Bent rod, u joints, or ?
 

Throwing this out there to get other options. I have a friend that has a boat with 6.2 engine. He said he was running around 45 mph when the motor starting make a loud noise. When engine in in neutral there is no noise at all. When you rev up engine no noise either. In gear, still no noise. Noise starts when reving engine up around 1300 rpm. I though it was the u joints when I heard it. He has his engine people come out and they thought it was in the outdrive. They took boat to shop and pulled outdrive. Pulled covers and drained oil and said drive was OK. They then put outdrive back on and put boat in test tank. The boat shop then told him motor had a bend rod and was needing to redue the motor. I have never heard a motor that did not make noise with no load that had a bent rod, so I am thinking problem is not a bent rod.

What are your thoughts?

i doubt it is a bent rod,time for a second opinion from a different shop.

There is no way they can tell if its a bent rod until they take it apart. It could be a number of things. I would say a bent rod is highly unlikely.

I had an engine in car start knocking. I would have sworn it was rod bearing from the knocking sound. It was a bad wristpin.

It may not be a broken rod, when we had broken rods on the 540 and started it up it didnt start. You need to take the engine apart to figure out what it is

Thanks for the input. I was starting to second guess myself. I feel problem is in outdrive or u joints since it would not make any noise when either idle in or out of gear or when in neutral and motor reved up.

borrow another drive if possible. could also be problem with coupler. i bent a rod hydrolocking a small block. piston hit crank throw every rotation. could hear it while cranking on starter.

Simple test. pull the outdrive, remove the seawater hose at the transom assembly and stick the garden hose in it so the motor has water, start it up and rev it. if no noise its the drive, if noise time to pull the motor.