tim,i feel bad for you.i really can,t tell from the pictures but do i see tuliping on some of the valves?on a side note about 10 years ago i bought an edelbrock kit for one of my harleys,it consisted of pistons pins&clips rings cams and cnc heads.it ran for 2 minutes and stuck a valve.when i called edelbrock to tell them about the failure i mentioned that i suspected a tight stem to guide clearance,the guy told me that it was not possible and they had me send the head to them for checking.long story short,they sent me a new head with gaskets but never called me back to tell me their findings.it just so happens that the guy who owns the business i purchased the kit from is a personal friend of vic edelbrock so he made a call and got vic involved.the failure was caused from the person who assembled the head forgot to lube the stem prior to instalation.i am in no way saying that is your issue but it is a posibility.do you see any signs of galling in the guide or on the stem?

Valves not tulips that's how they were new..

I am texting you a video tell me thought...

Yes

I am not blaming any one person at this time, when I have guides checked and see why lifter is stuck from coming out of the bore I will see what happened...

There are a few things that can cause this so more research needs done, I certainly expected no issues

Man I`m feeling your pain Tim, sorry to hear about your troubles that really sucks buddy.:(

Wow. Heartbreaker. My condolences.

What about galling on valve and guide whether cause by heat, tolerance or lack of oil.

How about the cylinder wall and piston........any galling there?

I bet the circulating pump impeller failed....causing a hot spot around number 7 cylinder.

Why does it always have to be number 7 cylinder when number 8 is farther away from the coolant sourse ?

It was #2. On a big block Chevy, the fuel pump is located on the even bank side, in the front of the block. Like in the picture shows. #7 is in the rear, on the opposite side.

Then 4-2 fire next to each other...

Honestly I give, I don't care, I don't wanna care, I don't think I am gonna move forward, might sell the good engine, sell parts off the bad one, take a loss and move on.... stock 420's will have to work, buy 500 hour ones that will run another few hundred hours.... this tapped me, hurt me and is turning me off to having cool boat... f this crap. this should not have hapened no matter what, yes I get that it does, and will but happens to me too often, f this