Cavitation...

[ratchetdu]

So, Ive had an issue here and there with cavitiation before and usually able to get it to clear up or disappear... This time, its not going away... After 3 outings. Although does seem to be getting better/less...

Difference is... this is the first year Ive slipped versus trailering.

Ive done the usual reverse trick. Ive stuck my arm up in the clean out port as far as i can. Swam under boat and looked at intakes. Rubbed hands along grates. Felt edges of blades (they are dinged, but have been since day one 7 years ago).

Nothing there. All seems normal. I really dont want to have to put on trailer and pull the pump, but i think i'm out of options...

When i first noticed it, i went to plugs and pulled a tumbleweed from the clean out on port side. Same engine that is still cavitating? Odds are is something still there? Or should i look at pulling pump??

Also, only does it while getting on plane initially, when pulling boarder/tube, or right around 5-6K rpm then goes away. Also does it coming off plane and into slower speeds. Doesnt do it at all times... Is it OK to run if no cavitiation, just avoid those activites and rpm range for now until i pull later in season?

Sorry for long post. As always, thanks i advance for input...

 

[Ronnie]

Sounds like the tumble weed may have stripped away some of the silicone around the pump before the impeller. My 06 sx230ho had the same symptoms after I removed some debris from the problem pump. I ended up resealing it myself, first with rtv silicone as a test than with 3m 5200 or 4200. Use the good pump as a model but generally speaking the goal is to make the transitions (e.g. Between the fiber glass and metal pump parts) before the impeller as smooth as possible. I cleaned the area and filled any gaps or ridges with 4200 or 5200 and a razor blade.

 

[Beachbummer]

As extra info, without questioning anything stated previously...My understanding of 3M 5200 is that it is very much permanent. You may need a sledge hammer and saw to remove it if you ever need to. Beware, and consider it a great option for any joints that should never be undone. If you want a chance to remove in the future, 4200 is your better bet on those joints.

I don't yet have one of these boats, so I have no clue which of the joints and seals you may want to remove in the future, but if there are any such joints, use 4200 on those and 5200 on the forever ones that will not be coming off.

 

[swatski]

I would agree with @Ronnie and @Beachbummer. This is likely a missing sealant scenario, albeit you may also have some corrosion issues from wet slipping. Does not take much to get cavitation!
5200 is nasty, but it is just about the only thing that will stick around for this kind of repair. It has to be used within 24 or 48hrs of opening the tube, unless - (a brilliant tip coming up!) - you store it in a freezer in a sealed bag.

 

[ToddW850]

Agreed with the above posts. But you also mention your blades (impellers) were dinged. That too can cause cavitation, depending on the severity of the dings.

 

[ratchetdu]

Thanks guys. Sounds like I'll be pulling the pump soon. I know there is write up for pulling it, but is there one showing where to replace the silcone? I didnt seem to see those areas exactly...

Besides it being annoying, it wont hurt to run the boat? Just avoid the speeds causing the cavitiation right?

 

[Bruce]

Thanks guys. Sounds like I'll be pulling the pump soon. I know there is write up for pulling it, but is there one showing where to replace the silcone? I didnt seem to see those areas exactly...

Besides it being annoying, it wont hurt to run the boat? Just avoid the speeds causing the cavitiation right?

Cavitation can cause wear on the impellers. Excessive amounts of cavitation will reduce cooling. But is sounds like you are bot constantly in the ranges where you are feeling cavitation.

I am betting you have something in there you can not feel or a dinged up impeller.

 

[ratchetdu]

Cavitation can cause wear on the impellers. Excessive amounts of cavitation will reduce cooling. But is sounds like you are bot constantly in the ranges where you are feeling cavitation.

I am betting you have something in there you can not feel or a dinged up impeller.

Im hoping its just something in there like you say. Ill see how it does this weekend, if it goes away or not. If not I'll pull it to take a look.

 

[Scottintexas]

here is a link to my thread with pictures when I had some loose silicone causing cavitation,
it will be easy to see when you get up under there,
https://jetboaters.net/threads/cavitation-missing-sealant-in-pump-grate.884/

 

[jcyamaharider]

I used E6000 and it has held up all boating season and still looks like it did when I put it on. Much cheaper then 5200 also.

 

[ncnmra]

As an idea; perhaps pull the spark plugs and see if the impeller is rotating easily? I have seen pictures with a small stick lodged between the impeller and the housing which couldn't be easily felt through the clean out plug. This way you could see if something is jammed there, but you won't be able to turn the impeller with the spark plugs in. Ultimately, pulling the pump is your best bet though, and/or looking at it from below (snorkel?

If something is jammed between the housing, I would be concerned that it may wear away the housing over time.

 

[ratchetdu]

As an update... Went out this weekend and all seemed good. Didnt notice early on. Tried some wakeboarding and it returned under load. Back rest of day?

I like the idea to pull spark plugs and turn. I can do so with out putting on trailer...

 

[Scottintexas]

when my cavitation/loose silicone happened I was trying to pull someone off a sand bar, I was at about 8k rpm going nowhere before he finally came off,
I think the going nowhere created more suction than normally having the water forced into the jet by speed causing the silicone to come loose and probably that's why you feel it under load also,

 

[ratchetdu]

Thanks to all who helped figure this out... Pulled the pump and it was the missing silicone causing the cavitation. I couldnt really tell what areas were missing it, so i just added where it looked like it was supposed to go. It worked!!! Boat actually feels stronger and gets up faster than i can remember. Still feel a slight bit of it, but barely noticeable and not all the time. I think its just me...

Pump was a bit of a struggle to remove and put back in though. The impeller was really tight against the sleeve and took some work to get it out. Just as hard going back in, but as I mentioned running great. Next time I will be removing the bolts further back and not separating from the sleeve as someone eslse mentioned, but i didnt realize until i was finished...

Thanks again. Wouldnt have tackled this without you guys!!!

 

[Brian Howard]

Hey Guys; New User here, so excuse my ignorance. I just purchased a slightly USED 2016 Yamaha 242X.

First time out; trailered from garage to the lake. Max Speed: 7mph, tacking 3,400 rpm. Anything beyond 3,400 rpm and there is CLEAR cavitation. No weeds, no obstructions in intake, NO leak in plugs. YES I CHECKED THEM ALL....

Trip #2; *boat had sat in water at the dock for 1 full week. I got back in, and sped down the lake, NO ISSUES. Stopped for a minute, turned the auto bilge on, spun around; 7mph MAX again. 3,4000 MAX rpm.

Trip #3; Removed jet plugs, Greased Plugs, inspected impellers and intake. Then covered plugs with 3” of water (thinking It may have been sucking air from above). STILL Cavitation.

Called Previous Owner; He says they sucked a rope last year and had to replace some parts......-thanks for that...

THEORY: Is it possible (or plausible) that the problem could be the shaft seal in the hull where the impeller spins? I’m thinking this for a few reasons; 1. When the boat was sitting, if there was a leak in that seal, water could have been introduced into the hull, in small enough quantities to cause the spinning of the impeller to NOT introduce AIR from the hull, but instead the water on the hull side . After I turned on the bilge; the water evacuated, and then the air on the HULL side of the seal was able to get sucked into the impeller, causing cavitation.

PLEASE let me know if this is even a possible/plausible theory. It’s under warranty, and going to the dealer, so any advice you have as to WHAT should be replaced for this?

THANKS!

 

[Ronnie]

So you only feel cavitation above 3400 rpm correct? That is your engines will rev t9 7600ish but not without cavitating correct? Both engines are doing this? O don’t have any experience with cavitation caused by a faulty shaft seal but I think it’s possibl only because it’s in front of the impeller and the cause of cavitation is always in front of the impeller.

Other things I would check for:
Are the impellers the stock impellers and if so are they damaged or have they been repitched incorrectly? You might need a pwc shop to measure the pitch for you.
Is there any missing sealant where the pumps and hull meet? This is easier to determine when you have one good engine/pump to compare the bad one too.
Are you sure there is nothing wrapped around the shaft. All it takes is a piece of fishing line or a small twig to cause cavitation.

 

[Brian Howard]

Correct, above 3400 and above only. Correct engines Rev high but cavitation occurs. Both engines. Very close visual inspection shows no debris.

Thanks!

So you only feel cavitation above 3400 rpm correct? That is your engines will rev t9 7600ish but not without cavitating correct? Both engines are doing this? O don’t have any experience with cavitation caused by a faulty shaft seal but I think it’s possibl only because it’s in front of the impeller and the cause of cavitation is always in front of the impeller.

Other things I would check for:
Are the impellers the stock impellers and if so are they damaged or have they been repitched incorrectly? You might need a pwc shop to measure the pitch for you.
Is there any missing sealant where the pumps and hull meet? This is easier to determine when you have one good engine/pump to compare the bad one too.
Are you sure there is nothing wrapped around the shaft. All it takes is a piece of fishing line or a small twig to cause cavitation.

 

[Scottintexas]

did you take a test ride before you bought it ?

Since you did have a time it did run fine, did you nurse it past the 3400k range or just hit the throttles forward,

I had cavitation once because of loose/missing silicone in the intake housing, sometime I could nurse it past the forbidden zone to get full power,

It would be rare that intermediate bearing/seal is causing cavitation, we just don't see that, even when they leak members don't complain of cavitation that I recall,

I might tell you to pull the impeller shaft to get a better view and make sure your silicone looks good, look from under the boat up into the intake grate area as well as from behind, we had somebody a month ago that had checked their pump/shaft well but then found debris when they pulled the shaft,

I also wonder since it's a '16 if maybe your not getting limited by the ecu for some other reason?

or if maybe your plugs weren't in good, I know you said you checked them but maybe after a week in the water they swelled up and then when you stopped they loosened back up,

where are you at?

 

[swatski]

If they sucked a rope they could have damaged the tunnel but hat would be one side cavitating/acting up...

And this is the part that I find confusing

Trip #2; *boat had sat in water at the dock for 1 full week. I got back in, and sped down the lake, NO ISSUES. Stopped for a minute, turned the auto bilge on, spun around; 7mph MAX again. 3,4000 MAX rpm.

Almost sounds like the engines going into the limp mode, are you throwing any codes?

--

 

[Scottintexas]

yes, I forgot to ask is this only one motor or are both having issues?