Donman

Was running hard Saturday, after a few minutes of hard running I lost RPM. Could only pull 4800 at WOT (I usually can pull 5800 rpm). I cruise in for lunch, all sounds OK. After an hour, I fire it up and hear a rattle-knock, engine runs rough.
I put it on the trailer and begin diagnosing today.
THE ENGINE: Carbed 454, stroked to 489", Merlin heads, 731 cam, flat-tops, MSD ignition, 800 Holley DP, Carter electric pump. Timing set at 34* total, 140* stat, mix of 89/93 octane fuel.
I didn`t do compression/leakdown test (not sure why I didn`t). First thing I find is fuel psi gauge at carb shows 3 psi with switch on (normally shows 6 psi), bad gauge or ???
I pulled plugs next. #1 has missing center electrode and side electrode is bent sideways... All others look OK. I pulled valve covers, all OK. I pulled intake, looks good.
I figure the worst, so I went ahead and pulled the engine. I look at the bottom end first, all looks good. I pull a few rod caps, everything looking OK. I pull the heads and find "dings" at the top of all pistons (some worse than others), #1 was beat on hard, looks like a screw got loose in each cylinder. The head has same damage.
OK, so I figure I lost fuel pressure and this caused detonation. Is this what detonation looks like?
The knocking / rattle noise concerns me since I haven`t found an obvious reason for it. The cylinder walls look OK, but I haven`t pulled any pistons yet.
Can anyone give me any ideas to look for? Is this detonation? What is causing the knock at idle?
PLEASE HELP ! I want to get back on the water ASAP!

ratman

post clear pics of the pistons

The Menace

Running lean probably caused the electrode to burn off. Then it bounced around from cylinder to cylinder dinging everything in it's path. It is amazing how it can travel through that maze.

If you ever watched "Mythbusters", they dropped a penny down a carb of a running engine. It sounded like a bullet bouncing around inside the motor. The motor kept running for a long time. They poured a lot of other crap into the engine but the penny was not the death blow.

Turbojack

Yep, Detonation.

You may have a bent rod. Since you did not run motor long it might be hard to see what one is bent. Is all of the pistons there? No parts of piston missing? When you pull pistons you may find ring lands broken. Dings in ohter pistons besides one could be as Express said the spark plug center bouncing around or it could just be detonation eating the piston.

A lot of times with detonation the pistons scar up, scuff the sides pretty bad. Might look at how the pistons sides & cylinder walls look like.

Donman

I will get some photos maybe tonight.
Eagle H-beam rods, would be hard to bend....?
JE Forged pistons, they look rough, possibly salvaged?

I will get pistons pulled out of block after work today, give it all a good look.

Turbojack

I would replace all the pistons if they all have "dings" as you say. Some may be salvagable but is it worth the chance if they are not?

wrenchman

Knock @ idle could be a spun bearing.

Donman

I pulled the caps and all look great.

Donman

I have already decided to buy new pistons. I am at the point that I just want this repaired right, costs is not that much of an issue anymore.

waybomb

I once had the air filter screw in a Holley break in the threads, and the broken piece worked it's way down the threads and into the engine. made a horrible racket. Had threads marks all over the piston heads in the cylinder it got into.