View Full Version : chainrub problem ?
ClutchCargo
05-15-2008, 09:13 AM
hello, forumites. I hope someone has a solution to my friend's problem (no really, it's not me -- not that it matters, of course) -- when he is in the small chainring and any of the smallest 3 cogs, the chain rubs against the large chainring. this started happening after he installed a new cassette, chain and chainrings (using the same cranks). he changed them because he thought they might be wearing out. the problem did not happen before the changeover. his chainrings, both before and after, are 50/34, and he has the same wheels as before. I believe it's a 9 speed dura ace setup.
of course it's not usually a good idea to cross-chain, but seems like he ought to be able to use the 7th and 8th cogs. besides, he could do that before.
any idea what's going on here? the only thing I have thought of is maybe - accidentally or not - he installed a shorter chain. other than that, we're stumped as to what is causing this and what he needs to do to fix it.
thanks for any help on this!
cheers.
victoryfactory
05-15-2008, 09:31 AM
If the cassette, chain and rings are all the same models as
before, something is no longer lined up. Are you sure the rub is on
the big ring and not the FD cage?
Did he install one of the rings backwards, making the rings closer together?
(If that's even possible considering the counter sunk holes in the chainrings)
VF
If you are sure it is rubing against the big ring and not the deraileur, I'd check the spacing between the chainrings to make sure it is the same as before. Are the rings the same brand, model, etc.?
Kevan
05-15-2008, 10:09 AM
It's hard to believe anyone could screw up the install of new chainrings unless they got the wrong model rings, or mounted them facing the wrong direction. I guess it could happen though and the bolts wouldn't sit right.
The cassette could truly be messed up if a spacer was incorrectly used, not used, or the wrong sized lockring was installed.
Working slow and methodical, it's hard to goof the exchange. Though I never saw that different sized lockring coming...myself.
David Kirk
05-15-2008, 10:18 AM
How long are the chainstays?
dave
ClutchCargo
05-15-2008, 11:35 AM
How long are the chainstays?
dave
it's a stock litespeed tuscany from around 2001 or 2002, I think.
that would make them 40.6, it looks like.
The cassette could truly be messed up if a spacer was incorrectly used, not used, or the wrong sized lockring was installedIMO that's not likely the problem because he reportedly went from being able to use 8 cogs to only 6. That's a lot of difference if everything else was left as before as stated in the OP.
any idea what's going on here?One other thing to check in addition to clearance between chainrings. Is there any chance your friend could have installed a wider chain by mistake?
I'd guess you are looking for very minor interference in the 1 or maybe 2 millimeter range. It doesn't take much at the chainrings to affect a couple of cogs at back.
victoryfactory
05-15-2008, 12:02 PM
Ah, Tuscany
I had a '99
One of my all time favorite frames.
Sold it to a friend, got stolen
shucks
PS: I think the chainstays were 41 on mine
VF
victoryfactory
05-15-2008, 12:05 PM
Is the little peg which prevents the chain from jamming
lined up correctly? It's supposed to be behind the crank.
VF
It's hard to believe anyone could screw up the install of new chainrings unless they got the wrong model rings, or mounted them facing the wrong direction. I guess it could happen though and the bolts wouldn't sit right.
The cassette could truly be messed up if a spacer was incorrectly used, not used, or the wrong sized lockring was installed.
Working slow and methodical, it's hard to goof the exchange. Though I never saw that different sized lockring coming...myself.
Funny thing about the chainrings.. I took my SRAM chainrings off last week to clean them, etc.. (see old posts about noise from chainrings)
I didn't pay close enough attention when I took them off.. at least on these they are quite difficult to tell which side is which (small ring) and there is clearly a rotation the big ring is supposed to be at with respect to the crank..
But in any case everything works fine after it's back together.
Is the little peg which prevents the chain from jamming
lined up correctly? It's supposed to be behind the crank.
VF
As long as it's on the outside it should be fine.. if the rings were put on backwards it might be an issue.
Gothard
05-15-2008, 02:15 PM
when he is in the small chainring and any of the smallest 3 cogs, the chain rubs against the large chainring. this started happening after he installed a new cassette, chain and chainrings (using the same cranks)
-Either the spacing between the rings has changed,
-Or the chain is wider,
-Or the angle is steeper between the front ring and the relevant cogs, i.e. the rings are farther towards the canterline of the bicycle. Is it possible to bring the cranks "higher up" on the BB axle with the setup you have? Square taper cranks will creep up the axle when put back on with more force than previously.
ClutchCargo
05-15-2008, 02:24 PM
-Either the spacing between the rings has changed,
-Or the chain is wider,
-Or the angle is steeper between the front ring and the relevant cogs, i.e. the rings are farther towards the canterline of the bicycle. Is it possible to bring the cranks "higher up" on the BB axle with the setup you have? Square taper cranks will creep up the axle when put back on with more force than previously.
I think he has an octalink or ISIS BB/ crank setup, but I will check.
Thanks everyone all for your input on this !
...snipped....
-Or the angle is steeper between the front ring and the relevant cogs, i.e. the rings are farther towards the canterline of the bicycle. Is it possible to bring the cranks "higher up" on the BB axle with the setup you have? Square taper cranks will creep up the axle when put back on with more force than previously.Obviously it could be a combination of things so he should check everything.
However, for the problem to be due solely to overtightening, the chainrings would have to be moved towards the centerline about the distance of two cogs. Possible but highly unlikely without breaking something.
Hopefully he didn't install a shorter BBKT and forgot to mention it.
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