Freak mechanical-any ideas?

100Suns

I chalked up a new experience for the mechanical problem list this morning. The chain was on the big ring (probably the second time in months) and dropped on the inside. It happened on the way through a small roundabout at a fair pace while leaning. After a big moment, thinking the chain had broken and I was on the way to the ER/morgue via a faceplant on the asphalt, I managed to dismount in a civilized manner. The dérailleur was still centered over the big ring and the cable was in tact. I can't understand how it managed drop to the inside and more importantly, was it a freak one-off? Any ideas appreciated.

Raam

Rupture in the space-time continuum?

100Suns

Raam wrote: »

Rupture in the space-time continuum?

Too obvious-had discounted that after applying the Heisenberg uncertainty principle which dictates that any solution is mere conjecture.

BTW There's a hot fashion thread running over in social and personal which might be more suited to your skill set:pac:

DirkVoodoo

How are your chainrings looking? Any slight kinks?

100Suns

DirkVoodoo wrote: »

How are your chainrings looking? Any slight kinks?

Thanks DV. Checked at the time and nothing obvious. And the chain and chain rings are clean. It's a mystery Ted.

Raam

Wild guess: you were putting down such awesome power that you flexed the drive train a bit, hit a small bump and there was enough space and force for the chain to slip off.

Captain Havoc

Andy, is that you?

100Suns

Raam wrote: »

Wild guess: you were putting down such awesome power that you flexed the drive train a bit, hit a small bump and there was enough space and force for the chain to slip off.

You're confusing me with Jens again! The second part sounds plausible though.

100Suns

Captain Havoc wrote: »

Andy, is that you?

I ruled out incompetence notwithstanding that it is generally responsible for the majority of my woes.

bcmf

Are you 100% sure the fd was still centered over the Big Ring. If the chain dropped to the small ring while the Fd was on the Big surely the chain would have jammed. Is your Fd now shifting between small and Big without issue.

doozerie

Some things that spring to mind as possible causes:

* the front mech moved. It wouldn't take much movement to dislodge the chain so maybe it looks okay by eye but is actually subtly out of line. If that was the cause then maybe the limiting screw on the derailleur needs adjusting or the cable needs some slack removed. Or maybe the front derailleur cage is not parallel with the chainrings.

* the chain line was at the limit and a slight bump in the road pushed it over the edge. Which sprocket were you in on the back at the time? If you were in the innermost one then maybe the set up on the bike can't properly handle that much cross-chaining. If you were in any other sprocket at the rear though then chainline should not be a contributing factor at all.

* maybe the chain jumped a little on the cassette, even briefly, which might be enough to cause the chain to fall off the front ring too. If that was the cause then you might just need to adjust/tune the rear derailleur, or ensure that the cassette is tightened fully. A tight link in the chain might have the same effect, but again you'd expect that to be noticeable the rest of the time too.

* possibly one or more of the bolts holding your chainrings on are loose, which might result in enough play in the rings to dislodge the chain when you put some pressure on. Play in the bottom bracket is another possibility but that would probably be more noticeable.

* maybe your bike is not UCI approved and Pat McQuaid willed the chain the fall off to teach you a lesson. You'll need a bike exorcism to sort that one out.

'68 Fastback

Did Contador fly past you laughing his way to the GC?

Nothing technical to ad to what the lads have suggested. Does sound abit like a worn ring, how old is your big ring?

100Suns

Thanks Folks

Doozerie may have been on to something. I checked the chain this morning. Although regularly cleaned and lubed, there was a stiff link which wasn't riding properly over the cassette when spun backwards. I also checked the bcd bolts and a couple could have been a little tighter . This could have given enough flex on the ring to throw the chain down the inside of the mech. This morning was incident free so hopefully that's it sorted.

doozerie

A precautionary exorcism is always worth considering too, regardless.

bcmf

Look there is no other solution; you need a new bike.

100Suns

bcmf wrote: »

Look there is no other solution; you need a new bike.

Tell me about it. It's a Cervelo Soloist bought on the basis of Raam's now obvious infatuation.:mad:

Raam

I have an R3. That's "R" followed by "3".

100Suns

Is that the only Cervelo you'll endorse.;)

In fairness, it is a great bike IMO (as is the R3). My problem is entirely attributable to my own negligence.