Bayliner Jazz -Cavitation or shaft damage?

[RogerB]

'94 Jazz, 90HP. Hit the throttle a little and it is either cavitating or something is terribly wrong with the impeller shaft. No obstructions, and the ride plate seal looks good. Wear ring/impeller clearance looks like .020. Happened all at once, so that leads me to believe it might be the shaft. Anybody had one apart? Any similar problem? I have completely rebuilt the engine, and it runs great, other than this.

 

[kenimpzoom]

Re: Bayliner Jazz -Cavitation or shaft damage?

Roger, is this a 90 hp Mercury Sport Jet?<br /><br />Are you suggesting the impeller has spun on the shaft?<br /><br />Have you checked the pinion?<br /><br />Ken

 

[funpilot]

Re: Bayliner Jazz -Cavitation or shaft damage?

How is your acceleration, despite the vibration? Look between the impeller blades, they overlap so much that if a bit of log or a rock is jammed in there, you could miss it and the boat will do exactly what you are susggesting. It is a pretty solid unit, but vibrations can travel from the powerhead/jetpump to the hull pretty easily. Check the flywheel guard if you have one, and any other item on the motor to see if it is loose and creating a ruckus.<br /><br />good luck<br />fp

 

[RogerB]

Re: Bayliner Jazz -Cavitation or shaft damage?

Thanks for the replies. I had the boat out again today. Same problem. If the pinion was shot, I can't believe the boat would go at all. No grinding sounds. Can exaust get into the jet stream? Can the ride plate seal let air get to the impeller? Give the boat any gas at all to get it up on plane, and the engine just revs higher. The boat just doesn't go any faster. Two of us checked for debris in the impeller, both from the back and the bottom. That was our first thought also. I will keep looking and write a reply if I find out what is wrong.

 

[RogerB]

Re: Bayliner Jazz -Cavitation or shaft damage?

The problem is solved! No money involved! I was underneath looking for something lodged in the impeller. I noticed a loose screw at the back of the ride plate. All of them were loose! I tightened them up and went for a ride...a great ride! Back to normal. I learned a valuable lesson. Hope this helps someone else. RogerB