HP500 carnage

[insanity]

Had some motor issues that came to light last weekend on a family members boat. Went to change the oil in the port motor and it was about 2 quarts high and a little milky. After a leakdown test found a blown head gasket in the number 7 cylinder. My question is how long would water have to sit in a cylinder to cause this amount of rust? I'm thinking it sat like this all winter and now most likely the rings are stuck. Problem came to light last weekend on the way home from LSC. From the looks of the rest of the motor it has been wet for awhile, both motors have been running cool, but the only time we had a good run last year was october and a few times this year. I just figured they were running cool because of the cold water but after opening things up, these things are starting to look like they need some serious attention. We'll be pulling this motor out of the boat this weekend to have a pro go through it, will be doing compression/leakdown test on the other motor once this one is out and all the open fuel lines have been sealed off.











Port head:


Stbd head:


Lifter valley pan:

 

[Chris]

The cylinder bore looks fresh to me. If it were over the winter you wouldn't be seeing any bare steel

 

[Trim'd Up]

I don't think it has been leaking for long, definately not over the winter.

 

[insanity]

Supposedly the motor was rebuilt around 140 hours ago. The rust scale in the cylinder is pretty rough, about like a piece of 120 grit sand paper, last time we ran the boat was last weekend. I pressure tested the cooling system around Wednesday and that's when we found water getting into the cylinder, but we drained the cylinder with a vacuum and sprayed wd-40 in it. I wouldn't think the scale would build up that quickly in just two or three days???

And I'm guessing the motor needs to come out and be at the minimum honed to clean up the rust scale?

 

[Geronimo36]

springs are rusted, they should be replaced. rust causes stress risers which cause them to break.

If the rings aren't seized into the piston you can probably get away with springs, surfacing and quick touching on the valves.

Otherwise you'll need to re-ring the pistons and check the bearings.... If you haven't done it already, pour a bunch of ATF or CRC in all the cylinders to prevent the rings from sticking inside the pistions. WD-40 isn't good enough. Now that you have it open the air has gotten to it and the decline of the engine has begun.. get on it quick!