New YJB owner--Cavitation Problems!

[bandit79]

Howdy from Texas!

I will post in the Welcome section later, but I need to get a direction here.. I've done a lot of searching and reading here. Lots of great info.

I bought a 2006 AR21o last month and have had the boat out 3 times so far. The first time, when launching out of the hole (trying to pull skier/wakeboarder) both engines were hitting the rev limiters, and after some research on here I figured I had cavitation problems. It would take 15 seconds or longer to plane, if at all. Crawled under the boat, checked the grate seals and impellers. Seals seemed fine but starboard side impeller was beat up (see pics) I ordered and replaced the impeller and patched a hole, as whatever the previous owner hit, it poked a hole right next to the drive shaft hole.





On the second trip...The starboard side was working as it should, but the port side was still cavitating on launches. Again, inspecting the grate and impeller, I only found a small forward bend on the impeller but it was at the backside of one of the blades, or not a leading edge. I was thinking maybe the clearance between the edge of the blade and the wear ring was too big and causing problems. So I ordered and replaced port side impeller. Once replaced, took it out for the third time, and it is still having issues on the port engine. Again, trying to launch when pulling a wakeboard, it cavitates. It will also cavitate anytime you try to launch quickly.

A side note here: I did overfill the engines with oil on the first trip. Before the second trip, I removed excess oil and I did have some oil on the starboard air filter. I haven't tried it without the filters yet.

I have removed the port side pump again to have another look. The red arrow is pointing at the offset between the transom plate and shoe?? Of course, it is the opposite on the other side. I searched and I see some guys have smoothed that part out. Also, there is a lack of silicone there as well.




So, would that be enough to cause the cavitation? My only other thought at the moment is that maybe overfilling the oil, somehow has messed up the spark plugs on the port engine?

Your thoughts are appreciated!

--David

 

[itsdgm]

Welcome aboard and sorry to hear about your cavitation issues. Spark plugs and oil will have nothing to do with cavitation. They will only affect max rpms.

Causes for cavitation include:
Out of spec wear ring/impeller gap
Damaged impeller
Leak in the pump which introduces air into pump. Check for missing sealant
Something that disrupts the flow of water into the pump.

Good luck. Hope you figure it out soon

Ps. I couldn't see any of your pics. Might just be me though, I've had spotty Internet.

 

[Murf'n'surf]

I think you've nailed your issue.....sealant is needed in all of those cracks.

What kind of clearance do you have between impeller and housing? Got a pic?

 

[Ronnie]

I'd bet that you are correct in that gap is causing your cavitation issue. My recommendation is to seal it with 3m 4200, smooth it with a razor blade while it is tacky and your cavition issue should be resolved. If you want or test the theory first use rtv silicone instead of 3m 4200 as the former is easier to remove. Don't use 3m 5200. Unfortunately I've learned this the hard way when I succefully adressed a cavitation problem I had in a 230 years ago.

I'm my situation I had gaps and high points seemingly everywhere so I put put new sealant in and smoothed it out along all metal to metal and metal to fiberglass transition points before the impeller even all the way around the impeller housing. I don't thing that little chip at the front of your intake has anything to do with the cavition you are experiencing but it would not be hard at all to patch it so you may as well do so.

Good luck.

 

[Gym]

@bandit79 I think @itsdgm covered all the bases pretty well. Looks like the previous owner may have sucked up a rope. I might add, when you re-silicone you need to dig out the old silicone as new silicone doesn't adhere to old silicone very well. My other concern is the bent blade on your impeller. If you're feeling vibration on the throttle for that side you will not only get cavitation but will cause wear on your bearings. You can send that impeller out to be straightened and dressed or buy a new one.

Whenever you buy a used boat change oil, plugs and grease the main bearings. Also check the air filters as owners and even service people have been known to overfill the oil ruining the filters. Welcome to the club.

 

[buckbuck]

I am not sure what the red stuff is on the bolt holes. If RTV that is ok, but do not use red LocTight on those bolts.

 

[bandit79]

Thanks for the help and great advice. It was exactly what I needed. lol I figured I was headed in the right direction, just needed some affirmation.
Yeah, the starboard side is all patched up and is working great.
The red stuff on the holes wasn't locktite. All bolts came off easily. I bought some blue loctite but haven't put any on.

Fortunately, I didn't have any vibrations on either side. I did go ahead and install two new impellers.

I will grab pic of the clearance between impeller and housing here in a bit.

The plan: I am going to get some 4200, pull the old silicone out, and then put the 4200 in and smooth everything up.