nsx, wasn't implying that you didn't know what you were doing on the top end rebuild. I was just commenting on the darkened area between several cylinders that looked in the pictures like a possible blown head gasket. You had mentioned that it had a previous blown head gasket, and you cannot typically deck a block without completely tearing down the bottom end. You mentioned that the block had the proper RA for MLS gaskets - do you have access to an RA tester to verify? Maybe you did. Just tossing some things out there in hopes that you can find the root cause.

You have a good one here . Had a nice piston top color across the board , had that clean spot that kinda said water has been here on that ganked piston . Mls gaskets are majic for 502s but its a ***** getting all that surface area of all that cast iron straight smooth and square. Have never ever seen one fail from being to smooth , if its square. Didnt see that worn nickel from the '70s finish , but im half blind too.
My bet says clogged block passages and or water intrusion on that compromised cyl . Good news is if im right the rods mains ect will be unscathed. But if im wrong ...

Looks like that piston chunk took a little tour around to visit a few other cylinders before the party plug was pulled
I would take a real close look at how the water is flowing around that damaged cylinder. The appearance of cooked graphite could possibly hold another clue

I highly doubt this motor detonated because it didn't have proper RA finish, blown head gasket, water intrusion or whatever. Do you guys have a clue what you are talking about? Every single cylinder shows signs of detonation some more than others.

This guy out there with the hurt 502 is about to find out for himself if he hasnt already .

Just bought this boat natural high
 

Hi , I just bought the boat in this thread. Does anyone know why he changed the 502 out. The boat has a 7.4 l in it now. Does anybody know why he did this. The owner had passed away and I purchased it from his son.

If you are referring about the OP, 92NSX, he is very much alive. He is a part of another forum. Sure he bounces over here once in s while too.

Interesting
 

guess I’m not sure if it’s the same person or not. I saw somewhere else a recent listing of the boat for sale. Said he was for a deceased father. Which the son I purchased it from said his father he recently passed but he said it was his boat. They were from Illinois but the boat is still registered and titled to someone in Minnesota.
Anyways after this supposedly being a great boat with no problems turns out to not be the case. Well I’m ordering parts for a 7.4 l I come to find out on this thread that this boat originally had a 502 efi . Would you happen to know why the motor swap?
also reading past threads I see this boat was supposed to be being parted out due to a cracked hull. Wondering if that’s the reason it’s taking in water at my slip ? Any I do o. This boat is greatly appreciated.

Yep, Rob's a live and well

I did not sell that boat with a 454. I sold it to Chris in 2015 or 16. Had a 502 mpi that had 325-350 hours on it. He was from Illinois but keeping the boat at his cabin in Wisconsin.

I sold it as a parts boat for 6 or 6500( the value of the engine and drive ) . The port side hull was cracked, port side right by the outer chine, cockpit / engine area. I have photos of it some where. Plus more. The back cross member on the trailer that is bent into tuseday.... was from when i dropped a axel at the landing.

So some where down the line he swapped the engine putting in a lower performing engine. The registration and trailer I see is still in my name. So he obviously never switch the titles.....