96 GTX 787 - Bad cavitation

[eavega]

Okay, so I did a top end rebuild on my 96 GTX after a piston shattered. Prior to the piston shattering, it was running fine (at least for a day). Anyway, fast forward to today, put the ski in the water for the first time, started up, idles fine, revs to about 4500 RPM, and then the impeller breaks loose. I checked the wear ring and impeller. The wear ring is very tight, no light between the impeller and the ring. Impeller is also in great shape, no dings, gouges or deformities. at 4500 RPM I am not on plane, but rather plowing through the water. Once or twice I was able to baby the throttle to get up on plane, and once that happened I was able to move through the entire throttle range (I was breaking in the top end, so I tried not to go full throttle at any extended amount of time).

The last thing I noticed was an large amount of water in the hull at the end of the day, I'd estimate a full 4 inches of water in the hull. In my haste to beat a storm I didn't get a chance to run the ski with the seat off to see if water was leaking anywhere.

I don't know a ton about PWCs, this is the second one I have brought back and by far the most complicated one. My initial thoughts on this based on other things I've read is that the carbon seal could have possibly gone bad, which allows air into the jet pump and causes the cavitation. I never removed the pump when I pulled the engine, so getting the engine back in required a fair bit of jostling the shaft that goes into the PTO flywheel. Could I have damaged the carbon seal with all that moving back and forth? Should I be looking elsewhere for the cause of my cavitation? any thoughts or observations would be greatly appreciated. I've got the motor running well, and I would really like to be able to use this ski this summer!

Rgds

Eric

 

[jjsinaz]

Cavitation along with water in the hull would point toward the carbon seal being bad. Good first place to start. Also, did you properly align the engine after having it out. since you say you did not remove the pump I suspect not. That could be the cause of the carbon seal not doing it's job.

 

[eavega]

Okay, guilty as charged, I thought that by not removing the pump, the engine would correctly align as long as I used the same shims in the same place. So, what's the right move here? Pull the pump check alignment? Will the carbon seal still need to be replaced? I am ready to atone for my sins.

-Eric

 

[jjsinaz]

You would think that if you put the shims back the same way they were, unless it was out of alignment before you started, that it would line back up the same way. The consensus on the forum seems to be that if you remove the engine, you need to re align it with the tool. Maybe someone else will chime in with another opinion. I would like to remove the engine from mine at some point to repaint it and clean the hull up a little better, but I haven't done so because I didn't want to have to get a tool to re align the engine. As for the seal I would inspect the face of the carbon ring and the mating surface of the top hat flange on the driveshaft and of they are not gouged up or worn unevenly it should be okay.

 

[soccerdad]

Sounds like your carbon seal is leaking badly for that much water to be coming in. You should be able to see it if you run it in water with the seat off. You can sometimes make it better by pumping in a little grease into the PTO zerk fitting. This pushes the drive shaft back and tightens up the CS. You can also use zip ties to sqeeze the flexible hose that holds the CS and that will push it forward some. Search around and you will find a bunch on alignment and alignment tools. I built one cheap, but some do not like the design. Worked for me though.

 

[eavega]

Okay, so I took a good look at it today. Removed the plastic cover and what did I find? The clamp had come off on the cs side of the accordion boot. I'm wondering if that was enough to cause the cavitation? I want to run it out to the lake to see if that was it.
I have a local shop that quoted me basically one hour of labor to check alignment and fix it if it's off, and since I need to remove the pump I'm going to change the wear ring, new Solas impeller, and replace the whole carbon ring assembly, but I want to know if I have conquered the cavitation problem before all that gets done.

 

[wfo speedracer]

Okay, so I took a good look at it today. Removed the plastic cover and what did I find? The clamp had come off on the cs side of the accordion boot. I'm wondering if that was enough to cause the cavitation? I want to run it out to the lake to see if that was it.
I have a local shop that quoted me basically one hour of labor to check alignment and fix it if it's off, and since I need to remove the pump I'm going to change the wear ring, new Solas impeller, and replace the whole carbon ring assembly, but I want to know if I have conquered the cavitation problem before all that gets done.

Yes a loose or broken clamp will cause excessive cavitation.

 

[eavega]

Welp, I replaced the clamp, took the ski out to the lake, and it ran great, for about 2 minutes, then it started cavitating again. This time I took it to the shallows and pulled the seat. The carbon seal/boot was spraying water and shaking like crazy. I noticed the clamp was gone again. Shut down, and found the clamp in the hull. It didn't just slip off, it actually snapped! I got home and pulled the pump (needed to do that anyway to get the motor aligned, and to replace the carbon ring) and here is what I found

That would be a driveshaft with a bend in it! apart from that, the carbon ring was trashed. Probably needed to have had the engine aligned before I decided to run it. Luckily the splines in the PTO flywheel are still good, I don't think I did any other damage to the ski.

We never learn a lesson so well as a lesson learned from a mistake. New driveshaft is on order, ski will be at the shop getting engine aligned tomorrow. Hopefully back on the water by weekend after next.

Follow up question for anyone who has read this far, I ordered a driveshaft seal kit so that I can replace all the components. When I pulled the one off of the existing drive shaft, it has an o-ring to keep the metal ring in place. The kit comes with a metal half-moon ring. Does the ring just sit in the groove previously occupied by the o-ring? That is what I am seeing on the youtube videos showing replacement of the carbon ring assembly, but I wanted to be sure I didn't need a different drive shaft, or need the o-ring that was there previously. Thanks in advance for any information.

Rgds

-Eric

 

[soccerdad]

Well that will do it! I didn't know that a misaligned motor could do that. Still not sure how, but anyway, that is your cavitation problem. Yes, the metal clip just replaces the o-ring. It was an update as the o-rings could fail sometimes (and cause cavitation or a sinking ski...)