Fino's Sbc Build

I think if you can hone it, put in new rings, bearings, cam, and timing chain it should be good for awhile. You've already lapped the valves and installed seals.

 

You can get away with cylinder taper but out of round is something you can't skate by with. Rule of thumb... no more than .010 taper and no more than .003 out of round. If past either that justifies boring and honing the cylinder.

You can check the cylinder taper with a compression ring and feeler gauge.

 

Check the bore if everything specs out ok. it could be it overheated and softened the spring of the rings.
I'ld guess it rightly should be bored 20 over and full rebuild.

 

well I am going to take my junk yard 350 and just run it,have looked at bearings ,they look good and can see it has been apart sometime,it came in a pile with a project car....so we'll see ,if it pukes I'll warm up the 327 and throw it back in....

 

The bearing is bad, the copper color is the base metal the babbit adheres to during manufacturing. The piston has signs of scuffing, if it continues it will transfer aluminum to the cylinder wall and nothing good happens after that. Ron

 

Normally lack of lubrication on the cylinder walls

 

That upper rod bearing looks like it had excessive oil clearance judging by how it wore.

 

That depends on the motor. The bearings are supposed to take the brunt of the wear, not the crankshaft. Often you can get by with new bearings and not turning the crank. You would need to measure the crank to see.

 

If you’d be happy with 20k miles, I’d have zero qualms about checking the oil passages, replacing the bearings with the same size replacements, new cam and new rings, a hone job, and run it. I feel like anything more than that (and anything less than an entire thorough rebuild), you’d be throwing money away. I feel like you’re at a crossroads; put it back together on the cheap and get a few good years out of it, or bite the bullet and build a new engine.

But... I’m no engine builder.
But I am good at getting way too much use out of old junk.

 

the sbc is very forgiving...

 

I agree with ITLKSEZ. It won't be perfect, but it should run well to at least 20,000 miles doing that. That #8 scuffed piston ain't great, but it will certainly run for may more miles. That cylinder probably had leaky compression rings so gas and carbon leakage was interfering with the oiling of the cylinder wall.


As for rod/main bearing clearance, generally the bulk of the wear happens on the soft bearing shell itself with very little wear the crankshaft surfaces.

Under normal operating conditions, the bearing surfaces do not touch. A "hydrodynamic" wedge of oil holds them apart and the shear of the oil itself acts as the bearing surface. This requires the proper clearances, oil pressure, and oil flow to work. The bulk of bearing wear happens during engine startup when there is no oil pressure the is direct metal-to-metal bearing contact. Contamination can cause the bearings to wear. As the bearings wear there is more space for oil to leak out leading to a drop in oil pressure. This extra clearance combined with lower oil pressure will cause the hydrodynamic fluid wedge to stop working in some engine load/speed situations leading to even more wear. Bearings will eventually spin when the oil film is working very poorly and there is excessive mechanical bearing contact. This leads to excessive heat/friction that can cause the bearing to spin.

Here's a paper discussing the how the fluid bearings work: https://kingbearings.com/wp-content/uploads/2014/10/Engine-Bearings-and-how-they-work.pdf

The main journals and large rod ends getting out of round and needing a line bore and/or resizing is more a function of stress relief over lots of load and heat cycles. It's not a wear thing. It's a usage thing. The block and rods will change shape over time.

In your case, if the bearings indeed took the brunt of the wear and the crank didn't, simply changing the bearings will bring the clearances back to an acceptable level. If the crank main and/or rod journals are worn such that a new bearing won't bring the clearance to an acceptable level, then the crank needs to be machined down to the next standard size that cleans up the journals (typically 0.005, 0.010, 0.020 smaller than stock). Thicker bearings shells need to be used to take up the space.

You can also get 0.002 undersized bearings that might bring the clearance withing spec with a slightly worn crank.

That is my understanding of crankshaft wear. I'm positive others here know more about it than I do and am not offended if they correct me.

 

Check for cracks. Clean it up and you can try dye penetrate.
I'm mostly seeing low oil / oil pressure issues.
Pull the galley plugs shove a brush through it and show us the gunk. Wash rinse repeat.
I'm still on the edge with the pistons.

 

Yes, you can get by with that old junk but in the end, you might get out what you put in.