Pardon me for the pun, but a chain of people have been linked with Shimano chain failures.
Consider this an update to the my first post where a reader alerted me to his concern that large batches of Shimano's Ultegra chains have been failing recently. The said person worked for a cycling magazine so he was probably witnessing this first hand with his access.
In that post (click here if you haven't read it), readers and me agreed that a possible suspect may be related to heat treatment that may be causing the links to become brittle. However, at this point, there's insufficient test data to back that thought.
As to what the heat treatment protocol it is that chain links undergo is not within my knowledge. If there are industry insiders reading this who want to help provide insight, please feel free to join in with a comment.
Within days of writing the post, I obtained news of more instances of failure.
Case 1 : This Shimano 6700 chain, used by Roger failed after just 2500km of use. He wrote to me that he had kept it well lubricated and had never cross-chained excessively (and never with force), yet it broke in the exact same manner as in the images that were shown here. According to him, he had never broken a chain before and would usually swap them out only after 10,000km or so. Apparently, he had them sent back to Wiggle and when Shimano was contacted about it, they didn't recognize the problem.
Case 2 : A blogger with Team BBC in Baltimore, Maryland posted a tweet showing his Ultegra chain that broke in a matter of just 7 days. According to him, it was installed as per the instructions yet he was caught by surprise when he found cracked side plates while lubing the chain today. He also remarked on Twitter that another racer from the same area fell and lost some skin after his Ultegra chain broke while he attempted a "track stand". The following pictures were posted on his blog.
Case 3 : I received a quick note from Jonathan Judd yesterday telling me his story. He did not have any pictures for me. I quote him :
"My Ultegra chain broke 25km into a ride on Saturday. That was the first ride the bike had ever done - brand new. I had climed for around 300 meters in altitude gain without any problems. It was after the descent when I dropped onto the small chain ring (under virtually no pressure) that the chain broke. Initially I thought it had over shot the small chain ring but then I saw it hanging down into the road. Luckily I had a chain tool and spare connecting pin. But 25km is shockingly poor!"
Shimano has not recognized the problem nor have they issued an official statement in spite of multiple failures. It is suggested that they do a root cause study and issue a recall of product from the market if it is defective.