Technical Chain Question

[weisan]

So I just built up a new bike. Everything is running smooth and shifting crisp except one thing:

Going up a steep slope, under intense pedal pressure, my chain tends to drop off the inner chainring. The rear is at its biggest cog (25).

Everytime that happens, I manage to get off the bike safely (whew!), but I am courting disaster sooner or later.

I double-checked the wire tension, the deraileur's limit stops, no rattling noise whatsoever during spinning, the rear deraileur is tightened pretty good onto the hanger, everything checks out ok. What else am I missing?

Please enlighten.

weisan

[David Kirk]

It sounds like a very worn small ring or a chain line issue.

Dave

[zap]

Chainline

[weisan]

Well, if Master Dave and Master Zap, both concur that the chainline is the problem, who am I to dispute the fact. Although I must admit I did suspect that initially and eyeball the chainline from the back, it looks decent, not perfect. Maybe my eyeball technique is incorrect, and I am looking at the wrong places.

The chainring should be fine because this is an almost new grouppo.

During the buildup, one thing I wasn't sure about is the small little screws that go through the rear dropouts. I screwed them in but I didn't know how much further they should go. It is possible that the left side is not "in line" with the right side by just a tab. When I look at the rear wheel, it seems to be centered between the stays more or less.

So, I guess my followup question would be, what affects the chainline, what are the variables I need to manipulate in order to correct the chainline.

Man, I love wrenching. I love the schooling part, the money saving part notwithstanding. It's all sweat and toil, but I love it! :D

weisan

[Too Tall]

That is a mystery sorta. Do you have an inner chainring installed reversed??? Tell me where the fr. der. inner plate is located relative to the chain...it should rub a tiny bit or VERY little daylight.

[weisan]

Hi Too Tall,

Thanks for responding to my call for S.O.S. I am pretty sure that the chainring is not reversed because the components were transferred directly from my Atlanta three days ago and it was working perfectly over there.

The distance between the inner cage and the chain is "one penny", and nothing more. :D

[eddief]

Have you tried to adjust the front d inner screw until the d will not shift off of the big ring onto the small and then backing out the screw a bit at a time until the d just barely derails the chain onto the small ring?

I just installed a new crank and in the bike stand all worked fine. When I got on the road the chain derailed off of the small ring. I stopped tightened the screw a bit and then no more probs.

Good luck, be patient grasshopper. I never am.

[weisan]

Thanks Eddie,

I will be patient, I promise. :p

Your suggestion is a great idea but I don't think it will solve my problem because it was not about shifting to begin with. The chain is already sitting pretty on the inner chainring before I start the climb. Almost without fail, it will come off near the steepest end of the climb, when the veins in my face and legs are showing... :D

[Kane]

The chain line is most effectively adjusted in the front by the bottom bracket width. You might need to change your bottom bracket.

It is probably a nice day to go to the bike store.

Cheers!

[weisan]

Uh-oh, that's not good.

Yes, I did install the BB myself but I thought it was done right. hmmm...have to look into that....thanks Kane.

[Richard]

That is a cartridge BB, no? Pretty hard to mess up chain line, but possible. I see that you have ultegra 9s, correct? Did the rear have to be spread to accomodate, or was it built with the correct spacing? If it was spread, maybe it was not spread correctly. How does the wheel center in the stays? I hope this is not the case, but something to consider.

[weisan]

Hi Richard,

Yes, it's a sealed Shimano cartridge BB. I don't think I understand what you mean by "spread". The wheel seats center between the stays as far as i can tell.

thanks,
weisan

[eddief]

one other thought about a possible bit of slop in the system?

[weisan]

Hi Eddie,

The thought about having too long a chain came up during my discussion with my friend John. It's possible since I transferred it directly from the other bike without checking. Is there a quick way to verify correct chain length without taking the chain apart and doing that "big chainring to big rear cog, bypass deraileur" exercise?

A bit of slop in the system? maybe...I can't really tell by moving the chain through its revolutions. How much is normal?

[Richard]

My fear was that the spacing in the rear was not originally wide enough for 8-9sd and was "spread"/cold set to accomodate. Depends on when it was constructed. If this was the case, it is possible that it was done unevenly, one side wider than the other. The fact that the wheel sits centered probably indicates that this is moot. Unless you can see the offset, it would be close enough in any case.

You could shift to small/small and verify that the rear derailleur still has some spring tension and that the pulleys are not riding on the cogs. If the chain sags, then there is way too much chain or the derailleur is not tensioning properly.

[weisan]

Thanks Richard and everyone for the overwhelming response. I will verify the things mentioned here first before going further. Hopefully, the problem will be fixed before I bring out the new bike for a long ride over the labor day weekend. ;)

[Richard]

I am not suggesting that you buy these measureing tools, but the site offers insight into issues surrounding chain line and tension:

http://www.parktool.com/repair_help/clg2.shtml

[weisan]

Wow! This is awesome!

I love reading stuff like these. After reading that, I am 95% sure it's the chainline that is causing the problem. I will have to re-check everything tonight.

[eddief]

my recollection is that with Shimano splined bb there is no way to adjust the cups. However, the Octalink xtr bb, one model at least, does come with adjustable cups that I think would make it possible to move the drive side outward a couple of mm.

[weisan]

Thanks Eddie. Yes, it is a Shimano splined bb.

[Luke]

You may need a Dog Fang (Deda) or chain watcher (Third Eye). It is a plastic device that attaches near the bottom of the seat tube to prevent the chain from jumping off the small ring.

[weisan]

Thanks Luke. Nifty stuff :D
I might have to resort to that, if everthing else fails. Besides, it's cheap insurance.

http://www.bikeusa.com/MERCHANT2/merchant.mv?Screen=CTGY&Store_Code=MSGI&Category_Code=ChainDeflectors

[va rider]

hmmmm, doesn't sound like a chain line problem to me. Or at least, not a chain line problem related to the correct bb spindle length.

If you used the bb that worked with the Ultegra crank on your Atlanta, it should be the correct spindle length for the Ultegra crank on your NOS Italian steel bike. If you go to Sheldon Brown's website, you can look up the crankset and find the correct bb spindle length. Then, you need to pull the crank arms and use calipers to measure the spindle length.

But, I doubt it is that, if it worked on your Atlanta it should work on this bike. Why it would derail when the front der. is not even shifting is interesting. I am betting the front der. is not adjust right and when you are climbing hard it rubs and off it falls.

[eddief]

if the chainstays are oriented differently on each bike relative to the bb, then chain line issues could happen. After all, we are talking about mm's here. I was using exactly the same parts on my Rex and my TST and the TST was much more delicate to get it adjusted correctly. I never figured out the exact problem but played with all the variables mentioned and eventually lucked out. With the problem, does it make sense that it would be helpful for the rings to move outward or inward a bit?

[weisan]

First off, let me just say how grateful I am for all the response I am getting from people. Where else on earth, can I have a dozen experts looking over my puny little insignificant chain problem: Serotta Forum!!!! :eek:

varider and eddief, sorry I wasn't clear. I did not use the same BB from the Atlanta. The NOS italian bike uses ...well, an italian thread BB. Frank is kind enough to send one to me together with the bike. Looking at the BB again (I have it with me at work since I rode this morning), it is fully screwed in, no thread whatsoever is exposed on either side.

I did used back the same Ultegra crankset though. Is there a compatibility issue in using a Shimano italian thread BB with the Ultegra crankset?

[zap]

Something else came to mind.

Since it only happens when your going all out, you could be deflecting the frame enough to cause the chain to drop off :rolleyes:

Just kidding. But thats what you can tell your closest friends :banana:

[weisan]

Hey Zap, I am just kidding when I said my veins are bursting out...to be honest, I was anticipating the problem to happen again this morning and so going up that steep hill, I wasn't swinging the bike side to side, in fact, my pedal strokes were so controlled that my rpm is probably not more than 30-35 rpm, and I was looking down occasionally at the chain, hoping I can catch the derail in action. But once I hit the steepest part, and I was looking up, that's when it happens. The timing is just plain sublime. :p

[Birddog]

Check the rear spacing, I believe that was an older frame and it might have been "cold set" improperly ( or not at all) as others have mentioned.

Birddog

[bostondrunk]

Its gotta be a combination of chainline and fd setting.
First, if the front derailleur limit is set right, then the chain shouldn't be able to drop off the small ring no matter what (someone correct me if I am wrong!).

Also, if you put it into the easiest gear, hold up the rear wheel and spin the crank by hand, watching where the chain makes contact with the small ring, does it look like it is 'catching' on the ring before it settles onto it? If yes, then the chainline is probably off, and you need the crankset closer to the BB (shorter spindle).
For the record, I am a horrible mechanic, so all the above may be complete cr#p!! :beer: :banana:

[va rider]

ahhh, the critical missing data.....

I can feel your pain. I have to switch bbs b/c of incorrect spindle length on a early 90s ital. steel frame I just built up with old parts (it came with an old ultegra bb). Yesterday as I was racing up the steepest part of a hill with a buddy, pop goes my chain and down I go. Then, on the next hill I pull the rear wheel out of the drops (another story about an lbs screw up).

Anyway, you need the correct spindle length on the bb for your crankset. Just because the bb and crank are both ultegra or shimano does not mean the spindle length is correct. Also, you really shouldn't mix or match a double crank/bb with a triple crank/bb.

Now, you need to go to Sheldon Brown's website, figure the correct spindle length, pull the crank arms and measure. If it is not correct, you need buy and install the right one.

Good Luck.

[Richard]

With Shimano 9s, it's either double or triple. That determines BB spindle. There are only two choices in length. If the shop delivered a triple bb for a double application, shame on them. There is no need to measure, look at the label on the box. I suppose that it is possible that the bb is not screwed in all the way creating a problem, but Weisan could check that very quickly with a wrench.

BD, the derailleur will not keep it from falling off. It would be beneficial, though to watch the shift and see if the chain tends to ride on top of the teeth at times. I have this (on certain shift combos) occur on bikes where I was too cheap to switch to a 9s front derailleur and use my 8s with a 9s drivetrain (8s cranks 9s rings). Very fine derailleur tuning (reshaping using channel locks) eliminates it for the most part.

FWIW, make sure the chain has no tight links and also make sure that the inner ring did not suffer a bent tooth somewhere along the way.

[weisan]

LOADS of good information here. Thanks guys!!! :D

[weisan]

Hi Pals,

Thought I might update you on the latest about my chain problem. It's fixed as of yesterday afternoon. I went up a hill and the chain popped open. Apparently, one of the links is already loose and on the verge of breaking apart, it causes the chain to flex under pressure and to drop off the ring. So, put it back together, took out an extra link too to get the optimal chain length, no more drop off, perfect!

Thanks again for all your help.

weisan