Sherwood impeller replacement


Contributing Partner
I was trying to order a replacement O-ring and gasket for the Sherwood water pump on my M-18 engine from Torresen Marine and there was some confusion about the need for a gasket. They are checking it out and are going to call me back, but I thought I would ask here as well. On the drawing, part #2 is the O-ring and part #18 is the gasket. The gasket is between what looks like a backing plate and the pump body. My question to them was, "Is the gasket normally replaced when the impeller is replaced?"

So that is my question to you, plus, "How much of the pump has to be disassembled to replace the impeller? Do all the washers, retaining rings, bearings, etc. remain in place and only the impeller is removed from the shaft?" I've never done this before so I want to be sure I do it correctly.


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Sustaining Partner
Looks just like the Sherwood pump on my 5432. Probably is. Sherwoods kit includes the impeller, an O-ring and a gasket. The O-ring goes in a groove on the impeller housing and that housing fits flat to the backing plate which is then bolted (sandwiched) to the pump body. The gasket goes between the backing plate and pump body.

Changing the impeller is easy. Remove 3 bolts, should be 7/16" and pull straight off. Impeller usually stays in the housing. Remove impeller, clean housing. The backing plate is usually still stuck to the pump body. Gently pry it off and clean the backing plate with Scotchbrite. Make sure the O-ring area is nice and clean. Clean gasket mating surface on pump body. Install impeller in housing, place O-ring in groove and then place backing plate in position on housing to hold O-ring in groove. This will make sense when you do it. I like to put a very thin coat of RTV on the gasket and stick it to the pump body. Now carefully take the impeller housing/backing plate and fit it onto the pump body. This can be tricky as the impeller needs to "clock" to the key on the shaft while the bolts need to line up between the housing, backing plate and body. Just work carefully and it will go back together. The worst thing you can do is pinch the O-ring so pay attention. I like to prime the impeller with a little dish soap to lube it from a dry start.

Thats all, no need to mess with the shaft or anything else.