Thread: Main Bearing Failure

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No, mine are still holding up fine. My friend just bought a '73 Camero with a 350. It had a little knock to it, but it very quickly began making a horrible slapping noise. He took it to a shop because he isn't much of a car buff, and they diagnosed it as a thrown rod. The car ran rough because it had a cam that didn't match the motor, and it was still running on 8 cylinders. I figured it was a bad rod bearing. So, I suggested they get the GM's stock replacement 350 and transplant that into the car. Back to the point, we pulled the old motor and began disecting it only to find that all of the rod bearings were in good shape except for a few scores where dirt had passed through. There was hardly any discoloration except for a few shiny spots on the upper shells where wear had begun, but that was expected. I was a little worried, because I had just suggested they buy a new engine and this one didn't look like it had anything wrong with it. Well, there was one last part to check, the main bearings. I pulled the cap in the rear of the block and immediatly knew what was wrong. All of the babbit had worn off of the bearing and had been worn well into the copper mid-layer. I proceeded to pull the remaining 4 bearing caps and all were in the same condition. This motor wasn't very high milage as it had not worn a ridge into the top of the cylinder, yet. We did see signs of water in the oil underneath the oil fill cap and breather, but there were no signs of it in the oil pan. Also, the head gaskets appeared to be ok with only a slight browning between the center cylinders. So what I am asking, is what would cause such a failure? Most likely lack of lubrication, but I would also expect the rod bearings to be in pretty bad shape. No bearings spun, either.

So, anybody looking to buy a 2-bolt 3970010 350 with 882 heads for $300 ish? It's got a cast crank that may be turnable, but I cannot guarantee it. I saw no gaping cracks and there are no spun bearings. It has a .030 bore and due to the low milage a .040 might be enough to clean up the cylinder walls, but I cannot guarantee that without a mic. All of the main caps are there and I kept them in the order and direction they were originally.

Sounds to me like the block had water in it, the bearings froze, and started scouring where someone started it up without checking the stick first. engine turns, fires, mains stick to the crank, snap free and take part of the bearings with it. That engine is savable, but not really worth it. However, it would make a really nice table.

Detonation took out the mains! Too much timing or too much compression or bad gas.

Kinda pricey for a boat anchor, does it have cool valve covers ?

That's definatly a posibility, Typhoon. That engine had flat top pistons and they were running 87 octane. The advance at idle was 12-15 degrees. I would think detonation would take out the rod bearings first?