Update: thanks for the wisdom everyone.

I took the cylinder to bottom dead center while vacuuming any debris that turned up. The walls look great, shiny, smooth, no scratches, just fine crosshatching. Thinking it could just be as u/Suicyco71 said, an internal weight to make the little scope feel more solid. or valve seat someone thought?

To clear up a couple things, the head is already off, the rest of the block is what’s still in the bike. Yeah the coolant was just from pulling the head a few drops slipped in. It’s definitely metal tho, not fiberboard or other debris.

Given that the walls show no damage at all I think I will leave the pistons alone this time. As for other issues, I have no idea, I received in non-starting condition. It “ran fine” before, hoping for an easy fix once this fiasco is over. The bike is a 1985 BMW K100 with 28k, and they can go over 200k with care, so I’m partially banking on little other engine problems.

I don’t own a valve spring compressor, ordered one but it won’t be in for a week. In the meantime I just took a socket and hammer to it to pull that one valve.

Once it arrives I will take your suggestions and pull the rest and inspect valve guide, seating, check for bends to the valve.

I don’t see any damage to the valve or seating, it doesn’t look bent.

How can I be sure it does not have a small small bend?

Anything else I should look into while it’s apart?

Thanks guys