I'm a West Coast, Lake Meade, Lake Mohave, fresh water only, family Power boater, 2003 Model, Deep V, 25' Advantage with a 496HO/Bravo IO, 463 hours on it now with a blown connecting rod on # 6 cylinder.
I never had a problem with anything, until 425 hours, when I had the wrong repair shop replace an impeller without back flushing ALL the old impeller out. To correct that issue, because #5 & 7 cylinders overheated and the computer shut the engine down, the result was to rebuild the engine, by my regular repair/service guy who used an engine rebuilder he has used for 17 years. After major dollars, I got back in the water, in May, being gentle to break the new engine in, according to instructions from my "good guy repair shop" and returning it to him for "After rebuild break in oil change and service", at 442 hours.
Last Wed., after running a while and stopping to drift, I started the engine and I noticed a small amount of white smoke coming out of the exhaust. After watching it 15 se4conds or so, it seemed to disappear so I dismissed it. The next day out while running 40 to 45 MPH, for a trip across the basin for 15 miles, never missing and sounding great, I heard what sounded like the transom was coming off! The result was/is number 6 cylinder connecting rod broke at 463 hrs, 38 hrs after rebuilding the engine by a guy I do not know!
Here's the reason for my post: I'm looking for an answer from experienced boat owners/builders/mechanics to tell me what the smoke was and could it have been some part of why the rod broke? Another question is WHO IS RESPONSIBLE TO PAY FOR IT TO BE FIXED?

the white smoke is the oil getting pass the rings into the firing chamber.. although would bad rings cause a rod to fire off. i cannot tell you. its a possibility.

Do you know where the rod "broke"

your going to try and get him to pay but in the end your going to pay. Your going to say phuck it and just buy a blue motor.

When you had the motor done and paid your hard earned cash to the "engine builder" what did the written contract/warranty say?

The person you had the contract with is who you need to deal with. If he used a sub for the engine rebuild, then that is between them.

Did they give you a warranty?????

If you plan on going boating anytime soon you are gonna buck up and pay to get it fixed.

Then, depending on the situation, the person that you you contracted to do the work will either make it right or they won't. Also, keep in mind if it is a twin engine boat you should probably pro-actively pull the other motor apart because if they messed up one they probably messed up both of them.

If they don't make it right in your eyes then you can at least file suit against them so there is public record of your experiences. Depending on where the shop is located and how much business they do you can let everyone know your experience so other customers don't make the same mistake. If they were smart they would try to make it right with you rather than cost themselves 10's or even 100's of thousands of dollars in lost revenue.

Good luck!!

...diagnose your failure with no parts or pictures in hand.

Having not seen it and by your description, the white smoke sounds more like water vapor to me.

Making the assumption that since it was a fresh rebuild you were keeping your eye on the oil pressure and further more, the pressure was good, you need to look at these first thoughts.

It would be handy to know where the rod broke. If it broke at the wrist or journal; could be faulty installation or defective part. If it broke (more or less) in the middle; could be the cylinder hydroed or defective part. I'm leaning to a hydro.

Just a seat of the pants, wild hair, stab in the dark thought. When the engine comes apart pay special attention to the intake manifold gasket.

If that is fine, then pay that same attention to the head gasket.

Also, take great care to examine the exhaust manifolds.

If it did hydro, that usually comes from the exhaust side, but you were running and then it started, so I am (and reserve the right to change my mind) leaning to the intake side.

When it comes apart it will be interesting to hear what you found.

Curious as to if the engine was bone stock? Such as no aftermarket anything including exhaust..

+1, Did they pressure test the exhaust manifolds? Sounds like that could of caused your initial and second failure. The engine builder may not of ever seen the exhaust manifolds.

Welcome to the Wonderful World of Boating ....