4.3 mercruiser vibration

[Susquehanna Squid]

So I had my 4.3 L merc 2012 Glastron out on the water today. I was moving along just fine at about 3200 rpm’s and all of a sudden it felt like I hit bottom. There was a loud bang and a terrible vibration. However, I did not hit bottom. There was not a mark on the outdrive or propeller. Now, if I go any faster than idle the boat shakes violently. Any ideas? Thank you in advance for any help!

 

[QBhoy]

If you’re sure you didn’t hit the bottom it can only be a few things.
My guesses
the hub in prop may be damaged from before
the prop has damage on it and out of balance
the coupler is worn at the splines
you have gearbox damage

will be a few other reasons but likely it’s something rotational that’s damaged

 

[alldodge]

Agree, need to pull the drive

 

[Susquehanna Squid]

I assumed as much. I am dragging it to the dealership today. Thanks for the info gentlemen!

 

[Lowlysubaruguy]

Does it vibrate in neutral at the same RPMs and its a vibration not an engine miss?
The Ujoints are spinning any time the engine is running. If its still there in neutral it could be a U joint and that should rule out the prop and most of the drive? Is the noise still there you might get an idea with a stethoscope as to where the issue lies. You'd be best having someone replace the U joints but pulling the drive is pretty basic mechanical work. If its to not there in Neutral something else like mentioned the props having an issue simple enough to pull the prop and see if its gone. If its still there with the prop off and not in neutral then its most likely in the drive.