If memory serves me -- didn't the Stihl boat have a drive fly off and some enormous speed -- I saw the video and it was a wild ride until they got it slowed way down. Glad no injury to you

3pointstar

Wil have to do a search on that one. But ya with twins it's not what I'd call a good time. I couldn't imagine at speeds now a days.

Thanks guys, I'll try to get with him and try swapping the drives. Good idea on the insurance, it probably will cover the cost of fixing it, minus deductible of course.

A little late on results, but we put the Bravo1 drive on and it still has the noise, but not as loud maybe.
Then after some soul searching (Vacation to Lake Powell) we pulled the motor and don't see anything wrong with anything, like the coupler or flywheel. Then we pulled the valve covers to check for any broken rocker arms or anything bent: nothing. Then we pulled the pan and checked the main bearings and found nothing bad, or anything in the oil. Motor runs perfect by the way.
We are at a lose as to what is making this noise.
Unless someone has any grand ideas, I guess we'll put it back together and see if the noise is gone.

Probably a wrist pin. just put an engine in my mother's boat for the exact same noise. 2001 350 carb engine. It wouldn't make a sound until 2500 rpm under a load. Tore engine down and the pins and pin bores were worn. Everything else looked perfect.

A blown head gasket will make one hell of a racket above 2500 rpm under load, did you check compression?

Did you check the gimbal bearing, or replace it?

sometimes you won't hear an engine knock at no load.

Funny, we were talking about that as a possibility this morning before I checked my email. Knowing it has over 500 hours, I think I have him convinced to go through the motor so he doesn't have any problems with it next summer. Hopefully we can find the cause of the noise. I'll let you know what he decides to do, but if it were me I would rebuild it, now that it's out of the boat.
Thanks to everyone for the ideas!

I just bought one from jasper Engines for around 2K. I don't think that I could rebuild one for that