Chain jamming - are cogs too close to chainstay?

[yakheart]

I am having problems with my chain jamming between the front cogs and the chainstay and (twice so far) breaking.

The first time the chain broke I took the bike to my LSB who reckoned that the cogs and chain were not worn. They mentioned that the cogs were quite close to the chainstay, but reckoned that it should be OK.

I had just bought the bike (Dawes Hybrid) from eBay and don't know the history of what may have been changed on the bike, so I put the jamming down to me just not taking care to clean and lube the chain, but after the second break recently, I took a closer look at the cogs.


http://www.panoramio.../photo/49076167

The cogs do look very close to the chain stays, to me, but I really don't know. Here is a link to a picture taken from the underside of the bike with the back of the bike to the right. You can see the marks on the chainstay where the chain has jammed on the smallest cog. You can also see that the small cog is close to the chainstay, but is it unusually close?


If it is closer than it should be, what is the best way to fix it?

 

[Sleeping Menace]

I am having problems with my chain jamming between the front cogs and the chainstay and (twice so far) breaking.

The first time the chain broke I took the bike to my LSB who reckoned that the cogs and chain were not worn. They mentioned that the cogs were quite close to the chainstay, but reckoned that it should be OK.

I had just bought the bike (Dawes Hybrid) from eBay and don't know the history of what may have been changed on the bike, so I put the jamming down to me just not taking care to clean and lube the chain, but after the second break recently, I took a closer look at the cogs.


http://www.panoramio.../photo/49076167

The cogs do look very close to the chain stays, to me, but I really don't know. Here is a link to a picture taken from the underside of the bike with the back of the bike to the right. You can see the marks on the chainstay where the chain has jammed on the smallest cog. You can also see that the small cog is close to the chainstay, but is it unusually close?


If it is closer than it should be, what is the best way to fix it?

I've never seen front rings that close to a frame, but I'd think a simple 2mm bb spacer would give you a bit of room, whilst costing you almost nothing. Also, as mentioned, the proximity to the stays wouldn't be causing the chain to get sucked in there, usually a chain with sticky links, or very badly worn chainrings is the culprit. Give the chain (drivetrain for that matter) a good clean and lube? and follow the other posters link for info to adjust..
........................
http://anotherdoorat...theinternet.org

Cycle related blog entries, including a few 5 minute reviews:
http://anotherdoorat...tegory/cycling/

 

[Zoiders]

There is very good chance that this may be shifting technique related and not set up related.

 

[frank9755]

It is very close, but if the chain didn't come off, it would be ok.

Is the front mech adjusted properly? ie is the lower limit set up so that it doesn't throw your chain too far inwards?

If it is, then make sure you ease off the pedal pressure slightly when changing into the small chainring. Going down to the small ring on a triple always has to be done with care as it is the most likely shift to lead to the chain coming off.

 

[Zoiders]

Spin - Don't grind.

The picture is at a bit of an angle so it's misleading, a hybrid will use a 135mm MTB hub - the chain stays kick out a fair bit more to take the tyre and the hub so the chainrings will indeed look and be closer than they would on some road bikes, the chain line remains the same though as the major difference is the axle and not the hub shell.

 

[yakheart]

Thanks for the quick and useful replies - it all makes sense.

I'll read up from the links, take better care of my bike, spin the cranks and change gently.

Thanks again.

 

[Banjo]

If you can make the chain come off by pushing the derailleur in with your thumb while spinning the pedals then the limit screws need adjusting.

 

[andrew_s]

What causes the chain to get jammed between the chainrings and the chainstay is commonly called chain suck, where the chain doesn't come off the chainring on its way towards the rear mech, but instead carries on round to the chainstay.


Things to look at...

Check chainrings for roughness at the edges of the teeth. Sometimes a bit of grit can get jammed between the chain roller and tooth, and pedalling pressure can cause a bulge in the side of the tooth. New chainrings can also have rough tooth edges.
Very worn chainrings can get hooked teeth that don't release the chain.
Check the rear mech pivots for stickiness.
Check that the chain isn't too long - just long enough to allow you to change to big/big, and no longer.

Hooked teeth and rough edges can be cured with a file.