Is there any history or tell tale signs of overheating at one time? If the paint is crispy around the manifolds it might have gotten hot & cracked a manifold. How straight are the pipes coming out of the risers? Just trying to think the problem. Randy

I would spin it without the plugs, put the plugs back in it and fire it . The chances of bending a rod using the starter are slim ( you said you didn't think it fired).Bring it up to temp, shut it off and pull plugs. Let it sit overnight and spin it with the plugs out, look for water coming out of a cylinder. But that is just me.....

This happened to me last year. We were trailering the boat when it must've happened. The boat sat two weeks before we discovered the problem. As we tested the boat at home on the hose it would not turn over and made a sickening thunk.

I pulled the plugs and then manually turned the engine, flushing out a lot of water from one of the cylinders. Then it would spin freely with the starter. I changed the oil, oil filter and spark plugs. After that it ran fine and continues perfectly to this day.

I am not sure how the water got in but I figured that as we were shutting down the motor with the corsa exhaust on, a wave must've hit the back of the boat as it was getting onto the trailer.

Back to the flappers. Do you have internal and external flappers. You need both. Lift up the external flappers and shine a light up in the pipes. You should have internals also. If theyare gone it will just happen again if not replaced. Check your other engine also.

no internal flappers maybe turn the silent choice switch on. this would close the gap while sitting.

this is an ex salt water boat. I have seen numerous posts of these aluminum 496 manifolds rotted and leaking. I have to tell you I am scared to put this manifold back on. if it leaks that engine is done.

hmmmmmm......interesting. exactly what I had.

no over heating. the pipes have good angle on the trailer and even more in the water.

'05 might be cast iron instead of aluminum. All had stainless risers. Put a magnet to the manifold and see which you have.

what ever you do,,replace the exhaust tips with ones that have internal flappers...