Loud rattle/banging noise

[the454assassian]

I am helping out my cousin with his boat. He let a friend store it over the winter as long as he could use it from time to time. Needless to say the boat was not returned in the same condition. Blown fuse on starter, tripped breaker on motor, fuel issue either water or trash in it prop slipping and loud noise. I have every thing fixed but the noise and fuel issue. Its an 07 caravelle 18ft with a 4.3 mercruiser. When you fire the motor up it sounds good at idle. But when you rev it up look out haha. around 1500 rpms you can start to hear a rattling noise. When the throttle increases above that the noise gets louder (metallic sound). If it gets above 2300rpms the noise is louder than the engine and you can feel it. I am an auto mechanic and my instinct when I hear a noise that loud and strong is to shut down the engine to prevent damage. I used a stethoscope and the loudest places I hear the noise at 1500 rpms is at the bottom of the y pipe and on the back of the motor on a bolt that looks like motor mount bolt/stud behind the distributor right above the flywheel. I am not familiar with this noise but it very strong. Anyone got any ideas of where we should look or start?

 

[Alumarine]

It could be the ujoints in the drive?

 

[the454assassian]

It does it in gear and in neutral

 

[Scott Danforth]

U-joints spin when ever the motor is running. Alpha drives shift by dog clutches in the lower unit

 

[Bt Doctur]

start by pulling the outdrive

 

[the454assassian]

So the out drive got pulled today. and guess what I saw before the shaft was all the way out. A ball bearing sitting in oil and water mixture in the bellows. So the gimbal bearing failed. I am surprised that more damage wasn't done. I can see several pieces of the bearing inside there. So does anyone know of a kit that includes the bearing and u joints?

 

[Bt Doctur]

not as a kit , available seperately