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Chain damage - cause?
While cleaning my chain today, I noticed the damage in the attached pic. I'm at a loss to explain how it happened; I haven't seen anything like it in 20 years of maintaining my own bikes. Does anyone have any ideas? 
If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.
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6 comments
Sabotage? Excessive life insurance policy payout...?
It's possible you have accidentally hit the front shifter for the front mech with the bike stationary and the spring pressure has trapped the chain between the teeth and the cage and bent it. The pressure from that can have a good go at popping the side plate off the pin, I have also seen that kind of damage done when people have over done trying to ease a stiff link before now.
Having said that it's not unknown to get a chain trapped on a tooth and split the link they way the others have suggested.
It could be your mech like mkultra said
My limits where a bit off and I did similar damage while riding when It caught on my front mech as I shifted up on the rear
The damaged chain has around 2,250km on it, in reasonably dry conditions, and was regularly cleaned and lubed - it measures 132.4mm across six rollers, so just on the verge of exceeding Campag's wear spec. Sprockets and chain rings have 4,000km on them. I replaced the chain as soon as I saw the damage and there's no skipping.
The chain had been off for degreasing before I spotted the problem, so it's possible that I refitted it the other way round, i.e. the damage could have occurred on the inside.
Thanks for the advice and possible causes, I had no idea that a tooth can get between the inner and outer plates of the chain. I assume this happens when changing gear while mashing the pedals?
As above, but with the damage on the outside I'd say that happened on the chainset rather than the cassette.
It looks like as the chain traverses the cassette one of the teeth has got in between the plates, causing the above damage
Question would be how old is the chain and drive train?
Change the chain immediately and check the teeth thoroughly and replace if showing signs of wear or bent