Perkins 4108 Water Impeller Not Spinning

[Ezra]

Hi All,
I have run the engine a few times this season with no problem and then decided to change the water impeller. After I made the change there is no water coming out of the exhaust and it seemed like a suction problem after I tested with a bucket of water to be sure. I opened the impeller case open and turned the engine over quickly and could see the impeller shaft spinning but the impeller is not. Any thoughts?

Thanks
E

[Lepke]

There's a key that locks the impeller to the shaft. Did you miss that in the change out?

[Ezra]

I believe the type of Sherwood Impeller I have has the key as a thru insert already connected to the impeller, so I don't think that is the problem. That said this was the first time I opened up the impeller case on new (old) boat I purchased and I don't believe anything fell out when I removed the case but I may have missed something.

[DougR]

What Lepke said......

Every 4-108 I owned had a woodruff key in the shaft that would push out of its keyway and either get stuck behind the impeller and prevent it from seating all the way in the housing, or slip between the vanes and not drive the impeller when the shaft turned.

Turn the engine over with the crank nut until the keyway is pointing up and that will help keep the woodruff key in position while you press in the impeller.

[Ezra]

Yes apologies, it was exactly that. the woodruff key had flipped up into the vanes. I have pulled it out and am trying to slide the impeller back over the key without it popping out.
thanks for the help!

[DougR]

Sometimes it helps to scribe a line on the end of the shaft which corresponds to the center of the shaft keyway. That way you can see where the impeller keyway needs to be positioned when things are half way together and your view of the key has disappeared.....

[Ezra]

Thanks, I managed to get it in after a couple tries, but your tip would be would be a handy trick. The impeller is spinning and all seems well. Now facing a new issues as with the impeller in with a new gasket and case screwed on there is still no suction. I’m fairly sure there is no clogging in the lines as water was coming out before. Just wondering if the case is too worn to create the suction.

[DougR]

Sometimes if there is enough wear in the pump cover plate that the pump won’t prime because the air just slips past the ends of the impeller blades, but it pumps water OK. Some things to try:
- Loosen up the cover and open the thru hull valve. If the pump location is low enough this will allow water to flow to the pump and out the open cover plate. Screw down the cover and try again.
- loosen the cover plate and give the impeller a healthy shot of dish washing detergent. This can provide enough sealing to get the impeller to prime.
- remove the hose on the output side of the pump and prime water and detergent there
- flip the cover over and put the outside (unworn side) of the plate against the impeller

[Ezra]

I tried loosening the cover but impeller sits too high for the water to make it from the thru hull. I undid the hose in the outpump and primed with water and soap. Then I undid the hose from the thru hull and primed that into the impeller. I also made sure water comes out of the strainer from the thru hull. I also did healthy dose of detergent around the impeller, but no luck.
The cover and the inside look decently worn and I can’t flip the cover around due to how the bolts go in so I think I need to get a new pump or find a new case cover.

[DougR]

It’s difficult to say exactly, but seems like most or all of the cam is missing from inside that pump. I see marks on the rear surface where it used to sit. Did you remove it?

[SailingHarmonie]

Originally Posted by DougR

It’s difficult to say exactly, but seems like most or all of the cam is missing from inside that pump. I see marks on the rear surface where it used to sit. Did you remove it?

Absolutley, the cam is missing. Without it, no pumping will happen.

[Ezra]

Originally Posted by DougR

It’s difficult to say exactly, but seems like most or all of the cam is missing from inside that pump. I see marks on the rear surface where it used to sit. Did you remove it?

I did not remove it. This is a new to me (bought a week ago) engine.

[DougR]

So my guess is that the cam is mostly worn or broken away.....maybe enough to pump a bit when it had water in it, but not enough to prime.

The attached photo shows what the cam should look like. ( different pump with the shaft removed, but same idea). In your pump the cam is attached with a single screw coming in from below the housing. Remove the screw and you will see what is left of the cam.

Perhaps it’s time for a pump rebuild kit.....

[Ezra]

Originally Posted by DougR

So my guess is that the cam is mostly worn or broken away.....maybe enough to pump a bit when it had water in it, but not enough to prime.

The attached photo shows what the cam should look like. ( different pump with the shaft removed, but same idea). In your pump the cam is attached with a single screw coming in from below the housing. Remove the screw and you will see what is left of the cam.

Perhaps it’s time for a pump rebuild kit.....

Thanks for showing the image. I am clearly new at this. I do have the cam and removed it to take a clearer photo of the back of the housing. I didn’t know what the cam was…