Impeller Vibration

[IDoSeaDoo]

Ok, I got one for you guys. 2004 Seadoo GTX drivetrain in a 1997 Seadoo Challenger boat. I built this boat a while back and just used all the GTX parts initially. The prop was the regular non-swirl 4 blade one with 11/19 pitch. I ate some rocks and decided to try the swirl prop from an 05 GTX. I bought a used one off eBay. It looked completely perfect when it arrived. I installed it into my newly rebuilt pump with a stainless wear ring and went riding. I did notice a slight vibration at high rpm, but didn't think much of it. Later that day my engine started making a horrible sound. I got towed back and found that my thrust washer was completely destroyed and my crank was walking. WOW. I had also noticed that my motor mounts were worn out and one or two were actually broken. I thought that was my issue, so I replaced the mounts and the thrust washer, reassembled and went out on it again. Again I noticed a slight vibration at high RPM and not 8 engine hours later, the exact same thing happened.

This time, I suspected the prop. I sent it off to Impros, where Glen balanced and made it perfect again. I installed it and AGAIN felt those vibrations. The motor revved up fine with very little cavitation up to 7600, but as soon as I felt those vibes, I eased back down and idled back to the dock and installed my old impeller. I sent it back to Glen, who confirmed that the prop was perfect, but he sent me another one just like it, also in mint condition. I installed it and IT TOO had that same vibration at WOT.

So why would it be doing this? Is this related to pitch? This is a very similar drivetrain to the larger 4tec boats that use the 150hp n/a motors. Same motor, same pump and driveshaft. Does anyone know what pitch they run? Anyone have any clue as to why I'm getting these vibrations? I'm deathly afraid to blow up another thrust washer but would love a better prop that doesn't cavitate so much. The stock one doesn't hook up right away when you punch it from idle and loses too much RPM on hard turns.

 

[POPPS]

Check that you did not mash your internal pump bearings,,,there are 2 of them in the housing,,,check that the thrust bearing is not mashed,,,check that the pump seal is there,,,sometimes people omit them,,,i think yours is the neoprene one,,,if that is mashed or missing it will vibrate like hell from personal experience,,,and lastly, before you remove the pump, start the boat,,,and go under the intake grate and see if your drive shaft is wobbly,,bent,,,unlikely here,,,but easy to remove from your equations.
Also,,,putting in a pwc prop into a jet boat,,,may not work,,,the engineers carefully calculate their pitches so that boat/ski,,,can get out of the hole from a standstill, and also have top end,,your ski prop may not propel a large heavy jet boat and just cavitate,

 

[IDoSeaDoo]

Well, when I go back to the original prop, everything is smooth again at all rpm. But I have more cavitation and less thrust. I would think the impellers are the same width because literally everything is the same between 2003 and 2005 in terms of dimensions. Nothing is being mashed and the pump bearings are new. The seal is present.

 

[POPPS]

The space between the prop and the wear ring should not exceed 1mm.

 

[IDoSeaDoo]

Stainless wear ring and brand new prop. You could hardly slide a sheet of paper in there

 

[IDoSeaDoo]

Here is one thing I forgot to mention: I did bore the venturi and steering nozzle by about 3mm, so they let more water out now. It has reduced my top speed by about 5mph. I wanted the top speed lower while gaining holeshot.