Chain jumping off main chainwheel

[Swedave]

My 2 year old tongsheng tdz2 bike broke its 18 month old chain after jumping off the chainwheel and getting jammed. I replaced the chain this morning - just a regular simano for a 10-speed cassette and the chain jumped off after a minute or riding as I was changing gear.

Any ideas what I should be looking for here? It's not a problem I have seen before. Symptom of a worn main chainwheel? I don't think I have very high km on the bike (just a 20km round trip commute on mostly flat) so I would not expect any issues. Before the problem I was not getting any issues with the chain.

 

[fechter]

Possibly the chain itself. I had one where a link got stuck and didn't pivot which caused it to jump sprockets. Make sure each link pivots smoothly.

 

[hillslayer@]

I had that happening when hitting a bump a cheap chain guide that attaches to the down tube solved it.

 

[neptronix]

How's the chain tension? did you adjust the chain length to the right size?

 

[Zambam]

Used to happen to my TSDZ2 all the time (chain jump off chainring, not chain breakage), after hitting potholes or jumping off curbs, until I bought this (100BCD 42T) narrow wide chainring https://www.aliexpress.us/item/3256...st_main.5.7ae71802o690NZ&gatewayAdapt=glo2usa

Never happened since!

 

[amberwolf]

For most bikes, the most common reason for chain jumping off the front chainring is insufficient tension when going over bumps while pedalling, along with wear to the chainring that allows the teeth to push on the wrong part of the rollers and/or grab the side plates with the side of the teeth.

The tension problem can be caused bya chain that's too long for the available derailer wrap, or the derailer being misadjusted or the spring not pulling hard enough (damaged or made wrong, etc).

Another reason is frame twisting, often from cracked seat stays near the top of the stay close to where it joins the seattube, or from worn swingarm bushings.

A further reason with middrives could be chain misalignment from the front chainring being farther out to the right than normal, and using the inner rear sprockets, so that the wear from the extreme angle on chain and cahinrings / sprockets and the friction on them can cause the chain to lift up and then have sideplates land on teeth tips instead of beside them.


Don't forget that normally when replacing a chain for wear, you'd want to replace the chainrings and sprockets as well--especially on a middrive, which generally wears these parts faster than human power does.

 

[ak136]

What about front derrailleuer, is it properly set up? I see alot of people building mid drives remove it and commonly get their chain slipped off to the side of the chain ring

 

[Hillhater]

What about front derrailleuer, is it properly set up?

There wont be one on a TDZ2 drive set up.
FYI. ..for anyone interested in chain movement, there is some superb slo-mo video of the Paris-Roubaix cycle race last weekend where they race over cobbled tracks on road bikes. Chain movement is huge and control is critical for the racers.
One dropped chain and basicly your race is over.

 

[ak136]

There wont be one on a TDZ2 drive set up.
FYI. ..for anyone interested in chain movement, there is some superb slo-mo video of the Paris-Roubai cycle race last weekend where they race over cobbled tracks on road bikes. Chain movement is huge and control is critical for the racers.
One dropped chain and basicly your race is over.

Why there wouldnt be one?

 

[glennb]

Tight squeeze with motor and gearbox. Inner ring would mean narrower (less powerful) motor.

 

[Hillhater]

Why there wouldnt be one?

There is only one chainwheel with the TDZ2, so its normal to remove any front derailier components…..if threre were any to start with, since many recent bikes seem have adopted a single front chainwheel as standard

 

[lnanek]

If you had a front derailleur, you could keep it as a chain keeper. though. Just like you can keep a rear derailleur you never use just as chain tensioner.

On one of my IGH bikes where I didn't have a rear derailleur to use, I just used something from Shimano that looks almost the same, but without the cable:

https://bike.shimano.com/en-NA/products/components/pdp.P-CT-S500.html

Anyway, always good to check your chain line first. Hold a meter stick against your front chain wheel. If the stick doesn't point straight back at the gears, you need to space things in or out somewhere.

Higher speed chains are more flexible as well. I had to give up using thicker single speed chains in some cases. The half links used to help tension them when lacking horizontal drop outs interfere with narrow wide chain rings that retain chains better as well.

For my ebike where I never shift anyway I first ran the chain through one of these cheap tensioners:

https://www.amazon.com/dp/B0C8MQFF1L

Then eventually upgraded to this one after that one fell apart:

Amazon.com

Quite noisy, though. The Shimano is better.

 

[Chalo]

Also, inspect the chainring for damaged teeth. Even a single bent tooth can make the chain unship under load.

 

[Swedave]

Lots of good tips that might explain the original chain slip. But I have to confess that this time was 100% user stupidity. I routed the chain wrong at the rear derailleur.

 

[fechter]

I've done that before. Took a while to figure it out.