Unless it has a big obvious hole in the block! But I don’t see one...Yeah, you're going to have to do more than pull the pan. Pull some rod caps. Pull a main cap or two. Look for rods that are darker than the rest, that would be a good indication of a spun bearing. Nobody can just look at the outside of an engine and be like "ah ha!" and tell you what's wrong. Just because it's not locked up doesn't mean there aren't any rod bearings that are FUBAR. I've taken apart plenty of engines with spun bearings that would still turn with a wrench.
Yeah they do. That happened to me when I was a kid. It shut the motor down and all. I remember someone told me to take the belt off and see if it start up. Sure enough it did. I forgot all about that until you posted this.I have heard failing smog pumps sound like a spun bearing.
you will likely never figure it out from after all these years.