Issue with Chain coming off front cog

wannabecraig

I bought a 2nd hand banger for bopping about town. Manged to get it into good condition, replaced a few bits and it's good to go until I turn it into a single speed.
For now it's a 6 speed, one cog on the front. The chain comes off a lot though, mostly when I'm freewheeling and start to cycle again but also when I hit a serious bump.

One thing I notice is that when I'm just wheeling it it doesn't freewheel as such, the peddles rotate, not all the time, but most, so I don't get that clicking noise the back cogs usually make.

Any ideas/thoughts?

Fian

Sounds like the chain is too long for your set up - have you replaced the front ring/chain/cassette/derailleur? Is there more spring left in the rear derailleur or is it fully extended?


Does this problem happen in all gears or only when you are on the smaller rings in the back?


Or perhaps the chain has stretched too much and needs replacing?

steamsey

The cogs at the back don't click - it's the freehub that the cassette sits on that does the clicking. It might need to be cleaned. Easy enough to get cassette off and clean hub - usually but there are all sorts and some are a nightmare to work with. If it's a standard enough Shimano / Sram one - you might be able to get at it and clean it / lube it.

In terms of the chain - as prior poster said - chain might be too long. You can find vids on how to check this but essentially put chain on smallest ring at back, and see how loose / floppy it is. If very much so, might need to remove a link. This may fix your problem.

If above does not solve problem and chain keeps dropping - the next issue is that your front ring is not designed to hold the chain - it was probably part of a double / single set up with a front mech that essentially held the chain onto the ring. The solution is to buy a replacement front ring - a "narrow wide", meaning basically that it's teeth are designed to keep the chain on. They can work really well and a lot of mountain bikes (a lot of bouncing around) use them with no front mech, no chain guide and the chain stays on happily. Main thing when buying a new front ring is to get the right number of teeth so gearing is not messed up and the right BCD - bolt center distance - which may be printed on current ring or you can easily youtube how to measure. Rings will be sold, for example, as 48T (teeth), 110(mm) BCD - these are the 2 main measurements.

wannabecraig

Thanks.

So I checked on the way in this morning, it's normally when I'm in a high gear (smaller cogs) that it happens, but also if I hit a bump.
The two little cogs are the back, I think they're the derailleur are very stiff and kind of kick back when back peddling.

MY feeling was the chain was loose (too long) but also that the freehub is sticking.

The bike is crap in general and was prob put together by a bunch of odd bikes so I think it could also be the front cog being wrong.
Can I just get any new front cog or do I need a special one?

cdaly_

A sticky freehub/wheel will mean that the chain goes slack when you freewheel and is then loose when you start pedalling and so will come off easily. First thing lubricate the freewheel/hub and see how it goes. The pedals should not rotate when you wheel the bike along.

wannabecraig

cdaly_ wrote: »

A sticky freehub/wheel will mean that the chain goes slack when you freewheel and is then loose when you start pedalling and so will come off easily. First thing lubricate the freewheel/hub and see how it goes. The pedals should not rotate when you wheel the bike along.

Yes, I'll give this a go. Thanks


On another note, I'm thinking of making it a single speed, not a fixie, any crankset/back cogs combo I should be looking at. Nothing flash as it's just a city bike.

ED E

A SS would ideally have vertical dropouts, got em?

Wishbone Ash

wannabecraig wrote: »

... I'm thinking of making it a single speed, not a fixie, any crankset/back cogs combo I should be looking at....

How many teeth on the front ring? If your on relatively flat terrain, a 3:1 ratio would probably be suitable e.g. 48 upfront with a 16 on the rear. If your front is a 50, perhaps a 17 on the rear etc.

wannabecraig

ED E wrote:

A SS would ideally have vertical dropouts, got em?

ED E wrote:

A SS would ideally have vertical dropouts, got em?

I don't know but I can take a photo when I get home and post

wannabecraig

Wishbone Ash wrote:

How many teeth on the front ring? If your on relatively flat terrain, a 3:1 ratio would probably be suitable e.g. 48 upfront with a 16 on the rear. If your front is a 50, perhaps a 17 on the rear etc.

I don't know, do I count the teeth? Is biggish.

Type 17

The freewheel is sticky (typical on an older bike when the lubricant inside disappears or gets thicker - lubricate it and it should be better. Same for the two jockey wheel of the derailleur.

If there is only one chainwheel at the front of a derailleur setup, and it doesn't have any guide-rings (plastic rings to keep the chain on), it will derail on big bumps or when changing gear on smaller bumps - I had this issue with my own town-bike. In the end, I fitted an old front derailleur (with no cable or shifter) and positioned it correctly over the chain using its lower limit screw - chain never came off again.

wannabecraig

Yeah, it's defo the freewheel thing, I lubed it this morning and now rolls freely.

There is no chain guide so I fear it may still come loose over bumps, have yet to try this out so dont know.
I can get a chain guide to stop this but I'll see if the current setup works first.

wannabecraig

So, after oiling yesterday and the freewheel working there were no issues cycling home yesterday or in today.

As to weather I have the correct dropouts for my single speed dream, perhaps somebody can tell me.