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Bob De Jonge
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I learned something new on my ride yesterday: http://connect.garmin.com/activity/113307208
Well, maybe re-learned something…
I headed out for a nice Saturday morning ride, thinking I would do a few hours. I ended up coming across an unexpected water refill (via a SAG wagon attached to a local ride going on), so I was able to go farther than my original water supply would have supported. There are no watering holes out in the backwoods area I was riding.
At around 60 miles or so, I had my first of what was going to be around 20 or so auto-shifts. For some reason, my bike was auto-shifting onto the small chainring periodically. Now, I have Di2 on this bike, so my first thought was that I had inadvertently tapped the left shifter. Well, after a few auto-shifts took place with my hands on the drops, and nowhere near the hoods or shifters, I started thinking I had an electrical gremlin of some nature. I started to think and diagnose as I rode — looking for shorted wires, or broken leads/connectors…
I was going up the last climb of the ride at around 90 miles (a shallow, maybe 3% grade), standing at the time (as I was heading for <5 hours for the hundered), when I had another auto-shift down to the small chainring.
I looked down, and my chain came off.
The master link pin had backed out, and the chain had come apart.
Suddenly, it all made sense —
My auto-shifting was taking place because the link had started to back out, and the exposed end of the pin had been contacting the front derailleur tripping the chain down onto the small chainring!
Some of you may be familiar with the Shimano 7900 chain. It has all hollow links, except for the master link pin. That pin is unique, in that it is not a constant diameter. Each end is the normal press-fit diameter, which is pressed into the chain link side plate. This diameter is only held at each end of the pin for maybe a millimeter. A very short shoulder. The middle of the link is a smaller diameter, a slip fit relative to the side plate hole diameters.
So, this is why Shimano recommends using a new link pin (not free BTW) every time you take your chain apart. Not surprising, as it is very touchy, given the narrowness of the 10-speed chain and the tiny press-fit shoulders on the link pin, to not have that pin pressed back in exactly right. Plus, one can imagine those tiny shoulders becoming worn after repeated assemblies. This issue would not exist in a conventional chain, with a constant diameter pin that is pressed in. With the Shimano chain, once the press-fit shoulder was loose in one chain link side plate, it was free to move all the way over to the opposite end. This was what was happening during my ride. The link pin would get pushed sideways, it would contact the derailleur, and my chain would dump onto the small chainring.
So, lesson here is: if you encounter this phenomenon, and have a Shimano 10-speed chain, stop immediately and press that pin back in!!!
Had I recognized this, I could've stopped at the first auto-shift, checked my chain and found the loose link, and pressed it back in without issue.
As it was, I had to remove that link, as one side plate was missing. I had to press out one of the hollow links (these ARE NOT designed nor intended for removal) and reassemble the chain. I had a chain tool along (another recommended bit of mass to tote around with you) so the pressing out/in wasn't the issue. I was wondering how the hollow link would react to it.
Well, I made it home, being only 10 or so miles away. I soft-pedaled the whole way, not wanting to stress that link any more than I needed to. But, I made it. —ruined my ride time and came in at 5:05 :(
Now, actually looking closely at my chain, I cannot find that link I pressed out! I figured it would be mushed out, deformed, etc. from that pressing, but no. So, what do I do? I may just go out today on the same chain to try it out. We'll see…
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Is anybody out there…?

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Had to have some custard pie for breakfast— NOM.
goes well with SBUX Italian Roast coffee
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juggling chain waxing and custard pie making… :)
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And, I had some cream in the fridge starting to go south. So, what then?
Of course!—
Custard Pie :)
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Blackberry pie construction on a rainy Sunday…
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I'm calling weekend.
Finally digging into some KBC Sesquicentennial special IPA…
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Cuckoo clocks are neat!
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Bleeding the brakes - trying out some ceramic pads…
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This year's blueberry jam vintage is perfect
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