320 sea water pumps

[Mike Dieterle]

Good day to everyone, we have a new to us of 6 months 1996 320 voyager with twin 350 crusaders that I am replacing the impellers on and there are no numbers of any kind on the pump housing what so ever, the only markings on the pump housing is the manufacture, "Sherwood", I found a supplier for the impellers but I when I ask for the cams they want to know which Sherwood pump I have, there are 3 pumps in that configuration that look alike but the cams are different according to the supplier. would greatly appreciate any help on figuring which cam I need to order. The boat is an hour away from me so I don't have the engine numbers at this time but I do have a pump in front of me if that would help.

[Cooler]

Morning Mike! You really need to have the engine SN # to be sure. Those numbers would probably be listed in any paper work you have from the purchase. Or, you could contact Carver with your hull#, and they would have the construction logs for your vessel. Bring the pump to a local marine store, and they should be able to match it. Those pumps are very common. Good luck & welcome to the gang! er

[Mike Dieterle]

I appreciate the feed back and I did take the pumps to two different marina shops and they both looked at them like it was the plague, I have a great marina I will be taking them to on grand and with any luck they will come up with the correct parts to do the repairs. in closing I will take a screen shot of my hull and engine numbers for next time. thank you for the welcome so far I love this group because there hasn't been any smart ass remarks like some other forums out there.

[bud37]

I am curious/nosey, just for my own info.....why are you changing the cams....are they worn badly, poor flow..? The impellers are a given.

[Mike Dieterle]

yes the cams are worn to where they have cavitation pockets so the impeller will not get a great seal to pull the water needed to feed the engine water pumps, anything below 1500 rpm there is a constant volume of exhaust water coming from the exhaust tips and anything starting above that it gets kinda sketchy. boat has 800 ish hours on it and I don't know the history very well when it comes to day to day or yearly maintenance.

[km1125]

If your cams are that worn I'd be thinking about doing a whole kit, as your seals are either also an issue or will be soon.

Your HIN should also be on your boat registration or insurance paperwork, if you have that handy.

A pic or two of the pump may help a lot. Many of the Sherwoods have unique features which identify them (like the input/output port configurations).

[bud37]

Source of the post yes the cams are worn to where they have cavitation pockets so the impeller will not get a great seal to pull the water needed to feed the engine water pumps, anything below 1500 rpm there is a constant volume of exhaust water coming from the exhaust tips and anything starting above that it gets kinda sketchy. boat has 800 ish hours on it and I don't know the history very well when it comes to day to day or yearly maintenance.

The reason I asked about the cams is that the cam itself has only one function in that pump, to compress the vanes...holds back on the inlet side to create low pressure then squishes on the outlet side to create high pressure..very highly technical terms used... ...the pump efficiency is more compromised by wear/grooves in the pump housing itself , and on the back plate and the front wear plates .....if your bronze pump housings are worn badly ( grooves), may be a different story, like KM said, some pics would be good.

When you are not sure of the history, being pro active is always the best course IMHO. Maybe a couple new pumps then rebuild the best of the two old ones as a quick change spare......I know , its easy to spend your money...

[Viper]

A worn cam will affect pump efficiency/volume. The cam folds the vanes, as the vanes exit the cam they open/strighten up. This opening up increases the area/volume between each vane which causes an area of negative pressure (vacuum) between each vane as they open up thus sucking up water through the inlet port. If the cam is worn, it won't fold the vanes enough and when they open, the difference in the area between the vanes when folded and open won't be as large hence reducing volume. A worn cam won't compress the vanes enough for pump volume to reach spec. A cam that is worn/dull at the ends of the tapers instead of sharp ends will slap the impeller as it rides on and off the cam. This will wear the impeller pretty quick and cause it to fail prematurely.

Pressure is more a factor of impeller design. More/less vanes, longer vanes usually produce less pressure but are more tolerant of debris and poor pump conditions, shorter vanes will flex less so produce more pressure but are less tolerant of debris and pump condition.

While grooves in the pump ends play a large role in reducing pump efficiency, the condition of the cam is more significant IMO. If there's less negative pressure to begin with, the grooves won't matter. Grooves or not, a bad cam will make things way worse and it's something that's often overlooked, wear plates are way easier to replace and get, cams, not that readily available!

[bud37]

Agreed if the cam is worn away very badly....yes..now in that case my guess would be the rest of the pump housing will be fairly bad and at that point total replacement although pricey is the best option considering what engines cost.....

But still, a positive displacement flex vane pump needs the end plates smooth and free of any grooves deeper than what you can feel with a thumb nail, for any efficiency what so ever....the impeller needs to make clean contact at the back plate and front plate to work properly ....

[Mike Dieterle]

Sorry for the long delay in responding back to everyone, I did find a major repair kit available for both pumps and yes both pump housing wear plates and end cap are worn to where they need to be replaced, how ever the pumps are no longer produced under that model # and have been superseded to an improved version with a lead time of a 2 to 3 weeks. I went ahead and put kits in the old pumps for now and when the new pumps arrive I will be changing them out. On a side note the kits did make a noticeable improvement. I want to a minute to thank everyone involved so much for all the helpful and useful comments from everyone, I hope you all have a great day on the water and be safe and watch out for inconsiderates.