Have a gen 3 6.0 that was machined ( shop closed and owner retired) but I was ready to assemble the top end and realized on one of the cylinder sleeves had a line down the side and that if I rub my finger nail across it it’ll barely catch on the tip of the nail. Had another local Machine shop check it out they told me it would be fine. However as it’s my first build am second guessing it. The engine has a little torqstorm supercharger I bought for it so it’ll see a little boost which also is why I’m wanting to confirm. What do you guys think? Cracked or scratched and if so would there be a way to smooth it down a little?

engine has never been ran spent about two months on the engine stand while we moved.

That's a scratch. I've never seen a crack perfectly straight like that. You'll be fine

Looks like a scratch from a ring that wasn't filed properly of burrs.

Any way to tell if they need to be replaced? Engine turns over smooth and doesn’t bind up at all.

Ok thank you!

I would fix it.. looks like ring burr.

Last thing you need is it to catch and snap the ring or piston

A reason why you should take a little off the corners.

Very old points file for this.
Small, and easy to use.

Yes sir, it was a tip I got from a Pro so thought I'd share even though I've read where not to do this but I found that it helps keep the corners of the rings from causing issues. Sure you may have a little more blowby but so what.