What causes this and how bad is it? 8BA flathead center main. This is the only one that looks like this. The others look very good and very little wear. If the cost were $30+ like a small block I would just replace it. But at over $100 for flathead bearings I am having second thoughts.
It kind of looks like imperfections from poring the babbit/bearing material.If it isnt actively flaking off it may be ok. Its not really in the load carrying area.
I can't imagine a builder actually installing a bearing that looked like that out of the package. Is there any sign of the material?
I've seen this happen from over heating and melting the babbit caused by not enough clearance or oil starvation. How does the crank and upper bearing shell look? It's possible the main cap has something wrong with it if the upper shell looks okay. Over tightening? Mismatched or warped cap? Cap installed backward? What size are your bearings? Maybe I have a pair.
Took apart a 327 years ago and found the same issue on several of the rod/main bearings, engine also had corresponding black "shadows" on the crankshaft. Did some research and found out the cause was "acid erosion" (due to a buildup of acids in the oil) meaning if one bearing shell is damaged they're all damaged, just hasn't shown up on the others yet. To be safe, my recommendation is to replace both rod and main bearings.
"You can pay me now, or you can pay me later" to quote an old ad for oil, that hinted at the consequences of taking shortcuts. Just sayin'...
Save your money now so you can turn or replace the crank later... The bearings is on it's way out....
My first thought was cavitation erosion, but that typically occurs closer to the loading zone, this wear is much closer to the crush relief area and looks like fatigue damage cause by excessive crush height of the bearings, or over-torqueing of the main bolts. As the others have said, I would replace them, and check the crush height of the installed bearing shell in the cap. Check this link, scroll down to Excessive Crush: https://www.speedperf6rmanc3.com/content/Engine Bearings.pdf
Acid etching is a possibility though it usually damages the overall bearing surface. I'm not sure if a bent crankshaft could be part of the problem. Looking closely at that bearing shell it seems like the wear pattern is a little wonky, like something is out of line.
Looks like a bearing that was “ to tight “ not enough lubrication and caused the loss side you have . I would double check all bearings and replace at least that one with a correct sized bearing . could have something wrong with the cap that caused it to squish more then the others slight lack of lube defective bearing etc etc inspect everything Someone else asked , why did you tear it apart in the first place ?
I would check the clearances with good quality micrometers or you can use Plastigage.......looks like that bearing might have been installed too tight.
It was disassembled to install a cylinder sleeve due to a crack in the cylinder wall. Engine was using water. I built the engine 15 years ago. and has about 50,000 miles.
I can’t guess what caused the issue, but as mentioned why go through the hours of pulling the engine, then taking it apart over a 100 bucks?
Always remember this . 100 bucks is nothing in Flathead dollars,,,,,,,replace the mains,,,,check the rods . By the way,,,you are right,,,,the crank journal looks great in that pic . Tommy
In Fla. I don't need antifreeze. I run water with "Water Wetter". The oil didn't get frothy but a little gray in color. I suppose that may have eroded the bearing. I believe most of the coolant went out the exhaust.
Ok so your fixing a crack and sleeve the engine ? Along with gaskets , fluids and everything else . Is this engine for the car in your avatar ? $100 bucks is small potatoes in the big picture .
$100 bucks is a bottle of a real good bottle of bourbon. Replace that bearing. Hold it, what the hell am I saying? Put that bearing back in and buy a bottle of Jefferson's Ocean Voyage 24. The engine may or may not grenade but you will be in a lot better mood to deal with it.
What has been said but 50,000 miles on a standard size crank - was it a NOS - just polished or what ?
Being the actual cause hasn't been discovered I would at the very least plastic gauge that specific journal if not all of them, rods included as I put the motor back together. I would also use the proper bottle brush to clean all oil passages.
The Jalopy Journal
