Mr_Pickles3

My sister and I were cycling along tonight on my tandem when suddenly, after a gear shift, the chain just snapped. There wasn’t any warning or feeling to suggest it was going to break beforehand.

This is now the second time this chain has snapped in as many months, even after I repaired it carefully the first time. I’m new to tandeming and this is really off-putting (especially given other mechanical problems I’ve faced since restoring the bike)

Is this a common problem with tandems? Have I been using the wrong type of chain? The chain used was a normal 5 speed (the tandem has a 5 speed freewheel).

Barry2 

If you are fixing the chain by forcing the original (or a substitute) pin back into the chain, I'd suggest fixing the break with a quicklink instead.
Oh, and did you buy a name brand quality chain?

Barry

ClydeClydeson

Tandems are extremely hard on their moving parts. Everything sees double the load what the same part on a single bike sees.

Three things to consider:

Check that all the teeth of the cogs and chainrings are straight and not bent. A bent tooth can put a bend or kink in a chain link that eventually causes it to break apart.

Old drivetrains were not intended for shifting under load. Trying to force a shift on an old drivetrain without easing up on the pedals can damage a link and eventually result in chain failure.

The most common cause of chain failure with modern chains (usually 7 or more speeds in he rear) is improper assembly. If a modern chain is reassembled by pushing an old pin back in it will almost certainly fail over time. Modern chains are sold with 'quick links' or a special re-joining pin (SHimano) so you don't have to reassemble with a pin that as been pushed out. A 5 speed chain that does not have its pins flush with the side plates can be rejoined with the pin you removed, but you still have to be careful to put it back together evenly so it isn't stronger on one side than the other.

trailangel

Where are you getting these 5 sp chains?

Andrew R Stewart 

Very good reply and pretty spot on. I'll add the the peak loads that tandem chains see can be much higher then mere doubling of a single bike's. For the steady state loading doubling is not a bad assumption but when shifting the greater inability to control the stoker's power output means that tandem chains see a lot more "jam shifting" even if the captain is an experienced rider and knows how to soft pedal during shifts. The stokers reaction to the "shifting" notice the captain said (and had better be communication or the bike and the desire to ride it will both fail soon enough) will be delayed and sometimes nonextant at all.

When I sold and serviced tandems a lot we suggested replacing final drive chains about twice as soon as one would on a single.

Not mentioned is the timing chain and rings. While they sees less peak loads then the final drive does they wears both with power forwards as well as backwards. It's often that one rider is powering the other's legs so the wear on the ring teeth is eroding on both sides of the teeth. In time the chain will more easily derail when under high power moments. It's for this reason that routine checking of that chain's tension (ideally zero and with very little chain bounce) is important. Andy

Mr_Pickles3

Thanks for the advice everyone

The chain wasn’t branded, which is probably something to do with it. I have a new KMC chain at home I can replace it with so hopefully that will be more reliable (it seems to have thicker plates).

when I say 5-speed, I mean a chain labelled 5/6/7 speed!

My repair was by using an orignal pin and joining the loose ends of the chain together, which I thought would be okay (the powerlink snapped the first time), but evidently not. Looking at the chain, it seems to be much looser with side to side movement – reflecting, I imagine, the extra load on it when shifting.

The tandem doesn’t get thrashed too much; it’s used for riding around the local area and is a restored Peugeot with mostly original parts. I’ll be checking the drivetrain setup more closely.

Andrew R Stewart 

This, bolded, is poor chain assembly for a modern chain. Pretty must all chains labeled 5,6,7 these days have peened pin ends. So when the pin is removed (by purpose or incident) the peening scrapes open the hole in the side plate, larger then what the pin retention design wants. A classic mistake and one we still see often. This is why so many will use a connecting link instead of reinstalling an original or even proper replacement pin. Andy