Started getting a knock in my Mark IV - 454, which I initially thought was a collapsed lifter. Drained the oil and was all milky... Pulled the motor and found a blown head gasket by #8 ... Dug deeper into the motor and when spun with a breaker bar somewhat quickly can still hear the knocking... When looking into the same #8 piston/rod, the rod/piston wrist pin bushing is shot or worn out... At the bottom of the stroke the rod moves from one side of the wrist pin to the other and looks like it just touches the side of the piston when the crank is spun just a degree or two... Definitely where the knock is coming from in my opinion as the rest of pistons have no movement in that area...

Definitely going to bring the heads in to get checked out... As well as the short block.

Curious what you guys recommend to do that wont absolutely destroy the bank?

• Disassemble and mangaflux block
• Inspect crank, rods, and pistons - If all OK, then reuse?
• New wrist pins and rod bushings?
• New main bearings?
• New set of rings?
• Inspect cam & reuse if OK? New lifters either way?

When I bought the boat, the PO said it made about 500HP... Its in a 24' Sunsation Rocket 24x7 and runs 70 all day and has run best of 74 a few times... a few forums members have said they think 500HP is about right for my setup and speed??
Unfortunately the cam and lifters are flat tappet... but dont know if a roller setup is going to be in the budget depending on everything else.
Not sure on the specs of the cam, need to pull it yet
Edelbrock 6155 heads...
Singe plane high rise manifolds
AED carb, not sure of specs
EMI Thunder manifolds

Suggestions!?!?!!?!
TIA - Chris

Let me know if the pics dont work....

What rods do you have? Stock gm rods do not have bushings.

To be completely honest I don't know... This is my first time fooling around in the bottom end. If no bushing what's there? Just the wrist pin through the rod?
There's all kinds play in there with just spinning the crank a touch at the bottom of the stroke

How many hours were on the motor before it went south? If I was going to take a stab at what happened, I would say that the head gasket probably blew and allowed water into the chamber, which doesn't compress, leading to either detonation or hydrolock. This is what likely destroyed the wrist pin. What did the bearings look like?

things you need to do:

Check block / head surfaces for straightness - might have to deck block and resurface heads
Check #8 rod to make sure it's not bent
Probably looking at a new set of pistons
Check block / heads for cracks
I would try to save up a little extra money and go with a mild hyd roller cam setup. Too many stories about flat tappets getting wiped to make me comfortable running them.

Also, if you already pulled the lifters and did not keep them paired with the lobes they broke in on, then there is absolutely no way I would try to use that cam again no matter how many hours it has on it.

No clue on hours on the motor BC I bought it already assembled. PO said it was built abt 2 years previous but he had no documentation.

I completely agree on your assessment of what happened.

Didn't look at bearings yet because I want sure if I wanted to completely disassemble or let a machine shop do everything.

Noted on all your recommendations, ill briong that all up with the machine shop... Sux about new pistons but maybe I can match them up with a new roller cam for some power?

I did pull the lifters and keep them all in order with the rest of the valve train fortunately... but if money becomes an issue can I reuse the cam with new flat tappet lifters?

FWIW, I spoke with a buddy today at work that has me mostly convinced to do this all myself minus having everything checked and machined like all BudmaBudman suggestions above but reassemble myself... thoughts?
I am mechanically inclined and can follow instructions and advise very well...

The wrist pin floats in the piston and is pressed into the rod.
Usually it gets loose in the piston and causes noise. Much more likely to egg out the aluminum bore it floats in than to come loose from the small end of the rod.
Budman you know that flat tappet lifters continually rotate in there bore right ? And rollers obviously roll so what does it really matter where they go back?
I'm not a fan of using any valvetrain part over a certain amount of hours anyway just curious your reasoning

I sure wish someone told me to keep the lifters in order a couple hundred jobs ago.

As far as the OPs situation I'm thinking its a bent rod...

the flat tappet cams have some lifters rotating clockwise[50%]the other 50% rotate counterclockwise.this helps control cam endplay.i can,t remember where i read that but i believe it.