Bobing Chain

[Chief]

I am running a DA triple and just installed a new chain. Now when I am in the middle chain ring on the road, the portion of the chain on the slack bottom side is bouncing up and down which causes the RD to respond in a jerky manner as it tries to keep a uniform tension. This does not happen in the small and large chain rings nor does it occur in the middle chain ring when the bike is on the stand. I put on a different wheel and the same thing occurs so it is not the cassette. When I rotate the chain backwards with the bike on the stand, the chain operates smoothly so I don't think there is any sticking links. This triple has some 24,000 miles on it. Could the middle chain ring be worn and is causing the problem. If not, any ideas.

[Ken Robb]

you're putting us on, right? 24,000 miles?? How many miles did you ride the chain?

[Chief]

you're putting us on, right? 24,000 miles??

I swear, 24,000 miles is less than 3 years. The chain had about 6,000 miles on it.

[pale scotsman]

Are you sure it's the right length?

[csb]

worn ring
or
bent tooth?

[Ken Robb]

I would think that 24,000 miles is way over average mileage on a chain ring, especially a 39 tooth which would wear faster than 52 or 53. Heck, 6,000 miles on a chain is double what I get too. You must be a smooth rider.

[coylifut]

the fact that this happened after installing a new chain says to me that you have a hooked tooth (or many) on the middle ring. if we were talking about a mtb here, you'd likely experience chain suck as soon as the system got any kind of mud on it. 24,000 miles is the outer limit of the normal life of the ring. take a look at the ring and see if it looks any like this. the old stretched chain had enough slop to compensate, but a new one will catch. make sure to replace your cassete as well our you will quickly wear out your chain which will result in fast wearing rings as wwell.

[Too Tall]

What Coy said. You got your $$'s out of the equipment pal. Time to ante up!

To get better performance out of well worn rings I've used a small mill bastard file to clean up the edges. Coy's cool pic. is great. Look at the ring edge on and you will see a burr that needs to be knocked down with the file. It's an easy job you can do without taking the ring off.

And by the way, you sir are a BEAST :)

[coylifut]

What Coy said. You got your $$'s out of the equipment pal. Time to ante up!

To get better performance out of well worn rings I've used a small mill bastard file to clean up the edges. Coy's cool pic. is great. Look at the ring edge on and you will see a burr that needs to be knocked down with the file. It's an easy job you can do without taking the ring off.

And by the way, you sir are a BEAST :)

Tall one, in my experience, the top quality rings (such as Ultegra) have a low tendency to bur. By the time they do, the teeth are quite hooked. However, I do see mtb rings (they're quite a bit smaller) bur prematurely and can be salvaged with filling.

Cheif. Congratulations on wearing out your drive train. thats hard for us to do here because our weather requires multiple bikes (fender, fixe, race, cross, mtb...) and it takes quite a while to put 24k on any one bike. the R & R is quite easy being that Shimano uses self extracting crank arm bolts.

[Too Tall]

What? are you a mind reader??? Yes, I've only ever had to file off burrs on mtn bike and tandem rings.

[Chief]

My problem with the bobing or bouncing chain was due to a worn chainring after over 24,000 miles. Once the chainring was replaced, there was no more bouncing. The old ring, when compared to the new one, exhibited quite a bit of wear. Efforts to file the burrs off to alleviate the problem was not successful. Seems as though they don't build them like they use to. Here's hoping the new chainring will last more than 24,000. ;) Thanks to all for your valuable advice.