I recently did a deep clean of my shimano 8 speed road bike chain by removing it from the bike. I used a chain tool to push out one of the pins (not the black one). I then replaced it with a 8 speed chain pin. I pushed it in with the same chain tool, and snapped it off on the other side. Everything appeared to go well, the chain links move well, the chain functions as expected. The only issue is that there is a dent left on my pin. Has anyone seen this before? Is this normal?
A Shimano replacement pin has a manufactured, slight concave shape on the end that the chain tool's drive pin interfaces with to push it home. Perhaps you didn't notice it prior to getting installed.
EDIT: Upon further review, I am incorrect in regard to the site of the joining replacement pin, and have deleted the bulk of my erroneous answer, replacing with the correct observations.
The OP's photo showing the rejoined chain in place does, in fact, show the correct placement of the pin as per the Shimano instructions. As has happened to me in the past trying to figure this out, I've mistaken the arrows on the left side of Shimano's illustration to infer chain direction. They do not. The illustration is a snap shot of a chain in the bottom run of it's lap. It thus would be moving right to left when in the forward direction. The pin selected for break & replacement should be the LEADING pin of the external link (the first one, and the inner link will be immediately ahead of where the replacement pin will go). The photo above shows the correct position of a replacement pin. The image below comes from Shimano's General Operations Dealer Manual, illustrating pin placement that enhances the strength of the chain.