A Sherwood Water Pump “PSA”

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oil&water
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A Sherwood Water Pump “PSA”

Post by oil&water » Sun Aug 12, 2018 8:30 am

A PSA for the group. Over the last month, I have run across a similar problem on two different boats. The Sherwood raw water pumps on our vessels are known for bearing wear issues. When they wear, the impeller blades become warped while spinning and the brass diverters inside cut the vanes up.

The first boat was a Cummins accessory gear crank driven pump. The bearing wear was so bad that when the impeller was removed, I could pull the Sherwood gear off the accessory gear with the pump fully secured. The owner received an overheat alarm while on plane, but the gauge appeared to be in normal range. There was a slight increase in temperature by a few degrees. I had figured it was a blocked heat exchanger and we were preparing to run Barnacle Buster through the system when I discovered the pump issue. Fortunately, it was replaced before the pump completely failed and took out the accessory gear and potentially the high pressure fuel pump which also runs from that gear.

The second boat was on our F-32. I had noticed a slightly hotter temp on the port engine and had steam in the exhaust. Infrared readings showed the engines operating at the same temperature at the thermostat housing. Supposedly the previous owner had the impellers changed about a year and a half ago with only about 60 hours on them. I have put another 60 on them myself. So I figured it was a gauge issue and that the steam was oil burning, which I knew was a slight problem on that motor. Fast forward a few weeks and the temp had gotten hotter than usual on a quick evening jaunt. I pulled the water pump yesterday and found a gnarly mess. The impeller was clearly older than stated and the blades were chunked up from the brass diverter. The pump was a hot mess. The bearings had dislodged and were stuck inside the housing neck in a rusted mess. The inside of the pump had extensive rust and calcium buildup. Fortunately I caught the mess before a complete failure happened. While not as catastrophic as the Cummins equipped boat, it still could have snapped belts and ripped off the fuel line and throttle cable. I had spare pumps so I will be changing this one out and rebuilding the original for later use. I am also replacing the raw water intake hose from the strainer to the pump as some degradation was noticed on the rubber outer shell.

Be sure to clean out your heat exchanger or engine passages if the impeller is damaged as those pieces of rubber have to go somewhere. If left in there, they can clog up the small passages and restrict water flow.

Moral of the story, check your raw water pumps and make sure the bearings do not have excessive wear. The impellers should be checked and replaced if any signs of wear are present. The shafts should not have any side to side play. If they do, rebuild or replace the pump. If you rebuild them, it will require the use of a press to separate and install the bearing and shaft.
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1980 Trojan F32 / 323 (sans lower helm - wet bar in its place)
Twin Chrysler M360 / Onan 6.5

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WayWeGo
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Re: A Sherwood Water Pump “PSA”

Post by WayWeGo » Sun Aug 12, 2018 4:12 pm

Great info -- thanks for bringing this content from the FB page!
1975 F-36 Convertible
Twin Chrysler 440's

oil&water
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Re: A Sherwood Water Pump “PSA”

Post by oil&water » Mon Aug 13, 2018 12:20 am

No Problem Way! Hope your boat is bringing plenty of enjoyment this year.
1980 Trojan F32 / 323 (sans lower helm - wet bar in its place)
Twin Chrysler M360 / Onan 6.5

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