Is this chain suck?
 

So I had an incident a few weeks ago where something funky happened during a shift and I ended up with a version torsion-ed chain link, killing my chain (posted about it, but search ins't on my side right now). I got a new chain, but it would seem that whatever happened then is still happening, possibly more and more.

I'm going to do my best to describe it; I meant to draw a diagram but I'm being lazy:

The chain is on my big ring, doesn't seem to matter which cog I'm on. I downshift to my small ring. The FD takes the chain that's at the top of the ring and moves it to the small ring, as it should. But, starting at what seems to be about 90° cw*from the top-most point on the big ring, the chain stays on the big ring. Since I'm obviously pedaling it starts to move down and back, and eventually I run out of slack as the chain begins to move back up the big ring, and everything locks up.

It's happened maybe 10 times now, and I've been good enough to catch it before actually mashing the chain and bending another one, and I'm doing my best to shift really slowly and softly, but I can't go on like that.

Are these the symptoms of chain suck? Is there a remedy that doesn't involve buying a new chainring?

(Here's a probably terribly unhelpful video of the ring in question http://dl.dropbox.com/u/1400235/chainring.m4v everything looks pretty straight)

Chain suck as i understand it, when i experienced it, is that the chain "snags" on the front chain ring, either ring, and pulls on the rear derallieur, causing noise and jumping of the derailleur. The chain snags on the bottom of the ring, however. not during shifting. it is a symptom of worn front chain rings. doesn't sound like thats what you have. Have not experienced the problem you descrive but if its already cost you one chain,, perhaps a trip to the lbs is in order?

Unfortunately getting to any sort of worthwhile bs for me isn't very l, but I may have to make the trip. I just spent a good 10 minutes trying to get it to happen on a stand and didn't see even a hint of any snagging or sucking. I feel with someone this elusive even if I did bring it in the best they are going to be able to do is say "well if it's happening, you probably need a new ring".

How old is the big chainring? How old is the chain? I'm thinking there's wear on one or both, making it difficult for that last tooth that was on the big ring before you shifted to "give up" the chain and let it onto the smaller ring. If it happens only in one or a few particular crank positions, then I would suspect one or a few problem teeth on the chainring. If it happens "universally" (no matter where the crank is when you shift), then I'd lean toward either general wear on the chainring or the chain. Do you have a chain wear checker?

the chain is like two weeks old, since I had to replace the one that this phenomenon destroyed about a month ago. It has about 300-400km on it. The rings are as old as the bike, which I got in October of 07. I don't ride all that much except during the summer, so total mileage on the bike shouldn't be anywhere close to wearing-through-chainring levels. I'm guessing it's the result of some sort of damage, but nothing's happened to the bike in the last month or so that I can think of and the problem has come seemingly out of the blue.

Did this happen on the old chain?

How often (in km or mi) did you replace the chain previously? If you replace the chain promptly when it reaches its wear limit, the chainrings and cogs last longer. If you let the chain really wear before replacing it, the chainrings probably wore along to match it, and they wouldn't play well with a new chain.

The first time it happened was on the previous chain; the first time it happened was also the end of the line for that chain. It's now happening quite a bit with the new chain, but I obviously can't say for sure if it'd be happening if I still had the old chain. Not sure how worn the old chain was, but I'm generally pretty good at replacing them when they need it. When I did a side-by-side with the brand new chain to get it's length, it honestly didn't seem that stretched or anything. Well, regardless of the cause there's no skirting the fact that it's happening, and I doubt there's much anyone can do to really fix it.

If I were to just replace the big ring, any value in getting one better than what I've got? It's an FSA compact, uh, Omega I think. Not really in the budget right now to get anything spectacular or even a whole new crankset if I can avoid it. Thanks for the help.

There is a video of Test Rider reviewing Rival where he gets chain suck when it is not properly tuned. Here is the link http://testrider.com/fly.aspx?layout...xid=81&cid=105 it is at about 3:10.

thanks for the link. looks like i need to change my chainrings as well

Sounds to me like when you f'ed up your old chain, it did a number on some of your chainring teeth as well. You could technically call what you're experiencing chain suck. I rarely see it on road bikes, but it's common on mountain bikes, especially if the rider fails to clear rocks and hits the chainring on them instead.

So, it looks like you might need a new chainring.

That's why I was wondering if it was happening in one or a few spots, or anywhere on the chainring.

It's hard to tell since a chain will go through more than one tooth during a shift. However, chainsuck due to a damaged chainring will also commonly occur when not shifting, too.

I can't say for sure, but I think it's probably happening in only one spot. It seems like every time it happens and I need to backpedal to correct things my feet are always in the same position. But that's just kind of a gut feeling I get thinking back; like I said, I tried to recreate it on the repair stand for a while and couldn't get it to happen.

"Sounds to me like when you f'ed up your old chain, it did a number on some of your chainring teeth as well." I don't see that being the case, because the only reason anything happened to my old chain is because of this exact phenomenon. Whatever's "sucking" the chain to the ring happened first, then busted the chain. Not saying that didn't make the situation worse, but I don't think it started the problem.

Since this isn't chainsuck in the classical sense, and I'm not seeing any issues with just normal pedaling, anyone have any theories on what the issue is? Just some freak tooth misalignment that only shows up when shifting?

How about your chainring is only slightly f'ed up?

Classic chain suck is where the chain snags on the small ring and feeds itself through the gap between chain ring and chain stay. On most frames that arnt made of steel, tis spells doom for the frame.

Change your chain rings and check the front mech adjustment before you get real chain suck and wish you had got it sorted earlier