Sherwood G7B marine pump

We're posting some information about the seawater pumps on our Chrysler LM-360 marine engines in the hope that it will save others some work finding impellers and other parts.

First, the pump was used in lots of marine applications besides Chrysler, although the LM-318 and the LM-360 is where they seem to be found more often. Chrysler made a lots of those engines in a couple of configurations but they all use this pump.

These were pretty rugged engines and there are a lot of them still in service today.

This Sherwood pump is a very robust bronze pump with a wide impeller. It is still in stock at some marine parts outlets including Defender Marine here in Connecticut. It retails for about $350 but before you buy one, take your old pump apart. The three 1/4-20 bolts that hold it together may crumble but even if they do, you can chase out the threads and replace the bolts quite easily.

I used ordinary Grade 8 steel 1/4-20 X 3/4" bolts. The original bolts may have been bronze but I'm simply not going to worry about using disimilar metals in this case. Next time I change an impeller, I'll put in new bolts.

The pulley is pressed on, which is uncommon on more modern pumps but if you want to replace just the impeller or the impeller and the cam, you don't need to remove the pulley. The stainless slotted-head machine screw shown in this picture holds the cam in place. Don't remove it unless you intend to replace the cam.

If you do an Internet search for "Sherwood G7 pump" you can go directly to Sherwood and download drawings and parts lists.

That isn't a crack on the inlet but simply a casting mark. There is a lot of bronze behind it.

While the impellers in our pumps were in very bad shape (as you can see in the photo), the inside of the pumps looked okay and we choose to simply replace the impeller, O-ring and gasket, all of which come in a kit for about $25. The Sherwood part number for the impeller kit is 10615K.

Getting the new impeller in looks difficult but it will go it. We used dishwashing liquid as a lubricant.

Note that these pumps are not bi-directional. The impeller must be installed respecting the direction of rotation so mark the inlet and outlet sides of the pump after the impeller is in place. Unlike some marine pumps, the impeller vanes will not simply reverse themselves if you try to run it backwards. In fact, if you try that, you will probably damage the impeller. I speak from experience.

The pump will go back together only one way to have the inlet and outlet sides vertical. The gasket is really thin and we used a very thin layer of Permatex gasket maker between the gasket and the body of the pump. That also helps hold the gasket in place until you can get the bolts in.

 A more expensive alternative pump

Here's an interesting item that come out of our research. The Sherwood G7 (or G7B) pump is interchangeable with a Jabsco 18940-0010 pump. They are almost identical from the outside but the Jabsco pump uses a splined shaft to hold the impeller while the Sherwood uses a keyway. Jamestown Distributors in Bristol, Rhode Island, has the Jabsco pump in stock for a jaw-dropping $619.99. Jamestown also has parts for this pump.

We have two of these Jabsco pumps and they appear to be a little better quality than the Sherwood pump but for recreational marine service, we doubt that it would make much difference.

Pump mounting on the LM-360 (and probably the LM-318) engine

If you've never attempted to remove or re-mount one of these pumps on most Chrysler 360s, you'll probably find that it isn't easy, especially on the starboard engine where the pump is on the outboard side. Chrysler fitted a bracket to the engine that matches the two tapped mounting holes in the pump. The pump can be removed easily enough with a 9/16" ratchet type box wrench, although you have to feel for the lower mounting bolt that, at least on my boat, you really can't see.

Re-mounting the pump is the difficult part. The bolt that goes through the bracket and into the top mounting hole of the pump is easy but you will spend a long time trying the get the bottom bolt through the slot in the bracket and into the pump because you probably won't be able see it. You can save a lot of time by simply removing the mounting bracket from the engine (two 9/16" bolts, one about six inches long), mounting the pump to the bracket and then re-mounting the bracket to the engine. On my engines, this is a little tricky (because of that very long mounting bolt) but it will go back on. Then, attaching the inlet and outlet hoses is (fairly) easy. I smear a liberal amount of dishwashing liquid on the inside of the hoses to make them easier to get back on.

The installation I described here was on my engines, which are mounted on v-drives. That means that my engines face backwards, giving me quite a lot of room to work on the pumps. If your engines are mounted conventionally and are up against a structural member or are under the sole in a cabin, removing the mounting brackets with the pumps still attached will be much easier.