Shimano chain - broken twice

[Cyclewala]

This is odd. Two rides, and two broken chain links. Shimano HG53. 650 miles in total.

Fixed the chain with a quicklink the first time (Friday) and carried on riding for another 20+ miles.

The following ride (today) chain broke again 6 miles in. Different link. But, on both occasions I was climbing a steep hill - sitting, not honking.

Bike runs Alfine 8 hub so no poor gear changes to blame. Is cleaned and lubed regularly. Originally installed using Shimano special pin and not been removed from the bike since. Neither of the breakages were at the pin.

This is the 3rd chain on this rear sprocket, the previous two did c. 4500 miles each. I've done 3 chains to 1 sprocket several times previously.

I'm putting it down to a duff chain and going to replace.

Any other possible causes?

[gregoryoftours]

I'd check all of the teeth of the chainring and sprocket for any damage. Are you running a tensioner or setting chain tension in horizontal dropouts? If the latter possibly chain wrong tension? The chainring mounted on the crank spider especially will rarely be perfectly round and even, there will be a spot where the chain is tightest. With no tensioner it needs to be set up to accommodate this tightest point. Are the sprocket and chainring secure on their fittings?

[David9694]

Something somewhere is broken or severely out of alignment - you need to find that thing.

[alexnharvey]

What broke and how? Was it a outer link plate cracking, pin pulling out of the side plate or something else?

[Brucey]

CN-HG53 is made by KMC for shimano. It should be similar in quality to a basic (unplated) X-9 chain, both having chromised pins.

Running multiple chains per sprocket means that you will be running on a worn sprocket; depending on how worn the sprocket is, it may just impose abnormal loads on the chain, or it might even be noisy under load. Worth double-checking your chainline too. Another thing to check is the chain tension; if slightly slack it can get to a point whereby it can start to derail, but break in the process; either tighter or slacker is an improvement, because the chain will either not want to come off or will manage it without damage respectively.

CN-HG53 uses bullseye riveting (like 10s,11s etc chains) which means that there is a lot more residual stress in the side plates than in many other chains; if the swaging is slightly overdone this makes chain breakage more likely. In the winter, road salt greatly increases the chances of getting SCC too.

So the chain might be a duffer (I don't think there is a chain brand which has an entirely unvarnished reputation for reliability, is there...?); then again it might have been helped on its way by a worn sprocket, other setup issue and/or winter conditions too. In any event two breakages is a big hint that all is not well. FWIW you can use Sturmey Archer sprockets on shimano IGHs and they are sufficiently cheap that you can have a new one with every chain.

cheers

[Cyclewala]

What broke and how? Was it a outer link plate cracking, pin pulling out of the side plate or something else?

On both occasions it was the outer plate at the pin joint and on the chainstay side.

Drivetrain runs silently and chainlike is straight. Chain tension is always set at the recommended 12mm.

I suspect a dodgy chain exacerbated by winter riding and possibly a worn out sprocket.

Will have a good look this evening when I dismantle it.

[Cyclewala]

FWIW you can use Sturmey Archer sprockets on shimano IGHs and they are sufficiently cheap that you can have a new one with every chain.

cheers

Really? Not doubting you, I thought it had to be the Shimano specific for Alfine as it has a plastic side plate and the sprocket itself is shaped differently on one side.

[Brucey]

the plastic guard only does anything if the chain is so slack it is trying to climb off the sprocket, and then not much. Other IGH sprockets are similarly dished and give the same chainline.

cheers

[Cyclewala]

Cheers Brucey. You're right, there is a stark difference in price between Sturmey and Shimano sprockets.

[Cyclewala]

Update:

Took everything apart, nothing untoward in the chain, sprocket or chainrings - i.e. no bent teeth.

Chainring has little wear but looks ok.

Old sprocket (top) has some wear when placed next to the new one (bottom). Teeth are narrower and the valley is deeper and flatter. Will be installing new sprocket.

What does the panel feel? Is the sprocket worn beyond acceptable tolerance and if so, could this be the cause?

[Brucey]

I'd expect that sprocket to be 'very noisy' with a new chain when under load.

Whether that would be bad enough to cause the chain to break is quite another matter though.

cheers

[Jupestar]

Has the chainring been turned around?

[Cyclewala]

Has the chainring been turned around?

No. The chainring has not been turned around. The sprocket only goes on one way as it's dished.

I think it's just a duff chain. This model, CN HG53 is branded Shimano but made by KMC and there have been some reports of premature breaking.

[andrew_s]

Duff batches of chains do happen occasionally (any brand).
If that's happened, you would normally be able to see a few extra unbroken cracks at the outer side plate pins (cleaning may be required)

[Jupestar]

Has the chainring been turned around?

No. The chainring has not been turned around. The sprocket only goes on one way as it's dished.

I think it's just a duff chain. This model, CN HG53 is branded Shimano but made by KMC and there have been some reports of premature breaking.

Just in the photo the wear on the chainring (not the sprocket) is the opposite way I would expect. Maybe I’m making out the image wrong.