Chain broken. What caused this?

[Tim Hall]

Just finished helping The Boy fit a new chain and cassette to his hybrid. He'd been complaining the shifting was a bit rubbish, and when he (lightly) washed the bike a couple of weeks ago I measured the chain, getting 12 1/8 inches for 12 links. So, yes, the chain had worn to the "change it now" point. However when he took it off we saw this:

(Excuse the rust). Two adjacent links with cracks around the river holes. Although it's rusty, I don't think the rust is a cause here. He hasn't lost enough metal thickness to get ito breaking point. It's a SRAM PC850 chain, so not some two bob rubbish. Theories please.

 

[User32269]

Stiff/jammed links caused damage?

 

[Tim Hall]

Which way was it running?

A good question. Unfortunately it was off the bike before it could be noted. I think left to right in the photo, with the pictured section being on the "top" of the run.

 

[raleighnut]

I'd go with @odav , rusted stuck links. Can't see anything else could cause that kind of damage.

 

[Sheffield_Tiger]

 

[Yellow Saddle]

Was the chain electroplated or just passivated (i.e. brown)?
Are those the only two links like that?
Don't throw the chain away yet.

 

[Tim Hall]

Was the chain electroplated or just passivated (i.e. brown)?
Are those the only two links like that?
Don't throw the chain away yet.

Ah, I was hoping you would show up. Chain was just passivated. As far as I can see, only those two links and only on that side (which I think was the "outside" , right of the chain). Chain retained for further interrogation.

 

[Tim Hall]

So not something chewing into those two plates then.

Don't think so. It looks more like a tear in the metal.

 

[slowmotion]

Don't think so. It looks more like a tear in the metal.

It looks like a tear to me too when the chain is moving right to left against whatever is causing the damage. There are two bright pins between the torn plates. That suggests that at least something is rubbing along the side of the chain as well. Another vote for some kind of stiff link problem.

 

[Tojo]

It looks pretty well fooked, for the price of a new chain give yourself and your bike a treat..... unless of course the rest of you're drivetrain is in the same abysmal state then you will be setting of a chain ( sorry for the pun ) reaction of renewing parts......

 

[I like Skol]

I have seen similar damage on my bike and it wasn't due to lack of oil!

www.cyclechat.net/threads/check-your-chain.147123/page-2#post-2865133

 

[Drago]

A nasty case of clefty that very nearly ended in deloopification.

I'm no expert, but I'm wondering if the rollers have seized against the pins, then as the whole lot turns the force then being transmitted has torn the links.

 

[Yellow Saddle]

A nasty case of clefty that very nearly ended in deloopification.

I'm no expert, but I'm wondering if the rollers have seized against the pins, then as the whole lot turns the force then being transmitted has torn the links.

Naaah. The rollers don't touch the pins.

 

[Tim Hall]

I have seen similar damage on my bike and it wasn't due to lack of oil!

www.cyclechat.net/threads/check-your-chain.147123/page-2#post-2865133

Ooh, that's interesting. That thread has a selection of links all showing similar breaks. Can you recall which direction your chain was travelling?

 

[Yellow Saddle]

Ah, I was hoping you would show up. Chain was just passivated. As far as I can see, only those two links and only on that side (which I think was the "outside" , right of the chain). Chain retained for further interrogation.

I've had that problem on a chain or two I owned as well as seen it on customer chains. Usually it is a plated chain that goes like that. The cause is hydrogen embrittlement, a malady that affects heat-treated steel in particular. Electroplating on top of heat treatment is particularly problematic but it can happen with just plain steel as well, as in your example.
The way the crack propagates has to do with the profile of the side plate and thus where the stress lines are. On my chain it went straight from the hole (it always starts there) and out through the shortest path. But, the path is determined by stress lines and the way the plate is stamped, determines that.

You can read about the problem here: https://en.wikipedia.org/wiki/Hydrogen_embrittlement

It is basically a fault at the heat treatment level, which is done after the plates have been shaped and punched, but before assembly.