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Why do some engines have different Oberdorfer seawater pumps than others?

And what about that cir-clip “holding on the impeller”?"

-KWKloeber Dec 2018

The first part pertains more to M-25s engines with Oberdorfer pumps than it does to later engines — but it’s interesting background anyway…
The second part pertains to all Oberdorfer pumps…..

Here’s the impeller/shaft mismatch, cir-clips stories….

Grease cups are on engines with the Ob 202M-03 and 202M-07 series pumps that were used on some of our Universals (no grease cups are on the 202M-15 and 202M-16 series pumps.)

Back in the heyday of a boat-a-day for each boat manufacturer, to meet the demand Universal bought whatever model pumps were available from whatever sources they could get them (Oberdorfer, Sherwood.). Remember that “standard” (nor even "typical")  are words that the marine industry never embraced.  Remember 1 boat/day with “X” manufacturers = Universal had a demand for a crapload of marine engines.

The engine has a female fork on the fuel camshaft (see pic below) that drives our seawater pumps (the Oberdorfer 202M-15 and 202M-16 pumps have a male tang on the end of the shaft.)  The fork accepts the male end of an optional hour meter on the Kubota tractors.  (Yes, that’s what the “pump land” on our gear covers is there for — not a cooling pump — but a mechanical hour meter for the tractor.)  


Universal Motors pump adapter plate on a 1984 M-25
      (Note female camshaft inside gear cover)

But other Oberdorfer pumps have shafts with a female fork like the camshaft.  So, to use the female-shaft M202-03 and M202M-07 pumps on some of our female-socketed camshafts, Universal fabricated a special adapter plate (seen bolted to the engine above) and a male-to-male shaft adapter (see pic below.)  

Ob M202-03/07 pump with female-to-male shaft adapter

When removing the only the pump impeller and shaft, it’s usually a simple matter of reinserting/rotating the shaft/impeller until the male tang on the shaft slips into the fork on the camshaft. But on Universals with the M-03/07 pumps, the male-male shaft adapter would remain inside the gear cover and then be misaligned when reinserting the pump shaft (the adapter has to fit OVER the end of the pump shaft AND align with the female fork.)

Because the pump body blocks the view, one didn’t know what the problem was, and blue streaks were oftentimes heard emanating from below with a purple haze floating above companionways along the dock. 


Luckily I had removed my M-07 pump first (not pulled the impeller/shaft alone,) so I saw the deal and thereafter never pulled ONLY the shaft.  One you have the shaft and adapter out, you can reinsert them together and the world is good again.

Adapters to use the M202-03/07 pump on an M-25

About the Oberdorfer cir-clip “holding” the impeller on the shaft, here’s the story….

Back in the dark `90s when I replaced the Universal Ob 202M-07 pump (w/ adapter plate, etc) my engineer-side noticed that the cir-clip on the new pump shaft was “doing nothing.” It simply made it more difficult to change the impeller, but my young-n-dumb diesel-engine-novice side said, “Before I trash this clip, I want the expert(s’) opinion(s’) on why not to do that.”

I went ’round and ’round with Oberdorfer factory techies about the cir-clip -- but none could provide a reasonable explanation why it was there:

--- "It holds the impeller in place" (Nah, not necessary -- it can't go anywhere when the pump cover is in place.)  
--- "It keeps the shaft in place." (Try again, the shaft rides against the fuel camshaft and can't "exit" the pump.)  

As determined as they were with their B.S., they couldn’t rid themselves of me or my nagging question that begged for an answer — “Why would Oberdorfer spend good money to machine a groove into the shaft and buy cir-clips — unless there’s a reason for it??”

Out of sheer frustration I suppose, or maybe to play a trick on a co-worker, they passed this idiot asking unanswerable questions, onto another oldtimer’s phone extension.  It backfired on them — he had been at Oberdorfer long enough and was honest enough to reveal the truth. 

--- "Yes you're right, it's unnecessary to have it on there and you can remove it  
...but we don't tell customers that."

Eureka! Finally the answer.

Oberdorfer must have had issues with the pump shafts coming out whilst pumps were knocked about in shipping (Wait, What? “Brown” treating a packages that way? Never.) and being thrown about in warehouses (No, really?) and the cir-clip holds the shaft in place until the pump meets its final resting place on the engine.