Technical One cylinder dull knock under load

Book just says bearing locating tabs are to face outward on the rods. The tab slots correspond with the rod numbers. The rod shown has the tabs facing inward.

 

Thank you for that, I absolutely will. Didnt know this, I'm trying to source some used rods, but may consider aftermarket rods if I find I need to replace several of these originals.

 

You know the rods are out so this is a bit of wasted time but........the back of the bearing, circled is a bit of rubbish on the left, on the right are some horizontal lines that dont belong, can you feel the horizontal mark near "US"? There is a heat mark near "US". You can see the machining marks of the cap on the bearing shell, up to where the horizontal marks are. cant see any contact above. What does it mean? the bearing wasn't in full contact with the rod surface, there is a bit of dirt that will have pushed the bearing surface closer to the crank, the horizontal marks look a bit like someone tried to force the bearing into the rod (maybe) or just some sort of damage to the bearing shell during assembly that may have also pushed the bearing surface up (if you can feel the mark then that's a yes). So maybe three issues caused the damage (rod out, dirt and the horizontal damage) . If I saw the lack of full surface contact Id be getting the rods resized (which I'm guessing you will ) I always look at the rear of a bearing shell for signs of other issues.

 

Crazy story! That would be pretty scary for me.

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It was a slightly crazy place to work, but fun.

 

Okay, this is hard to put words to but here goes. The second picture (of the crank) it looks like the rod above the crank on the left has a dark spot near the side of the rod where the notch for the bearing tang would go. If you look at the bearing with the copper showing it looks like the copper area is an equal distance from the tang to the dark spot on the rod. I would suspect the rod isn't round and the dark spot is a hot spot where the clearance is tight. Just a guess.

 

No dark spot on the con rod, but its 0.0083 out of round. I measured it so many times and I still dont believe it lasted as long as it did.

I'll be pulling the engine this week if I have time. We shall see what other surprises there are. The con rod with the issue is also in backward.....a sign of a true craftsman

 

I am not familiar with the unique characteristics of your engine, but on BB mopars, the faces of the rods are different. They are flat on rod-to-rod side, beveled on rod-to-crank side. This compensates for the fillet on the side of the rod journal. Backwards would mean even more issues. Check everything on this engine!
Example

 

If you do decide to use these rods again after having them resized, I would have the set balanced, maybe the whole assemble, but at least the rods. Big Block Mopar are the worst for out of set weights. I have seen as much as 40 grams out in a set of mixed matched rods, Ford included. And at that much out they will not be able to be balanced. Might even want to have them checked for weight before you do any thing with them.

 

Everything looked good other than the reversed and out of round rod.

Wrist pins are all tight and clean

Going to have the machine shop magneflux the rods, and hopefully I'll just find a used one and not have to have any resized.

It has already been bored 0.030 and piston to wall clearance is nice and tight with good cross hatch still showing.

 

fix the issues , wash it up and put it back together.

 

i have a new inn the box rod c7ae-b on the rod c3az-8200 a on the box if this will help you it is yours for the shipping

 

Was cleaning everything up and found this little melt down on my reversed rod #3 cylinder. All other pistons are absolutely pristine.

Never seen any meltdown on just one cylinder where a carburetor was involved. Multi port FI would be different.

This is what all the others look like with just a preliminary rince off with parts cleaner.

 

Just for reference before I took the heads to the machine shop to have hardened seats, guides, and new exhaust valves installed.

 

It may be the camera angle and lighting, but #1 intake (at least) looks to be sunk pretty bad.
Ask your machinist about all the valve depths and make sure the installed heights are correct.

 

Like the through safty bolt on the RH motor mount; I guess the LH could have used one too. Maybe the mount was making the noise.