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Old 01-28-2011
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eherlihy eherlihy is offline
Learning the HARD way...
 
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Red face My experience, and a few references

In the hope that this helps someone else...

I wanted to remove the impeller on my new-to-me Universal MX25 with an Oberdorfer pump for winter storage. I removed the cover plate, and there she was. In order to more easily reach the impeller, I used a small set of pliers to pull the impeller out. Unfortunately, I didn't notice the small C clip that held the impeller to the shaft. The impeller AND the shaft pulled out nicely.

I was then confronted with the problem of separating the shaft from the impeller without the use of the C clip tool, which was at home and not on the boat. I was also concerned that the shaft removed so easily. I thought that I had previously read here, that the shaft was press fitted to the bearings. Mine simply slid out.

First thing first; remove C clip. Available tools; several screwdrivers, a ball peen hammer, several hacksaw blades, channel lock pliers, and a socket set.... I tried using a slotted screwdriver to first see if I could push the clip to expand it, and then finagle it off; no dice. Then, I tried to pry the clip off with a screwdriver. This met with limited success - I broke the clip, but removed the impeller from the shaft. How expensive could a little stainless C clip be? Answer: $6.

Now to replace the shaft; fortunately, it simply slid back into the pump, and I was able to easily realign the tang in the impeller shaft with the slot in the gear shaft. I was suspicious, because I remembered something about making a tool, and press fitting, in the link above. It seemed to me that this was far too easy.

Therefore, I looked carefully at the pump housing to see if the seals were OK. I noticed that the pump was not painted, but then again, neither was the front (aluminum) cover of this engine.

I had long ago surmised that this engine had had an old style alternator bracket, which had cracked the engine timing cover, and concluded that both the timing cover, and the water pump must have been replaced by the previous owner. One of the first things that I did after acquiring the vessel, was to replace the alternator mounting bracket, and the alternator. For more about that project, and why it's important, look here.

Back to the water pump housing, I noticed a VERY small green stain near the weep hole. "The water seal must be leaking," I concluded, and decided to rebuild the whole pump. I am now not convinced that this diagnosis was accurate, but I now have the parts should the need arise.

After I drove home, I looked through Depco's catalog, which you can find here, and concluded that I had a Oberdorfer 202-15. But was puzzled by the fact that they offered 4 different rebuild kits. I also recalled from my trip to the boat that the pump did not have a paper gasket, as shown below, but rather a rubber O ring, set into a groove in the pump housing.


- Credit image from Ron Hill's Tech Note posted at c34.org

HERE is why Depco offers 4 versions of the rebuild kit: Oberdorfer has a NEW style pump, which is why Depco uses an N prefix for the rebuild kits. The new style uses an O-ring, which is set into a groove on the fact of the pump body instead of the paper gasket (#3 in the above illustration) on a flat pump body face. The other difference is that one kit is a minor rebuild kit (impeller, clip, and gasket / O-ring), while the other is a major rebuild kit (impeller, clip, gasket / O-ring, cover plate, screws, drain plug, graphite bearing, water and oil seal). Neither kit includes the shaft.

Because I tend to be thorough (my wife has another word...), I ordered the major rebuild kit (N202M-15MJK), a shaft (8767), and an extra snap ring, aka. C-Clip (5373).

Just now, in the basement I looked carefully at the parts. I tried placing the shaft through the carbon bushing just to see how tight the tolerances were. It slid through easily. Then I tried the shaft through the lip-seals (#10 in the above drawing). This was tighter, but in no way required a press.

Here is what I learned about the M202-15 raw water pump;
  • The Lip-Seals do not require any special tool to insert the shaft (although I suspect that they WILL require the press to remove from the pump body).
  • This pump has evolved. The old style pump body has a flat face, and uses a paper gasket to seal the face and the impeller cover. THE NEW STYLE PUMP: Uses a different pump body, and is designed to use an O ring, rather than a paper gasket.
  • Many (most?) of these pumps have a cover that is only mountable with one side facing the impeller. The impeller and the shaft constantly wear against the cover. The replacement cover from Depco will allow you to mount the cover with either side facing the impeller. Therefore, if the replacement cover should wear to the point that it leaks, just flip it over.
  • Because the pump impeller is a common thing to go, you MUST have a C clip tool in your tool kit.

I believe that I may have ordered the major kit, when I didn't need it. However I will have it should the need arise.

I hope that this helps someone else learn from my mistakes.

Last edited by eherlihy; 01-28-2011 at 10:49 AM.
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