chain and surface rust

[scotsbikester]

No, not metal fatigue but user error. Your chain did not break in outright tension but in a bit of cross-chaining on the cassette where the chain was halfway between two gears and you applied pressure. If you can recall, you'll remember that the chain burst open and the sideplate separated from the rivet.

Had the chain broken in tension, the sideplate and rivet would have remained in place but the sideplate would show a break at its narrowest part - that part exactly in the middle between the two rivets, with a teensy bit of elongation.

That's interesting. I'm (relatively) new to derailleur bikes, though I did build this one myself. It's a 9 x 3, and I tell myself, and other cyclists, that it means I have 3 chainlines which are dead straight. And as long as I'm disciplined about changing chainrings, it's never more than two sprockets "out of line".

I try to let off the pressure to practically nothing when I change, certainly when going up. Sort of pedalling at the same speed as the bike, but with barely any pressure. But I thought that was more to ensure a smooth change. I didn't realise it could possibly cause a broken chain.

Thanks for the info.

 

[Yellow Saddle]

Aircraft manuals recommend throwing out various items after X hours of use (even if they're showing no signs of wear and tear) and fitting brandnew ones, so perhaps we should dump our chains every 6 months or so and replace them with brandnew ones to be on the safe side?

I've seen this approach taken by well-meaning mechanics and participants in multi-stage mountain bike racing. Unfortunately it is a flawed theory. A chain that's already done one stage of racing without breaking, has proven its mettle and statistically will be less prone to breakage than a brand new one. Reason being, that a significant number of breaks are caused by user error, particularly so if the chain is finished off with a pin, rather than a quick link. It is easy to botch a pin insertion without noticing - until you've ridden a couple of kilometers.

If the chain is still within wear spec, leave it alone.

 

[Tail End Charlie]

The only time I've broken a chain was when I massively cross chained (I was in big big) so t was my own fault. In my defence I was very tired towards the end of a long ride. No great shakes as I did have a chain tool with me, but I could have done without it happening, as I needed to catch the last train home.

 

[biggs682]

Has anybody ever had a chain snap?
It's only happened to me once in many years of cycling, I was out for a bike ride and turned onto the lower slope of a hill and put the pressure on the pedals and SNAP it went, and I hit the deck, no injuries.
I'd always kept the chain well oiled and rust-free, so it must have been metal fatigue or something.

Yes on my single speed Pollard as I neared the crest of a hill and 6 miles from home