Chain jumping off front sprocket

[Atlav4]

Hi gear change seams slick and smooth and have no problems whatsoever on roads but when I occasionally ride on pavements and bump down then up a series of low kerbs the chain jumps off the front chainring. Although not every time and I don’t believe it to be speed related, it’s occurred too often to be a minor niggle. Question ‍ is there a small adjustment to chain tension that can be carried out to rectify this conundrum but which leaves the gear change efficient. Thanks bikes a woosh Faro closing in on 1000 miles since purchasing, gears are 8 speed shimano acera.

 

[vfr400]

The problem is the lack of front derailleur. You need a chain guide. Take your pick:

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These are cheap it it fits your frame tube and reaches the chain:

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[Atlav4]

Thanks dude looks like the answer and easily fitted, cheers

 

[soundwave]

chain is to long remove some links one at a time until you can still get all gears and not have the chain fall off the front sprocket.

if you put it in the smallest gear on the rear there should be no slack in the chain and a bit of tension in the rear mech pulling it forwards going up the gears to the biggest sprocket.

you might also need to index the gears after doing this as chains do stretch over time get slack and come of over bumps in the smaller gears on the rear.

a chain guide will also help but wont be much help if the chain is also to slack to start with.

 

[Woosh]

Question ‍ is there a small adjustment to chain tension that can be carried out to rectify this conundrum but which leaves the gear change efficient.

yes, there is. It's a screw to the back of the derailleur with the letter 'B' imprinted near it.
if you tighten it, it will move the derailleur back, loosen it will move the derailleur forward.
You probably will need to turn the B screw half a turn ANTI-CLOCKWISE.
The weakness of derailleur is when it's on the largest cog, if the derailleur is too much forward, it will pinch the chain between the jockey wheel and the cog, the chain becomes noisy.
Too much back, the chain is too loose and may jump.
So you want to move the derailleur forward but stop before the chain becomes noisy on the largest cog (gear 1).

I can take a picture for you tomorrow. I also have a Shimano manual somewhere on my PC at work.

 

[Atlav4]

Thanks woosh and sound wave, will try small increments of the chain tensioner (screw b) anti clockwise probably a quarter turn at a time. Don’t think it needs much, will stick to the road routes as it’s a road bike after all. Thanks again.

 

[vfr400]

Thanks woosh and sound wave, will try small increments of the chain tensioner (screw b) anti clockwise probably a quarter turn at a time. Don’t think it needs much, will stick to the road routes as it’s a road bike after all. Thanks again.

Chain coming off is a problem on all bikes with a single chainwheel and wide cassettes. you can mitigate it a bit by correct adjustment and removing a chain link as it stretches, but you won't eliminate it, as you'll find out. Preventing the chain from coming off with a guide is a much more robust solution.

 

[georgehenry]

You need to do the adjustments mentioned above, and a chain guide will also help, but on a single chain ring set up you could change to a narrow wide chain ring which I have found in the more extreme off road environment, ie mud water, rocks, steps, lots of bouncing around, completely stops your chain coming off the chain ring. Very effective. So much so that it can mask other problems developing but that is another story.

 

[daltonbourne]

Your chain bike fell off can have lots of reasons. A dirty chain may become clogged, leading to losing its grip on the cassette. When this happens, it may lead to the chain slipping on bike. If the chain keeps falling off bike even after cleaning, it may be worn out or damaged. Frequent falling off may also happen when the chain is too long, and this is often the case when the bike is newly fitted. Adjusting the length by removing excess links should address the problem.

 

[daltonbourne]

Your chain bike fell off can have lots of reasons. A dirty chain may become clogged, leading to losing its grip on the cassette. When this happens, it may lead to the chain slipping on bike. If the chain keeps falling off bike even after cleaning, it may be worn out or damaged. Frequent falling off may also happen when the chain is too long, and this is often the case when the bike is newly fitted. Adjusting the length by removing excess links should address the problem.

knowing the reason why the bike chain falling off will help you resolve it easily. When your chain is dirty or clogged, the chain slips off. The solution is to clean the chain with a cleaner and degreaser to clear the links of grime. Worn-out gears can also lead to a situation where the chain keeps coming off bike. This type of wear occurs from long periods of use due to the frequent movement of the chain, especially during shifting and the only solution is to have the cassette replaced.

 

[Andy-Mat]

Lots of good ideas to try, but has anyone mentioned that the chain also needs to be checked for wear damage regularly, as it may now be "longer" than it should be?
Regards
Andy