Why do some of our engines have different Oberdorfer sea water pumps than others, and what about that cir-clip "holding on the impeller"?

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The first part pertains more to C30's with M-25s/Oberdorfer pumps, than to M-25XPs -- but it's interesting background anyway.... The second part pertains to us all.....


Here's the impeller/shaft misalignment, cir-clips stories....


Grease cups are on the Ob 202M-03 and 202M-07 series pumps (which were also used on some of our Universals), but no grease cups are on the M202-15 and 202M-16 series pumps.


Back in the heyday of a boat-a-day per boat mfgr, Universal bought whatever model pumps were available from whatever sources they could get them (OB, SW) and made do. Remember, "standard" is a word that the marine industry never embraced. So to meet demand for engines -- remember 1 boat/day with "X" manufacturers = a crap load of demand for engines.


So, Universal fabricated a special adapter plate and shaft adapter w/ male-male ends (3 pics below) to use the female shaft (M-03/07) pumps on some of our female-socketed Universals (our cam shaft end has a female fork [see 4th pic below] to accept 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 pump -- but a mechanical hour meter for the tractor.)

25 adapter1.jpg 25 adapter2.jpg 25 adapter3.jpg

Camshaft after Sherwood pumps seize up.jpg

Camshaft_after_Sherwood_pumps_seize_up.jpg\

When removing the pump impeller and shaft, it's usually a simple matter of reinserting/rotating the shaft/impeller until the male tang on the shaft lines up w/ the fork on the camshaft. But with the Universals that had the M-03/07 pumps, the male-male shaft adapter would remain inside the gear cover and then be misaligned when sliding the shaft/impeller back in (the adapter had to fit OVER the end of the shaft AND align with the female fork.) Because pump body blocks the view, one didn't know what the problem was, and blue streaks were oftentimes seen emanating from below and a purple haze floated 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 never pulled just the shaft.


About the cir-clip "holding" the impeller on the shaft, here's the story....


Back in the dark 90s when I replaced the Universal adapter plate, male-male shaft adapter, and Ob 202M-07 pump - with an Ob 202M-15 model, the engineer-side saw that the-clip was "doing nothing." But the 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 Ob techies about the cir-clip and no one could fabricate a reasonable explanation why it was there.

--- "It holds the impeller in place" (Nope, not necessary -- the pump cover does that.) 
--- "It keeps the shaft in place." (Try again, the end of the cam shaft keeps the shaft from dropping out of the pump.) 

As determined as they were with BS, they couldn't get rid of me or the nagging question that begged for an answer -- "Why would you folks spend the money to machine a groove in the shaft and buy cir-clips, unless there's a good reason?"

Out of sheer frustration I guess, and maybe to play a trick on an old-tymer colleague, they passed this idiot along to his extension. it backfired -- he had been at Ob long enough and was honest enough to reveal the truth. Ob had issues with the pump shafts coming out whenst pumps were knocked about in shipping (nah, not UPS) and thrown around in warehouses (really?) and the cir-clip holds it all together until the pump is bolted on.


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


--KWKloeber 08:07, 15 May 2015 (PDT)