Losing Thrust @ 5000 RPM’s

[84rzv500r]

ok those tunnels are horrible looking all those gaps should be clean smooth and filled with marine silicone.

 

[Vedner19]

So does it look like the missing sealant could be causing the issue? I’m gonna get them smoothed out and sealed up.

Also, I’ve never used impeller housing liners before. I usually replace the housing with a new one. However, this boat came with them. Has anyone had issues with these liners causing cavitation? They leave a small lip you can see in the pics. Could it be contributing to the cavitation since they’re not completely flat? Should I replace with new housings and get rid of these liners?

 

[Vedner19]

Getting ready to seal up these tunnels and I did find that the impellers are different. Don’t see how that could contribute to cavitation but are there any issues with having two different impellers?

 

[FSH 210 Sport]

It is my understanding that the boats used to come with different impellers to compensate for the different loading caused by both engines spinning the same direction. This leads to uneven loading on the pumps, so a lot of times one engine will spin faster than the other, to compensate for that a different pitch impeller is used on one side.

What is the gap between the impellers and their wear rings?

 

[Vedner19]

It is my understanding that the boats used to come with different impellers to compensate for the different loading caused by both engines spinning the same direction. This leads to uneven loading on the pumps, so a lot of times one engine will spin faster than the other, to compensate for that a different pitch impeller is used on one side.

What is the gap between the impellers and their wear rings?

Thanks for the info! I just bought the boat and he had just installed the wear rings (I’m assuming trying to resolve the cavitation issue it has) so the gap is good. I’m wondering if I should just buy new impellers housings. That’s what I normally do if they’re bad.

Do you know which impeller goes on which side? I would assume the one with more pitch would be on the port side.

 

[FSH 210 Sport]

Thanks for the info! I just bought the boat and he had just installed the wear rings (I’m assuming trying to resolve the cavitation issue it has) so the gap is good. I’m wondering if I should just buy new impellers housings. That’s what I normally do if they’re bad.

What specifically do you mean by the gap is good? In all the pics you have posted so far unless I missed them, there are none of the impellers when they are inside the wear rings. This measurement is critical..

 

[Cobra Jet Steering LLC]

the veins in the pump housing look horrible and may be part of the problem if not the problem

 

[84rzv500r]

yes port impeller has slightly more pitch than stbd... i have started to just run the same impellers and slightly depitch the trailing side of the stbd impeller if needed... im ok with 200 RPM less but more than that I will adjust...

 

[84rzv500r]

the veins in the pump housing look horrible and may be part of the problem if not the problem

I agree the stator veins are horrible and thery cause cavitation until the boat gets up to speed... I would run those till some new ones can be gotten... there are some aftermarket ones out there and Yamaha is showing april for availability...

this part was bad however it still worked once the boat was moving... you can see where the cavitation eroded the the veins after the rocjs broke out chunks.... I stuck this one back on for a few weeks as i didnt have the prototypes done yet...




this is one of the prototypes it cavitates slightly however i didnt want to cut up new ones for prototypes till I was sure everything was gonna work ok... it has actually polished up a little and has been working better...

 

[Cobra Jet Steering LLC]

ok what is the stick that is coming out from under the impeller that would also cause serious cavitation but those housings are horrible

 

[84rzv500r]

ok what is the stick that is coming out from under the impeller that would also cause serious cavitation but those housings are horrible

lol that was just a piece of grass... I agree it don't take much in there to cause cavitation... I got some mono filament fishing like wound up in one at it cavitated bad... Basicly any thing that is not just discoloration that deviates from the pumps when new will degrade performance... heck i got some new stator vein housings from yamaha a few years ago that were horrible with casting flash and miss alignment I had to clean them up with a die grinder and sandpaper cones cause they cavitated...

 

[Nightmare]

Yeah, those tunnels look rough.
I guess that is what 10 years in salt water will do?

I pulled both my pumps last year. 2011 Boat , but ridiculously low hours (11 hrs).

There was some pitting on the impellers, but the housing was smooth and the clearance on the impellers are good.
I guess I didn't take a pic of the tunnel.

 

[84rzv500r]

those look just fine...

 

[Vedner19]

What specifically do you mean by the gap is good? In all the pics you have posted so far unless I missed them, there are none of the impellers when they are inside the wear rings. This measurement is critical..

Here are some pics.

 

[Cobra Jet Steering LLC]

in the future add zinc anodes to your pumps if you are in salt water

 

[Vedner19]

Well I got the nozzles painted this morning and they’re looking better. Silicone will be here today for the tunnel.

 

[Vedner19]

Well I finally got a chance to test it today and PROBLEM SOLVED! No more issues after sealing up the tunnels. I also replaced the clean out plug seals. Thanks again for all the advice! Much appreciated!

 

[FSH 210 Sport]

Awesome!

What product did you use to seal up the gaps?

 

[Vedner19]

3M Marine Fast Cure 4200