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Impeller size

mherrcat

Contributing Partner
I want to pre-emptively replace my raw water pump impeller. I plan to purchase an impeller puller to make this (hopefully) easy, but I'm not sure what size the impeller is. Defender has a Jabsco puller that fits impellers from 1 9/16" to 2 1/4". Will this cover the size of a Universal M-18 pump impeller?

The water pump appears to be original to the engine. Anyone happen to know what the impeller size is? I kind of hate to tear something apart without having the replacement part on hand. That usually results in not being able to find the replacement part locally...
 

mherrcat

Contributing Partner
The diagrams that I find on the Marine Diesel Direct website do not appear to match the pump on my engine. My pump loks like this diagram that I found in a listing for a pump conversion kit on the site. My pump has the same two mounting clamps on each side to attach the pump to the engine block and a rounded looking front. I'll get pictures this weekend to help identify what pump I have.
 

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mherrcat

Contributing Partner
I found a spare 2 1/4" x 3/4" impeller on the boat, so I believe that is the correct size. But I have a couple of questions about the replacement procedure. Below are pics of the pump.

It does appear to be a Sherwood (duh!). The cover screws are on the back of the pump housing which might make getting to the bottom one harder. Do I need to remove the entire pump from the front of the engine to change the impeller? If so, I take it that would be done by removing the two clamps that hold the pump to the engine block. Is there some alignment process to putting the pump back on the engine block? Are gaskets available for re-assembling the pump cover or is it easier/cheaper to just make your own?
 

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Saoirse

Junior Member
I have upgraded to the same water pump (Sherwood 'New Style') for the Universal M-12 of our E26 (1987). I (carefully) replace the impellar at the begining of each season without a special tool (as Treilly says).
Do I need to remove the entire pump from the front of the engine to change the impeller? ~ No, just the bolts (of which one is circled in red on your photograph). My own procedure is this: remove ignition key, isolate batteries, close intake seacock, remove inlet and outlet hoses from pump housing, then remove housing and replace impellar and o-ring then re-assemble (remember to order a replacement impellar kit).
Is there some alignment process to putting the pump back on the engine block? ~ This pump is gear-driven, and the impellar vanes align themselves to the cam when spun by its drive shaft.
Are gaskets available for re-assembling the pump cover or is it easier/cheaper to just make your own? ~ Each replacement impellar has a replacement o-ring gasket. I replace the o-ring each time I replace the impellar. I keep 2 spare impellar kits onboard while cruising. With this upgraded pump, new hoses, intake filter, and cleaned heat exchanger, my engine operates @ 170 F with 3/4 throttle (2800 rpm).

WP2.JPG

If I have given erroneous information, please correct me.

Saoirse
Cape Porpoise, ME
 

mherrcat

Contributing Partner
I ordered a Globe replacement impeller from Defender; hopefully it comes with the O-ring you mention. I believe the "spare" impeller I found on the boat is actually the old one that was replaced, but kept as a spare because it looks to have almost no wear and the vanes do not have a "set" to them. I believe it was replaced at least a year and a half ago.

The gasket I was wondering about is for the pump cover. Is that the O-ring you mentioned? It would have to be a big (2 3/4") O-ring.
 
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