I ran my superboat last week for about 2 hours. Came home flushed it out and the motor started knocking after about 2 minutes on the hose. Removed oil filter,cut open and found nothing. Fast forward to today. New filter,ran on hose for about 30 minutes 155-160 degrees no knock.Oil pressure 40-45 at idle. Its a 502 efi aluminum heads Imco exhaust with Eddie Marine slip in mufflers. Any thoughts? Thanks

Just by chance.... did you have the drive trimmed up when you heard the knock?

Yes I did.

If you run the engine with the drive trimmed up, the u-joints can knock due to the increased angle and stress they are under.

X2. And yes, they will make a hell of a racket - especially if they're getting worn. Try running the boat off the hose again starting with the drive down. Then raise it up slowly to see if you replicate the sound.

Ok so the u-joints turn even in neutral ? Just curious,how fast are they turning. I forgot to mention that its a Bravo one drive if that matters

They are turning at the same speed as the engine.

Ok,thanks for the info guys. Learn something new everyday.

Start it and turn the wheel hard over side to side. If it knocks when it is hard over most likely u-joints but could be a dry gimbal bearing too . If it knocks pump some grease into the gimbal bearing Zert and restatrt and repeat side to side motion . If you still hear the noise it is time for new universals.

Dry Gimbal bearings make a hell of a racket on the hose in the driveway that most likely you would not hear over the exhaust while out on the water.

The shift cable is actually switching inside the drive. You will have to disconnect when/if you pull drive. I would suggest pulling it to grease u joint and feel gimbal bearing. Cheap insurance. "Youtube" is your friend. I have done more work than I could have by reading these forums and watching videos!!