My first thought was the crank ground? I have found way to many reground cranks that still have grinder grit in the oil passages same goes with head ports. Just because they cleaned the part before the work doesn't mean they did it after. Clean your stuff.
You also need to run a wire brush thru the oil holes in the crank, even if the crank is brand new....
"If it was me" I would disassemble completely and clean everything at least 3 times plus all the suggestions before mine. I would also take a look at he bottom of the pan, look at the drain plug if it's magnetic, cut the oil filter and look at it, keep in mind what ever went through the oiling system may still in the motor.
Definitely looks like dirt. Years back I was helping my brother assemble a SBC. We had the fresh heads back on, turned it on the stand and glass beads ran out of the exhaust ports. STOP... take the heads off, back to the machine shop, they took them apart and cleaned them. Lucky no glass beads got into the engine. Another possible source is a dirty crankshaft.
Not that this has anything to do with debris floating through the engine, but shouldn't the holes in the cam bearings be at the bottom of the bore to line up with the oil passages from the mains?
No, you purposely rotate the cam bearings 90 degrees. Only cam bores that are not grooved do you line the holes up with the oil hole that feeds the mains.
You can do it now, or do it again later. But you will end up taking EVERYTHING back apart and cleaning it all again anyway so might just as well do it now. My first job out of high school was at a machine /race engine shop. I was the poor bastard that had to disassemble and hot tank and clean everything before and after machine work. You would be surprised how much effort it takes sometimes to get them truly clean. Especially the galleys. Don’t forget the oil pump and pick up too.
There's more than one way to line up SBC can bearing holes , you can net search & make your own choice .
Oh well,,,,,my practice has always been to line the oil hole with the oil galley . No exceptions ! The cam looks fine,,,,,the bearings don’t . How about the rod bearings ? Check them closely as well . Tommy
Have you ever read an up to date assembly manual pertinent to SBC can bearing installation or wondered why theres can circumferential groove under the bearings ?
No I haven’t,,,,but I’ve built several SBC from years ago . They had the grooves cut into the block,,,,and I never,, ever,,had a bearing problem. And usually the cam bearings looked new after thousands of miles . I still stand by my past experience . Maybe the new way works better . But how many millions of these things were made with the bearings done the old way ? Tommy
I've been assembling engines since 1962 , I try to keep current as there have been changes to procedures made( break in procedures are a good example) . we run far heavier valve spring pressures than we used to plus , bearing manufacturers have changed there recommendations. Its wonderful we're not all the same
Back in the previous millenium I traded for a "rebuilt" 327. Guy did it in his garage. Wiped the bearings in short order and actually started knocking. Same old story. Block was laying out in the weather and he drug it into the garage and assembled it. Probably had all kinds of critters living in the oil passages.
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