I think I detonated engine, please HELP
 

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... :eek: 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!

Re: I think I detonated engine, please HELP
 

post clear pics of the pistons

Re: I think I detonated engine, please HELP
 

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.

Re: I think I detonated engine, please HELP
 

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.

Re: I think I detonated engine, please HELP
 

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.

Re: I think I detonated engine, please HELP
 

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?

Re: I think I detonated engine, please HELP
 

Knock @ idle could be a spun bearing.

Re: I think I detonated engine, please HELP
 

I pulled the caps and all look great.

Re: I think I detonated engine, please HELP
 

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.

Re: I think I detonated engine, please HELP
 

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.

Re: I think I detonated engine, please HELP
 

not good..sorry to hear it.....that is why I always suggest going up one notch on octane in an offshore engine ...if it says 87 I run 89.

my .02

Re: I think I detonated engine, please HELP
 

My pistons are true flat-tops with one relief, with Merlin heads, I think I am at 8.9 : 1 compression ratio. I am running a 50/50 mix of 89 and 93 (91 octane). My timing is conservative, I shouldn`t have had octane issues.

Re: I think I detonated engine, please HELP
 

Unless you got a tank of bad gas...and that does happen...lots of crap going on these days in the gasoline buiness.

Re: I think I detonated engine, please HELP
 

many years ago I had a similar condition on one of my bbc's One plug tip was missing and circulated through out the motor. It ended up that the cyl.head had a small crack in it and the spray of cool water cracked the plug. Probably not your condition but it may pay to check out the heads real close anyway!! good luck keep us posted!!

Re: I think I detonated engine, please HELP
 

Did you check the rod bearing on the cylinder with the broken plug?? Detonation can flatten rod bearings due to the extreme forces as the piston is forced down as the rod is pushing up. Are you running inconel exhaust valves? If not I would invest in them this rebuild.

Investigate the fuel pressure when you get the motor back together. The loss of rpm was likely running out of fuel which caused detonation due to the high a/f condition caused by low fuel pressure. Check the fuel pump, the fuel filters etc. and make sure the fuel pressure stays greater than 4 psig at the carb with a NA motor. :(

Re: I think I detonated engine, please HELP
 

All rod bearings look great.....

I`m replacing the fuel pump with something more substantial.

Re: I think I detonated engine, please HELP
 

I have my fuel pressure set at 7psi on a carbed engine. Anymore than that, and you will overwhelm the needle/seat.

Re: I think I detonated engine, please HELP
 

I took my engine parts to machine shop this morning.
Here`s the verdict:
Engine ran lean, comb chambers very hot, #1 cylinder dropped exh valve seat. Seat bounced around through engine, damaging tops of pistons.
I need new pistons, rings, rod brgs, mains, gaskets, new exh valves, valve seat, mill heads, clean block, hone cylinders, valve job, valve seals, polish crank......about $1500 plus my labor.

Re: I think I detonated engine, please HELP
 

I would double check your intake valves. I bet you have some tulips!

Re: I think I detonated engine, please HELP
 

I`m having this shop inspect EVERY engine part carefully. He knows it`s in a boat and that I run it hard.
This guy is the guy who built all of Eddie Hill`s engines back when he raced drag boats and Top Fuel dragsters. He knows his stuff.

Re: I think I detonated engine, please HELP
 

I was going to suggest that something found it's way into the cylinder bounced around, broke the electrode before finding its way to another cylinder... looks like you found the culprit. I did not think the electrode caused all of the damage you were describing, we have melted way too many of those off with N2O and not done that type of serious damage.

Re: I think I detonated engine, please HELP
 

5800 rpms? :eek:

Re: I think I detonated engine, please HELP
 

that is just a warm up for a small 498"....

how about 604 inches at 6k+.... :D :drink: :eek:

Re: I think I detonated engine, please HELP
 

What did the gps say?

Re: I think I detonated engine, please HELP
 

141 i think.... :D