Crank alignment question

[stackie]

I'm stumped.

Baseline info: Dura Ace 9 sp group.

I was riding home from work today when I noticed a grinding noise coming from my crank. At first, I thought the FD was out of alignment, so I tried trimming it with the STI lever. No improvement. So I look down and it appears as if the inner chainring is bent. It is moving back and forth laterally. The big ring looks fine. I stop and take a look and the inner ring is rubbing on the chainstay.

When I get home, I take the crank off, take the rings off and check them for bends. They both lay flat on the granite counter, so I presume they are not bent. I reinstall rings, being careful to have marks facing out on the outer ring and in on the inner ring. Still rubbing. I checked the crank for BB play. No discernible play.

This bike has never been crashed or treated with other than kid gloves. Those who know me, know that I am not a small guy (6'4" and 195), but the same people know that I am also not that strong. I don't think I could have bent the BB spindle, frame, or crankarm. Of course, I don't have any explanations for this rub.

Does anyone have any suggestions? Am I going to have to admit defeat and go to the LBS (who knows which one is any good) and pray that they can fix this without converting my bike into a suicide machine.

Thanks,

Jon

:crap:

[Richard]

When you say "appears bent," do you mean that it has a warp (or is it woof) in it? A consistent single spot that hits, or does it rub through 360 degrees? Could you have a bent spider (is the big ring completely fine?)? How about a bent tooth? You could try marking the rub spot on the ring and then reinstalling the ring one bolt rotated in either direction and seeing if the rub spot moves with the change. Did you check the BB for damage and finally, is the chainstay bent or broken? I can think of very few other causes, off the top of my head.

[stackie]

The inner ring appears bent when viewed from above when riding the bike, but when place on known flat surface no visibly detectable bend is present. The outer ring appears to be straight when viewed from above.

Your suggestion of bent tooth is a good one. I will check that out when I am home. I'm not sure if there is anything wrong with the BB. It spins smoothly and there is no play in the cranks, so I am at a loss. My next step may be to remove the BB and reinstall, although I'm not optomistic about that solving anything.

I cannot see any bend or crack in the stay, and I cannot imagine that I would be strong enough to cause this sort of damage. The bike has not had any incidents, not even falling over.

Thanks for the advice,

Jon

[terry]

if it wasn't rubing before and is now it may be the BB is unthreading itself. a buddy of mine had the same experience. we noticed that the left side was backing out & the drive side was going in. odd, never saw that b/4 or since, a little blue locktite solved that problem.

[Too Tall]

This has "wierd" fix written alllll over it. Maybe you did not properly torque the crank bolt and your crank is not fully engaged on the axel..thus the wobble. You will need to move the bb outboard first.

[stackie]

Terry,

Your suggestion also crossed my mind, but did not know if that was possible. I am headed out to the garage, right now.

Jon