maybe this will help, flow the oil against the water

I have just looked over this thread, with the pictures a couple of times....I must say; from your quoted words; You admit you had seaweed packed inside the water intake the size of a baseball...are you running as single large pick-up, feeding both engines or two separate pick-ups, with two sea strainers.......?
You say water temp was 140- 150.... was that ambient temp or actual water temp, if no water was flowing....you will be reading ambient temp..

These pistons are showing scuffing only on the thrust side, if cleanance was a issue that would show on both sides.... I have never seen, heat transfer or actual burnet oil on the inside of a piston skirt, only combustion gases in a aged engine with poor ring seal.

If you take away water flow, you'll definitely discolor headers.... The water in the block will remain there, doing nothing except increasing in temp, creating steam. NO heat transfer from cylinder walls, oil literally burning on cylinder walls and no lubrication.....Its kind of like having a steam pocket in a closed cooling system, the water maybe 200 plus degrees, but the thermostat won't open because the water isn't actually touching the thermostat only ambient air....same goes for temp sender in that general area.

Question; Is your engine warning system operational ? low oil pressure and high water temperature ? After 10 hrs of running and this happens, it's not from clearance issues... Did you dyno this engine ??? If clearance was a issue, this would have been done on the dyno... The rocker arm being loose off center, if you expand alum enough, things can loosen up, aluminum expands at a faster rate than the steel bolts that hold the rocker arm stands down. I have used plenty of the Jesel sportsman Sets, that's a good stand for the money... It not rated for a Spring of 385 seat and 800 open....

Being the sea strainer was blocked/ restricted, headers turning color........ Saying, NO SCREEN IN STRAINER, why is there no screen ?????

I would like to know more about the water pickup system.... What is the condition of the other engine if so ?

There is one large pickup which divides into 2 halves internally. Those two halves have individual hoses and shutoff valves which feed strainers. The strainers have screens. The intake on the outside of the boat does not have any screen so it can suck up anything that fits in. I have to assume the 140-150 is the actual water temp as that is what it has read every time the boat has been run once it warms up. The engines have high water temp alarms and low oil pressure alarms. The rocker arms that were out of position were still tight on disassembly

When my first rebuild went bad after 10 hrs of run time my pistons looked EXACTLY like this. One was so bad the cyl had to be sleeved. I always had 50 lbs of oil pressure and ZERO heat issues(cross overs no thermostat) oil temp was still 220. Took it apart had Ben at Precision Power Offshore rebuild them. Put it on the dyno and found the jetting to be lean as hell under load at 3000 to 4000 but great at WFO.

BCK I feel for ya I can't help on the look of the bearings or the rockers not being straight on the valve but it sure looks like terrible detonation by the looks of the pistons. think I still have that piston somewhere

So you are telling the engine didn't overheat, even with the seaweed clogged in inlet?

horsepower1 (Scott) Please remove your "Like" from my "Post"

The only gauge that moved was the oil temp on 1 engine, which is why I have doubts as to how hot the engines got. When I stopped the boat to determine why I discovered the clogged strainers. Both engines were already knocking at this point. After pulling boat I discovered intake on transom also clogged up. The only physical evidence of overheating is 1 discolored header and whatever the pics in this thread show. I believe the engines definitely got hot. Trying to determine if they got hot enough to ruin what were otherwise good engines or whether engines were marginal from day one and should have survived this

I'm being told that on the filter housings I have the temp is taken before oil would pass through cooler. If that info is correct then oil temp leaving the engine never exceeded 240

The temp sensors read vapor temps with a very slow response time. So, if you were not getting water flow, they would have been surrounded by steam / air and read incorrectly. It takes a long time for the heat to get high enough to read on a temp sensor that does not have water on it. I burned up a car engine when it dumped the water quickly - temp sensors got into the hot range after it started showing signs of damage. Even after I stopped, it took a long time for them to hit the overheat range on the gauge.

The problem I see is that the build was not all you expected. But, the motors most likely did get hot enough to hurt them if they were knocking and the headers blued, first sign for me of no water is usually a change in exhaust note followed by the smell of burning exhaust rubber, after which you have seconds to shut it down.

It's a tough situation to be in with little recourse except to make sure you get what you pay for this time. I would suggest getting away from the shared pickup, not much point in having two engines when they are both vulnerable to one plastic bag/sea weed

I wish you better luck and hopefully the engine builder will meet you someway with regard to the cost.