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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?enter image description here

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    Are you sure the replacement pin didn't come that way?
    – DavidW
    Commented Mar 17, 2023 at 3:15
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    It looks like this is an open and shut case: my replacement pins do have this shape to them! There was no damage, it’s supposed to be like that. Thank you! Commented Mar 17, 2023 at 3:33
  • Another way to think about it is that it takes a lot of force to deform hardened steel. Plus you'd see that metal got pushed out of the crater to form a lip, rather than being all smoothed out like this.
    – Weiwen Ng
    Commented Mar 17, 2023 at 11:13
  • @WeiwenNg Considering the pin is heat-treated hard enough that it will snap off when bent, I don't think you would even get to see any plastic deformation.
    – MaplePanda
    Commented Mar 17, 2023 at 19:26

2 Answers 2

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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.

I haven't yet heard or figured out why Shimano emphasizes the strength of a chain joined in that particular spot is "enhanced." joining pin selection site

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  • I would assume the directionality has to do with how the chain interacts with the chainrings when performing a front shift. Not sure of the exact mechanism though--I can think of decent arguments either way.
    – MaplePanda
    Commented Mar 17, 2023 at 19:30
  • @MaplePanda That could be. I would assume there would be less lateral force at that point in a shift because the chain has either started to mesh with the next ring at the external link ahead of it (that it's attached to trailing) or, if the shift begins with the external link where the replacement pin sits in the lead, it already is a hair past where (possibly) the most dynamic aspects of the shift occur. It's in a bit of protected spot, one could consider.
    – Jeff
    Commented Mar 18, 2023 at 11:55
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They are supposed to be like that and I think it helps the chain tool to stay centered and not slide off to the sides.

The fact that it looks different from the other pins is actually a good thing. If you ever have to take off the chain again you are not supposed to push out a closing pin.

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