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10 X 3 Chainline Question

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10 X 3 Chainline Question

Old 08-18-10, 06:56 PM
  #1  
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10 X 3 Chainline Question

I recently inherited a bike with an Ultegra 10 speed triple setup. The bike has XT rear, Ultegra front derailleur, 52/42/30 chainrings, and a 12-25 10 speed cassette. The crank is a FSA Gossamer triple.

When my Father-in Law owned it, he mentioned a few times that he was not happy with the shifting but the shop where he bought it was never able to completely resolve the problem.

Now that I have the bike I am able to more precisely describe the problem - when in the middle chainring, if I shift into the largest or second-largest cog, the chain falls off the middle on to the granny gear in the front.

The chainline looks to be just about perfect, and the crank arms are perfectly centred in the frame.

I have been using the bike to ride to and from work for several months and have gotten used to it, but I would like it to work properly.

Has anyone else ever had a chain chronically falling onto the small ring when using middle-ring and largest/next to largest cogs? I expect some noise at worst in this combo (but I would not find that acceptable either).
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Old 08-18-10, 08:16 PM
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This happens every once in a while, and was far more common in the early days of derailleurs.

Two possibilities come first to my mind.

1- even though the chainline is correct, if the bottom bracket axis isn't perfectly square to it (in this case toed inward), the effective feeding angle of the chain is increased. You can quickly eliminate this using a straightedge laid on a secant across the outer chainring and carrying the line to the cassette. Allow for the offset to the middle chainring and see if it lines up where it should.

2-and this was the common issue in the days of stamped steel chainrings. Shift into the middle ring and innermost sprocket. Look straight down to where the chain is just getting ready to engage. It's kept in line by the inner plates fully engaged on the last tooth, then the point of the upcoming tooth has to slide into the space between the next pair of inner plates, which are slightly offset inboard (sorry about too much detail, but others may also benefit). Now it becomes a question of the width of the bellmouth in the inner plates, versus the position of the point. If it touches the edge of a plate instead of sliding in it's all over.

There are two fixes, either look for a chain with more camber or bellmouth on the inner plates, to act like a funnel and guide the point in. Or do as we did 40m years ago and move the point inward slightly, using a file against the outside of the chainring, and spinning the crank like a lathe. You want to remover from the outside of the tapered zone so the point is inboard a bit more to slide into the chain coming from that side. Take it slow and do it by degrees until the problem is solved. (BTW- if I knew how to upload a sketch I'm sure it would help.
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Old 08-18-10, 08:39 PM
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With the bike on a stand, shift into the middle ring position. Shift the rear to the large cog and check for rubbing and clearance. Now, shift to the small cog in the rear and check again for clearance/rubbing. If there's more clearance on the inner position (middle-large cog) than the outer (middle-small cog), turn the barrel adjuster out, pulling cable until clearance is equal. You should be able to shift the entire cassette with no rubbing on the middle ring...and certainly no dropping. It sounds like simple cable stretch.
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Old 08-19-10, 07:25 AM
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Originally Posted by FBinNY View Post
This happens every once in a while, and was far more common in the early days of derailleurs.

Two possibilities come first to my mind.

1... ...the effective feeding angle of the chain is increased. You can quickly eliminate this using a straightedge laid on a secant across the outer chainring and carrying the line to the cassette. Allow for the offset to the middle chainring and see if it lines up where it should.
This seems like a great way to check if this is the problem, but I will still need a strategy to solve the problem. Also, I installed all my father-in-law's components onto a new frame. I am not sure if this was the same shifting problem he was having, but if it was think it is unlikely that two completely different frames would cause the same misalignment issue. It is caused by the frame, right?

2-and this was the common issue in the days of stamped steel chainrings. Shift into the middle ring and innermost sprocket. Look straight down to where the chain is just getting ready to engage. It's kept in line by the inner plates fully engaged on the last tooth, then the point of the upcoming tooth has to slide into the space between the next pair of inner plates, which are slightly offset inboard (sorry about too much detail, but others may also benefit). Now it becomes a question of the width of the bellmouth in the inner plates, versus the position of the point. If it touches the edge of a plate instead of sliding in it's all over.

There are two fixes, either look for a chain with more camber or bellmouth on the inner plates, to act like a funnel and guide the point in. Or do as we did 40m years ago and move the point inward slightly, using a file against the outside of the chainring, and spinning the crank like a lathe. You want to remover from the outside of the tapered zone so the point is inboard a bit more to slide into the chain coming from that side. Take it slow and do it by degrees until the problem is solved. (BTW- if I knew how to upload a sketch I'm sure it would help.
THis sounds reasonable.

I just remembered reading somewhere that some chains are 'directional.' Could having the chain on backwards/upside-down possibly be causing this?
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Old 08-19-10, 07:29 AM
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Originally Posted by Wordbiker View Post
With the bike on a stand, shift into the middle ring position. Shift the rear to the large cog and check for rubbing and clearance. Now, shift to the small cog in the rear and check again for clearance/rubbing. If there's more clearance on the inner position (middle-large cog) than the outer (middle-small cog), turn the barrel adjuster out, pulling cable until clearance is equal. You should be able to shift the entire cassette with no rubbing on the middle ring...and certainly no dropping. It sounds like simple cable stretch.
Thanks for the reply.
I don't think it is cable tension. WHen in the second-largest cog, I can keep the chain on the middle ring by using the trim on the brifter to hold the derailleur against the chain, but it is noisy and still tries to climb off occaisionally. Cable adjustment will only allow me to get the derailleur to move further toward the large ring, and I can already get it to press against the chain.
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Old 08-19-10, 07:38 AM
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Make sure your crank is on the whole way, check your torque on your crank with a torque wrench. I just installed an omni carbon TI bb that was reported to be a tight fit (ISIS) and it was a very tight fit, so tight I was afraid to keep cranking it on when I was putting the crank on. As a result my chainline was off, and it was causing me the issue of the chain wanting to drop off the inner ring in the front when I would go from the larger in the front WHILE the rear was already in the largest ring (the angle of the chain was such that when the FD tried to push the chain down to the inner ring, it would miss it completely and I'd end up with chainsuck).

I'd think this is most likely your issue. Let us know.

Joe
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Old 08-19-10, 07:39 AM
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The straightedge test is simply a diagnostic aid in determining effective chainline vs. true chainline. It tells you how straight the chain feeds to the chainrings. BTW- if the straightedge gives you a different chainline then measuring from the seattube, it means that either the rear triangle is offset, or the BB shell isn't square.

Regardless of the cause the cure is the same, either a chain with more bellmouth in the inner plates to pick up upcoming teeth at a greater angle, or re-cambering the chainring to move the points inboard, or both. If you have any degree of hand skill you'll find the re-cambering to be a quick, easy and effective fix, but don't get carried away lest pickup form the outer cassette suffers.
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Old 08-19-10, 06:17 PM
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Originally Posted by josephjhaney View Post
Make sure your crank is on the whole way, check your torque on your crank with a torque wrench. I just installed an omni carbon TI bb that was reported to be a tight fit (ISIS) and it was a very tight fit, so tight I was afraid to keep cranking it on when I was putting the crank on. As a result my chainline was off, and it was causing me the issue of the chain wanting to drop off the inner ring in the front when I would go from the larger in the front WHILE the rear was already in the largest ring (the angle of the chain was such that when the FD tried to push the chain down to the inner ring, it would miss it completely and I'd end up with chainsuck).

I'd think this is most likely your issue. Let us know.

Joe
This is related to my first thought, which turned out to not be the problem - the crank is a MegaEXO (or whatever FSA calls their system) where the right side arm is permanently attached to the BB spindle from the factory, and the inside of the arm where it meets the spindle is right against the external BB cup. I thought maybe the whole crank is too far out, but upon inspection, there are no spacers on either side to remove or swap to bring it any closer.

I have yet to
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Old 08-19-10, 06:19 PM
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Thanks for the replies. I have not used a ruler to ensure chainline or chainring angle yet, but when I got out to my bike after work I removed the chin and turned it around in case it is a directional SHimano model. Directional or not, it did not seem to make any difference and the chain still fell onto the granny after a few pedal strokes when in the largest or second largest cog.
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Old 08-19-10, 06:40 PM
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You shouldn't need to rely on the FD cage to keep a chain on, that's just a fast way to saw the cage in half. The middle chainring should be able to retain the chain from coming from any sprocket, otherwise 1x10 setups wouldn't work.

The OP said "the chainline looks to be just about perfect" and later posts imply some doubt on that score. Definitely measure and confirm the chainline before looking farther. If the cranks are too far outboard, or angled out in the back, the chain will come from too much of an angle and run over the side. It can be cured, but make sure there's no easily fixed cause first.

Also if the middle chainring is gated try to notice if the chain always derails at the gate. If so, a non gated chainring might solve the problem, though a gated one should work, or can be made to with some judicious filing.

BTW- if you have another chain handy, check if it has more camber or bellmouth in the inner plates and, if so, see if it does any better. That might be all it wants.
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Old 08-20-10, 07:20 AM
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This may or may not be germaine to the current problem but FSA has a history of producing defective cranks.

A couple of years ago my LBS got a shipment of bikes with OEM FSA cranks and had a huge number of customer complaints about poor shifting. Turns out the cranks were made incorrectly and the supplier replaced them with Shimano equivalents which completely solved the problem.
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Old 08-20-10, 07:37 AM
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Originally Posted by HillRider View Post
This may or may not be germaine to the current problem but FSA has a history of producing defective cranks.

A couple of years ago my LBS got a shipment of bikes with OEM FSA cranks and had a huge number of customer complaints about poor shifting. Turns out the cranks were made incorrectly and the supplier replaced them with Shimano equivalents which completely solved the problem.
I think this may be the answer. I am going to measure the chainline and check the angle this weekend, but I plan to eventually buy a some new longer cranks sooner or later - it will just have to be sooner.

I recall complaints about the chainrings on this brand of bikes (I am usually proud to say I worked for the company), that the cranks were not 9-speed compatible... I think the real issue may have been cheaply made chainrings.

Thanks for all the advice. I will check it out this weekend and post back when/if I resolve the problem.
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Old 08-20-10, 08:02 AM
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Originally Posted by LarDasse74 View Post
I think this may be the answer. I am going to measure the chainline and check the angle this weekend, but I plan to eventually buy a some new longer cranks sooner or later - it will just have to be sooner.
If you end up deciding to replace these cranks rather than fix them, please don't toss them in the scrap bin. I'll gladly send you the postage and some beer money for them.
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