Mercruiser 8.1s 496 Hydro locked

[Searay45]

I have an 07 Sea Ray Sedan Bridge 36. Two weeks, I came into the dock after a nice run. Shut the engines off and waited for some friends maybe an hour or two. Went to restart the boat and port engine fired right up, starboard turned a small amount and then clicked. I pulled the plugs and water came out of the number 3 cylinder. I check the oil looked perfect. I pulled the rest of the plugs no sign of water. I turned the engine over with no plugs and coated the inside with fogging oil. This week came down and installed new risers, manifolds, plugs and wires. It fired right up but had a loud knock. I very carefully raised the rpms up to 2,000 the knock went away but you could still feel a vibration and a cylinder not firing (guessing). I quickly took it back to idle and the knock became much louder.

Question is, I know a bent rod is probably what happen but I never had the engine lock up when running. Anything else you have seen cause a loud knock on a 496?

 

[paulswagelock]

My guess is the attempted start did the damage. All guesses until you do a tear down. Bummer.

 

[scoflaw]

That rotating assembly is all cast parts which means it's not that strong. Don't sound good but best of luck

Run it with that #3 plug out see if the knock goes away

 

[Searay45]

Update... Rookie mistake but man am I glad it was just my mistake. This week I went down and decided to pull the wire off the coil and see if the sound changes. Nothing changed but when I looked at the plug wires I noticed I had the two cylinders swapped. I swapped them back and boom knock went away. Man, did I get lucky!!!

Took the boat out for a run. It ran great as soon as I went above 3,700rpm. Both engines shut off with a loud beep. I checked my smart craft and it was MAP Sensor Hi fault "Port". Which is the other engine from the one that was hydro locked. Any thoughts? I did not dive into it as I ran out of time this weekend. I just got home and ordered another MAP sensor but also curious about what else it could be......Any Thoughts?

 

[CaptRonn]

Update... Rookie mistake but man am I glad it was just my mistake. This week I went down and decided to pull the wire off the coil and see if the sound changes. Nothing changed but when I looked at the plug wires I noticed I had the two cylinders swapped. I swapped them back and boom knock went away. Man, did I get lucky!!!

Took the boat out for a run. It ran great as soon as I went above 3,700rpm. Both engines shut off with a loud beep. I checked my smart craft and it was MAP Sensor Hi fault "Port". Which is the other engine from the one that was hydro locked. Any thoughts? I did not dive into it as I ran out of time this weekend. I just got home and ordered another MAP sensor but also curious about what else it could be......Any Thoughts?

Curious. How many years/hours did you have on your old manifolds?

 

[Searay45]

Curious. How many years/hours did you have on your old manifolds?

I have a receipt of the risers and manifolds being replaced in 2016 at 485 hours(before I owned the boat). The boat had 557 hours when I purchased (Dec 2017) it now has 785 hours. The risers looked ok but the manifolds were horrible.

 

[CaptRonn]

I have a receipt of the risers and manifolds being replaced in 2016 at 485 hours(before I owned the boat). The boat had 557 hours when I purchased (Dec 2017) it now has 785 hours. The risers looked ok but the manifolds were horrible.

Interesting. Were they OEM (Mercruiser) manifolds?

 

[Searay45]

Interesting. Were they OEM (Mercruiser) manifolds?

Yes, they were OEM but the boat was on the gulf side of Florida and sat in the water all year. I believe the salt content in the gulf is very high as well. I will make sure to spray the outside with an anti corrison spray and keep an eye on them now. Too expensive to replace every 4 years

 

[CaptRonn]

Yes, they were OEM but the boat was on the gulf side of Florida and sat in the water all year. I believe the salt content in the gulf is very high as well. I will make sure to spray the outside with an anti corrison spray and keep an eye on them now. Too expensive to replace every 4 years

Thanks for the update. So when you said the manifolds were "horrible" was that in reference to the exterior or interior?

You may wish to set up a system that you can rinse out your manifolds with salt away or another method after you run the boat. Supposedly the new style OEM manifolds have a better "E" coating to extend life.

Thanks for the details on your manifolds.

 

[Searay45]

Thanks for the update. So when you said the manifolds were "horrible" was that in reference to the exterior or interior?

You may wish to set up a system that you can rinse out your manifolds with salt away or another method after you run the boat. Supposedly the new style OEM manifolds have a better "E" coating to extend life.

Thanks for the details on your manifolds.

The boat is now in freshwater so I should not run into that issue.

The inside of the risers were just as bad as the outside.