Originally Posted by derwagon
I have Ultegra Double crankset. The chain always rubs against the front deraileur. I have adjusted it. I have had two mechs at two diff. shops look at it. No joy. They tell me the derailuer I have is for a triple but the specs say it can be used for double or trip. Any thoughts? The noise and the thought of the bike running inefficiently are bugging me.
You hav to give a bit more info. Does the chain rub during an entire revolution, or only at certain points in the rotation. What is the chainring combo and what is the cassette range (also is it 7-8-9-10 spd)?
The PArk tutorial is a good start point, but each of those adjustments need to be 'customized' in some cases. The new, wider hub/cassette combos can make the adjustment really touchy.
If the bike is 'stock' and comes from a well-known company, is midrange or better, then the componentry is prolly OK as a working combo. If it's other than stock, due to shop customization, either at your behest or some other reason, then the components in question may not be the best working combo for your bike.
If stock, I suggest finding another bike on a showroom floor that is the same model, check compare the adjustments of height, derailleur angle of the showroom bike against yours - try to mimic those settings.
If it rubs on the showroom floor, Oh well...
Derail height - I use 2mm at the point of the outer cage plate that is closest to the chainring, which is a bit diff. from the park instructs. A particular derailleur, put on a particular seat tube (and itz angle) may find the closest point at the rear of the cage, not the front as in the pic. Use the closest point and set that to 2mm.
Angle - depending on chainline, you may have to 'finetune' the angle.
IF THE CHAIN RUBS ONLY DURING PART OF THE REVOLUTION, then check how much variance. If the chainring, in a sighting test looking down at the ring under the FD, 'wobbles' 1 -2 mm, that prolly manufacturing variance. 3 ,4 or more mm and its a defective crank. BB or both. I;d ask to have either/both replaced.
If the chain runs straight and smooth without any pressure on it, but rubs under your pedaling pressure, then itz likely the crank to BB spindle interface OR the BB moving within the retaining cups.
For that reason I really dislike sealed BBs. Give me a good open bearing Campy or other quality BB any time. But you may not have that choice.
Is the crank/BB combo square taper, octalink or ISIS? If Square taper, then take it off and put it on in a different position, that may resolve the wobble. If its Octalinl or ISIS you can try that but less likely to have much affect - with these you;re at the mercy of how closely the tolerances of Male/female splining match from spindle to crankarm.
Check that the cups are snugged well against the BB cartridge. Play of just a tenth of a mm at the cup inteface will translate into 2 -3 mms at the outer edge of the large ring.
You may also be rubbing the chain against the outer ring (while chain is on the small ring) not the FD, check for that condition. I;ve found that my new compact crank, 50-34, rubs the outerring if the chain is on the 34 and I;m trying to go to the smaller rear cogs (higher/taller/larger gear ratio).
With the modern frames I'm hoping that BB flex is not the issue, but if it happens while you're mashing the pedals, then it may be frame flex.
Good luck - I really dislike FD/chainring/chain problems.