to do before remounting the pump was to make a new gasket for the impeller chamber cover plate since the pump company didn’t have a replacement.

They told me to make one from a typical brown paper grocery bag since it was similar to the original gasket thickness. I understand you could also make one out of oilskin (an oil impregnated paper product). You simply place the paper over the impeller chamber opening and push down on the paper to make impressions where the edges and mounting bolt holes are. Another method would be to press the pump down onto an ink pad and then stamp the image onto the paper. Of course you could use the old gasket as a stencil but if it’s in bad shape this may be hard to do.

Step by Step Summary

If you don’t plan on removing the pump:

1. Place a rag under your work to prevent anything from falling into the bilge.

2. Remove impeller cover plate and inspect gasket. If in good shape reuse or make new one.

3. Slide impeller on shaft out of pump housing far enough to access retaining pin or set screw, then remove retaining ring. Note, depending on pump brand and type there may not be a set screw or pin.

4. Insert new impeller onto shaft and reinsert retaining ring.

5. Coat the inside of the impeller chamber with lightweight bearing grease.

6. Push shaft and impeller back into pump housing. Note, shaft end going into the engine is split so as to align with drive mechanism which spins the shaft so turn the shaft clockwise until the shaft seats into engine. Also note that a few of the impeller blades will bend to fit into the chamber.

7. Reinstall impeller cover plate.

8. Add grease in grease cup.

If you plan on removing the pump:

1. Remove pump by undoing the 2) 9/16" mounting bolt and inspect gasket. Replace gasket if necessary.

2. Remove impeller cover plate and inspect gasket. Make new one if needed.

3. Pull impeller/shaft out of pump housing and inspect shaft for bad scoring or pitting.

4. Remove impeller by removing set screw, drift pin or retaining ring depending on model.

5. Install new impeller onto shaft.

6. If pump was leaking from area where the pump meets the engine block, either the gasket or the seals or both should be replaced. Remove existing seals and install new ones flat side to flat side (metal to metal). Note the location of the existing seals before removing and insert new ones in same locations. Put light grease or lubriplate on rubber lip of seals only. Refer to suggested method of installing stubborn seals, above.

7. Coat impeller chamber with lightweight bearing grease and Reinsert impeller/shaft into pump housing, turning in a clockwise direction.

8. Install impeller cover plate and gasket.

9. Mount pump onto engine block aligning impeller shaft with engine coupling. Install mounting bolts.

10. Reinstall water intake and discharge hoses and clamps. You’re done.

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Last Updated 20-Oct-1998