Chain Snapping

[Cameron Newland]

My chain has snapped off twice in the last two weeks and I'm trying to figure out why. The first time it happened was when I was riding on flat ground and going about 20MPH. The second time, I was climbing a moderate hill going 20MPH and standing on the pedals and putting in a lot of torque on to the pedals.

Is this normal for a hub motor ebike? I had never had any chain issues in my first 2000 miles, and now in the last 100 miles I've snapped two chains. It seems a little strange, and I want to prevent it from happening again.

The only idea I've had for why it could be happening was that my chain often gets hops off the chainring and gets caught between the chainring and the chain guard. If I was applying a lot of torque to the pedals when the chain gets caught there, I could see how tension could build up on the chain and the chain could snap somewhere, however, I'm not sure if the chain got caught on the two occasions when it snapped off.

 

[EasyMotion Rider]

My chain has snapped off twice in the last two weeks and I'm trying to figure out why. The first time it happened was when I was riding on flat ground and going about 20MPH. The second time, I was climbing a moderate hill going 20MPH and standing on the pedals and putting in a lot of torque on to the pedals.

Is this normal for a hub motor ebike? I had never had any chain issues in my first 2000 miles, and now in the last 100 miles I've snapped two chains. It seems a little strange, and I want to prevent it from happening again.

The only idea I've had for why it could be happening was that my chain often gets hops off the chainring and gets caught between the chainring and the chain guard. If I was applying a lot of torque to the pedals when the chain gets caught there, I could see how tension could build up on the chain and the chain could snap somewhere, however, I'm not sure if the chain got caught on the two occasions when it snapped off.[/QUO

my eflow did that a few times so i sprayed everything with a lubricant and cycled the shifters, hasn't happened since. I was afraid to make any adjustments. WD40 is my friend!

 

[JoePah]

That is strange on a hub motor..

That fact that the chain is hopping off the chain ring indicates to me that your chainring is worn and possibly your freewheel. OR there isn't enough tension from the idler pulley to keep your chain in place.

I'd buy and install a high quality chain, the largest width that will fit in your freewheel. Then hand crank it and see if the chain is fully seated on all the teeth front and back, and check tension.

If it isn't seated take it to an LBS.. He will probably want to sell you some new parts!

 

[flymeaway]

Is this normal for a hub motor ebike?

No

Court J.

 

[Ravi Kempaiah]

I agree with what @JoePah said.
On my ST2, I am still using the original chain.

The only thing I can think of is few teeth on the front chainring or the rear cassette have worn out and some edges might have become sharper causing the new chain to break.

 

[Ann M.]

@Cameron Newland , check the adjustment of the derailleur; if a chain is hopping off a sprocket and getting stuck in a bash guard or chain guard then something's going on with the derailleur. It could be bent (especially the pulleys) if the bike fell over or was stowed leaning on the derailleur side. More likely, one of the adjustment limiting screws is not set right (good video for simple instructions on how to adjust). Worn teeth on that rear cog could also be a culprit, although at barely 2000+ miles they shouldn't be that bad.

It's unlikely that the original chain was the wrong length; however, it does matter to match the number of links when replacing with a new chain. Standard replacement chains might be a few links too long which could effect your shifting.

 

[MLB]

My chain has snapped off twice in the last two weeks and I'm trying to figure out why. The first time it happened was when I was riding on flat ground and going about 20MPH. The second time, I was climbing a moderate hill going 20MPH and standing on the pedals and putting in a lot of torque on to the pedals.

Is this normal for a hub motor ebike? I had never had any chain issues in my first 2000 miles, and now in the last 100 miles I've snapped two chains. It seems a little strange, and I want to prevent it from happening again.

The only idea I've had for why it could be happening was that my chain often gets hops off the chainring and gets caught between the chainring and the chain guard. If I was applying a lot of torque to the pedals when the chain gets caught there, I could see how tension could build up on the chain and the chain could snap somewhere, however, I'm not sure if the chain got caught on the two occasions when it snapped off.

Did you count the links to make sure they matched the original? Chain shouldn't come off chain rings. That needs to be addressed right away when it happens so things like what you experienced Don't happen.
Chains coming off at 20mph is always, always going to be a problem! You're lucky the chain broke and didn't lock the wheel or send you over the bars.
Did you look at your chain rings when you replaced the chain? On a motorcycle it is normal to replace the sprockets whenever you replace the chain unless they look like new. If the teeth are worn to a point the chain doesn't sit down on them correctly and will come off much easier and trash that new chain in short order! Aluminum sprockets on a racing offroad motorcycle can be trashed in a weekends racing. You need steel to last. A higher powered mid drive (is this a Bafang?) isn't much different than a small motorcycle if ridden hard.
I've got one of the new "HD" E bike chains (K something?) waiting for my Haibikes stocker to wear out.

 

[Cameron Newland]

Did you count the links to make sure they matched the original? Chain shouldn't come off chain rings. That needs to be addressed right away when it happens so things like what you experienced Don't happen.
Chains coming off at 20mph is always, always going to be a problem! You're lucky the chain broke and didn't lock the wheel or send you over the bars.
Did you look at your chain rings when you replaced the chain? On a motorcycle it is normal to replace the sprockets whenever you replace the chain unless they look like new. If the teeth are worn to a point the chain doesn't sit down on them correctly and will come off much easier and trash that new chain in short order! Aluminum sprockets on a racing offroad motorcycle can be trashed in a weekends racing. You need steel to last. A higher powered mid drive (is this a Bafang?) isn't much different than a small motorcycle if ridden hard.
I've got one of the new "HD" E bike chains (K something?) waiting for my Haibikes stocker to wear out.

I added a few links to reduce chain tension and that fixed the chain snapping issue, however, this bike model (2015 E3 Dash) in general has a problem with the chain hopping off the chainring even when the chain is properly tensioned. It tends to happen more often when the chain isn't properly lubricated, usually while shifting gears and going over a bump in the road at the same time. The idea solution would be to have another pulley between the chain tensioner/derailleur and the chainring that would ensure that any chain bounce is confined to the section of chain between the chain tensioner and the new pulley, and then also adding a chain guide on the top of the chain just behind the chainring:

http://www.pinkbike.com/news/Weeze-Chain-Device-Review-2011.html

Unfortunately, I think it costs a fair bit of money and time to build a custom chain-retention solution like this for each and every bike, so bike manufacturers must think it's overkill, but for commuter ebikes that get used often, I think having a definitive solution to the chain hopping off of the chainring is a must. I have a new ebike that I use now that has also had the chain hop off the chainring once and has caused some serious damage to the chain stay (steel chain grinding against aluminum!), so clearly I've got to find a solution for my new bike, too.

 

[John46]

I keep hearing that one should match the new chain with the old chain (same number of links). What about when you make a change to the chain ring. Isn't a larger or smaller one going to affect the required chain length?

 

[Nutella]

Like others have said, I'd check your chain length. Assuming it would fit on your cranks, you could put a narrow/wide chainring up front which should help a lot. Taller teeth and a tighter fit.

 

[J.R.]

I keep hearing that one should match the new chain with the old chain (same number of links). What about when you make a change to the chain ring. Isn't a larger or smaller one going to affect the required chain length?

This will help determine the proper chain for any setup.

http://www.parktool.com/blog/repair-help/chain-length-sizing