TallRider

I twice snapped my chain on my singlespeed. The first time I assumed it was a fluke and replaced the link, but after the second time I replaced the chain. It turned out the outer links were cracking - and there were a few more outer links on their way.
It's an old bushing-design chain, made by Sedis in France. I generally like old chains like this for singlespeed application, but I've never seen the plates start to crack before.
Is it possible this cracking has something to do with the tension on the chain? I'm running a tensioner with a biopace 42t ring on the bike. Doubt that causes particular tension issues (the tensioner hinges slightly through each pedal stroke to compensate for the changing effective diameter of the bioopace ring) but I suppose it's slightly possible.
More likely just old brittle steel (my default hypothesis).

Ferrous Bueller

Faulty chain. Steel for chains needs to have the right combination of flexibility, hardness and abrasion resistance. Not hard to mess up one of those. Ultegra chains were breaking like crazy a couple of years ago. Bad batch.

djb

have you ever soaked this chain in solvents for a long time? Someone on the forum did a test of this and strangely enough it ended up doing damage like this to the chain. I believe it was cyccocommute who took the time to do this, I only recall reading the posts but dont recall when it was, probably a few years back. Dont know if it was a dedicated thread or response within another (ie, might be hard to search for it)

Im pretty certain the chains he did tests on (leaving them in solvents for a week, or weeks) had exactly this type of crack appearing. I wouldnt have believed it, but he comes across as someone who would never make something up, and as I recall, he was pretty rigorous in his test, keeping track of time kept immersed etc.

Or, as you say, its old steel and the changing tension is playing havoc with it. who knows. Do look up what I referred to, it made for an interesting read in any case.

ps, is it just me or do others find the search function on this forum to be a total pain in the ...? Especially when if you reword things and begin another search, you are told you have to wait 30 seconds...then if nothing comes up, you have to wait again....frustrating. I usually just get fed up.

HillRider

The tension isn't doing it, it's no more under load than on a derailleur bike. As to the solvent caused cracking problem, it was due to a water-based "Mineral Spirits" substitute and the immersion time was months.

I agree it's faulty chain construction, either the wrong alloy or the wrong heat treatment. Was the second chain from the same lot number as the first?

BTW, wasn't Sedis the developer of the first bushingless chain back in the late 70's or early 80's? How old are the ones you are using anyway?

djb

HR, thanks for recollecting better than me. Seeing this did make me wonder if at some point this chain could have had the same thing done to it-Ive never had a chain break on me (touch wood) so only thought of that odd occurence with the mineral spirits.
Tallrider, did you buy these chains, were they given to you?

hotbike

Yes. Biopace Chainrings were NEVER meant to be used on a single speed bicycle. I had Biopace chainrings on my Peugeot Canyon Express 18 speed Mountain Bike, back in 1986.
What your doing is putting excess tension on the chain. The Biopace Chainring, in case everyone doesn't know, is Elliptical , Not round. So when the pointy part of the egg-shaped ring is in position, it's tighter.
Normally, the springs and idlers on the rear deraileur would take up the slack, but a single speed doesn't have a deraileur.

EDIT, Well, it looks like you do have a deraileur thingie, to take up the slack. I was thinking of something different when you said "tensioner" I was thinking of the BMX style tensioners.

Airburst

I've definitely seen cracked links like that on a bike at the co-op, I think it was an old 10-speed Raleigh from some time in the '70s, it might have been the same kind of age as yours. We just replaced the chain with a new 5/6/7-speed one and chucked it, since it's definitely the chain that's the issue - nothing you can reasonably do to a chain while riding will do that.

Also, slightly off-topic, but Sheldon Brown apparently managed to run Biopace rings on singlespeeds without chain tensioners, if you wanted to give it a shot and save a bit of weight.

TallRider

I figure the metal may have been a bad batch of chains, but more likely it became brittle over time. it's possible I'd left it for too long in mineral spirits, but not overnight, let alone months at a time.
I the steel somehow degraded over time, though I'm not sure of the chemistry that would cause this.

The chain is used, which usually doesn't cause any problem for me. But this one is particularly old, as HillRider figured. I took the chain off a 1970s Peugeot that is French to the core (other than the Reynolds 531 frame): Mafac brakes, Simplex drivetrain, Stronglight crank, Sedis chain. So the chain, while fairly un-worn (in terms of "stretch"), IS close to 40 years old. Here's a pic of the bike.


As to biopace on singlespeed without a spring tensioner, it's not perfect. I tried it (based on Sheldon's advice) but biopace does create some fluctuation. While the number of teeth engaged is always the same (Sheldon's point) the angle of chain from the rear wheel to the chainring does vary as the outer diameter of the chainring changes with rotation. So you'd need to be careful to adjust the chain to max allowable tension when the chainring is oriented to max vertical-plane diameter. This means the chain goes a bit slack at other points during the pedal stroke.
I like the feel of biopace rings while pedaling and the spring-loaded tensioner allows me to run it on a singlespeed. Note that the tensioner does hinge a bit with each pedal stroke as it adjusts for the rotation of the biopace ring.

and yes, I find the search function to be frustrating, compared to, say, google.

DannoXYZ 

Personally, I like the Biopace rings rotated 144-degrees forward. That really evens out the naturally lobsided pedal strokes. You can really hear the difference while on rollers. The wrrrump-wrrrump-wrrrump rhythm becomes an steady vvrrrrrrrrr.... When oriented in the stock Shimano orientation, the sounds are even more lobsided than with round chains.

JiveTurkey

You can use Google to search only within this site. Put "site:bikeforums.net" in front of what you want to search for using Google. If you want to limit it to just the Bike Mechanics section, use that URL. This works for many (all?) websites.

cyccommute 

Looking at your picture, I see crystalline foreign matter that looks like salt. If it is salt, that could lead to cracking of the steel

FBinNY 

This is one possibility, though it's usually accompanied by visible corrosion. (doesn't have to be).

But I lean toward excess tension because you use a chain tensioner. These things should almost be banned, or at the very least renamed chain slack adjusters. A chain should never be under tension. The slack should be taken up until there's a minimum vestigial slack remaining at the tightest spot (even round rings aren't perfect so runout will vary the chain slack as you pedal).

A chain that's actually tight wears very fast if you're lucky. If you're not, it can bend axles, break dropouts, fold chainrings, or stress crack plates.

BTW- steel doesn't age. If it did the Brooklyn bridge would have fallen down long ago.

Airburst

It's a swing-arm tensioner, one of those "half a derailleur" things, not a banjo bolt tensioner like you'd have on a BMX. No way in hell that thing had enough spring tension to break the chain!

FBinNY 

Absolutely, it couldn't break the chain. But if the OP pulled the wheel back based on the BioPace ring, he could have straight run tension at the tightest point.

Otherwise, I'm with Cyccommute, that the chain was chemically comprised,most likely by chlorine ions.

Airburst

Looking at where the wheel is in the picture, there seems to be a fair bit of travel left in the tensioner arm, and seeing as Sheldon managed to use a Biopace ring on a singlespeed with no tensioner, they clearly don't generate huge amounts of variation in the chain tension. I doubt the chain could pull tight whatever happened with the cranks, even with the wheel all the way back in the dropouts.

TallRider

Danno, interesting about the pedaling smoothness. My pedal stroke may well differ from yours, but I'll give the rotated-two-bolts-forward a try. It's easy to switch up on a singlespeed.

TallRider

@cyclocommute, The crystalline stuff on the chain is dirt or sand because it fell off the bike when it snapped.

FBinNY and Airburst, the chain tensioner is mostly a slack-taker-upper. Adds in more tension than a derailer, but it's not gonna change the max force through the chain at all. Is there a better word than "chain tensioner" for what I'm using? It's like a more-firmly-sprung derailer.

So there may be something chemical going on with the chain, but I don't know what. I probably cleaned it in mineral spirits, but wouldn't have left it in overnight, let alone for weeks or months.

FBinNY 

OK, I withdraw my references to chain tension being a factor. Single speed chain tensioners are a sore point. Not spring idlers, like the OPs, but the banjo type so often abused by new SS riders who take out 100% of the chain slack.

As for the breakage, another possible cause is a defective chain because of tolerance issues. Chain plate holes are slightly smaller than the pin diameters, and the chain is held together by interference fits. This is close tolerance stuff, if the hole is a hair big, the plates walk off the ends of the pins, but if a hair small, or if the plate temper is a bit hard, the radial stress exerted by the pin cracks the plate. Chain makers are pretty careful about this, but compost happens, and chains prone to plate breakage can and do slip out once in a while.

Also corrosion can contribute by changing plate ductility, or by swelling the pins. If the chain spent lots of time dry, the pin could rust inside the plate. This would be visible if the pin were pushed out and examined.

In any case, I have a simple rule. If I see just one cracked plate, the whole chain is suspect and discarded.

djb

like I said, Ive never any chain problems, but I will sure remember this line. Seems like a pretty good common sense approach.

cyccommute 

Mineral spirits won't hurt the chain. The experiment I did was based on soaking a chain in water based "green" mineral spirits which is more detergent than anything else. I soaked the chain in salt water for several weeks to get the plates to crack. Here's the link. Although the whole thread is interesting, if you want to jump to the chase, look at post #118 on page 6.

Your cracking may not be corrosion related but is related to the way that the chain was made. The stamping process puts stress risers on the chain and then using it in a single speed application with the higher tensions involved could cause the plates to crack in the same manner and location as the salt cracking occurred.

djb

"link" boo-boo there Stuart. Leads back to this page.

the salt water reference makes me think of a CGOAB journal of a woman who biked through Central America and took a boat from Panama to Columbia. Her bike was strapped on the side of the boat as-is and Im pretty certain she had all kinds of salt issues, including a snapped chain afterwards (I might be remembering wrong, but I think so)

cyccommute 

Oops. Fixed