Chain Rub when on Large ring and highest gear

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Aerozine50
Posts: 71
Joined: Wed Aug 03, 2011 08:35 am

Chain Rub when on Large ring and highest gear

Postby Aerozine50 » Wed Jul 18, 2012 08:36 am

Dear All

Many thanks in advance for any advice given on here.

I went and bought a fleabay Specialized Roubaix 07, around a month ago. Lovely bike, and then took it to my LBS for a full change of the Drive Train componentry.

It is equipped with
Dura Ace Rear cassette and shifter,
Front chainrings are a carbon FSA crank and the usual double setup with Ultegra, (Low, Low Trim, High Trim, High).

It has always had a minor issue that is still bugging me in that the High/High gears cause the chain to rub against the cage outer when under load. I've had several goes at rejigging the transmission using the shimano techdocs and always get the same result - (A partial rub against the cage with the bike at speed, and my right leg at bottom dead centre).

Now I do notice that the front chainring moves in and out slightly as the crank goes round. Could this be a case of the Bottom bracket is worn and they (The LBS) should have replaced it rather than simply regreasing it? I.e. bearing play thus the grinding noise at a certain sector in the crank movement.

Anybody have any ideas please? Yes I have been moving the barrell adjuster to see if I can get more tension to shift the cage further over, but this always results in loss of the High Trim eventually.

best regards

Aerozine50
"Commuterised" Specialized Rockhopper Disc 2004.
FCN #7 - Skinny tyres and Cleats.
1962 Rory O'Brien Roadie Lightweight. (but heavy by todays standards!)
FCN #4
2007 Specialized Roubaix Expert.
FCN # 1/2 - Cobbly racing tyres and MTB cleats.

styxd
Posts: 3113
Joined: Fri Oct 29, 2004 00:57 am

Re: Chain Rub when on Large ring and highest gear

Postby styxd » Wed Jul 18, 2012 08:38 am

Have you tried adjusting the limit screws on the front mech>?

Aerozine50
Posts: 71
Joined: Wed Aug 03, 2011 08:35 am

Re: Chain Rub when on Large ring and highest gear

Postby Aerozine50 » Wed Jul 18, 2012 08:54 am

Hi styxd

Yes I have, if I open the limit screws any further on the high side I get "fallout" on the crank side.

Aerozine50
"Commuterised" Specialized Rockhopper Disc 2004.
FCN #7 - Skinny tyres and Cleats.
1962 Rory O'Brien Roadie Lightweight. (but heavy by todays standards!)
FCN #4
2007 Specialized Roubaix Expert.
FCN # 1/2 - Cobbly racing tyres and MTB cleats.

styxd
Posts: 3113
Joined: Fri Oct 29, 2004 00:57 am

Re: Chain Rub when on Large ring and highest gear

Postby styxd » Wed Jul 18, 2012 09:16 am

Well, the fact the crank is wobbling definitely isnt going to help things.

What front mech is it? I had this problem with a SRAM one, no matter how I set it up it would be shite! Swapped to a shimano and its been fine ever since.

Aerozine50
Posts: 71
Joined: Wed Aug 03, 2011 08:35 am

Re: Chain Rub when on Large ring and highest gear

Postby Aerozine50 » Wed Jul 18, 2012 09:36 am

So with that in mind, can anyone tell me what causes a crank wobble then?

Is it a knackered Bottom bracket bearing?
"Commuterised" Specialized Rockhopper Disc 2004.
FCN #7 - Skinny tyres and Cleats.
1962 Rory O'Brien Roadie Lightweight. (but heavy by todays standards!)
FCN #4
2007 Specialized Roubaix Expert.
FCN # 1/2 - Cobbly racing tyres and MTB cleats.

styxd
Posts: 3113
Joined: Fri Oct 29, 2004 00:57 am

Re: Chain Rub when on Large ring and highest gear

Postby styxd » Wed Jul 18, 2012 09:38 am

Turn your bike upside down, grab both crank arms and see if you can rock them side to side/up down/in any direction. If so, your bearings are fooked.

Aerozine50
Posts: 71
Joined: Wed Aug 03, 2011 08:35 am

Re: Chain Rub when on Large ring and highest gear

Postby Aerozine50 » Wed Jul 18, 2012 09:58 am

Will do, so it is sounding like this is the issue, a concentricity problem causing the Large chainring to rub the outer cage when under high load. It doesn't do it when under normal load, but I want this bike to be perfect.

Thanks

Aerozine50
"Commuterised" Specialized Rockhopper Disc 2004.
FCN #7 - Skinny tyres and Cleats.
1962 Rory O'Brien Roadie Lightweight. (but heavy by todays standards!)
FCN #4
2007 Specialized Roubaix Expert.
FCN # 1/2 - Cobbly racing tyres and MTB cleats.

DesWeller
Posts: 5233
Joined: Mon May 05, 2008 15:36 pm

Re: Chain Rub when on Large ring and highest gear

Postby DesWeller » Wed Jul 18, 2012 22:23 pm

Is the chainring bent?

Aerozine50
Posts: 71
Joined: Wed Aug 03, 2011 08:35 am

Re: Chain Rub when on Large ring and highest gear

Postby Aerozine50 » Thu Jul 19, 2012 13:23 pm

Hi Des

I sure bl00dy well hope not sir :cry: , the kit they have put onto the bike is brand new,......

Unless of course the carbon crank itself could be bent? But I doubt it.

Regards

Aerozine50
"Commuterised" Specialized Rockhopper Disc 2004.
FCN #7 - Skinny tyres and Cleats.
1962 Rory O'Brien Roadie Lightweight. (but heavy by todays standards!)
FCN #4
2007 Specialized Roubaix Expert.
FCN # 1/2 - Cobbly racing tyres and MTB cleats.

veryslowtwitch
Posts: 176
Joined: Mon Jan 30, 2006 22:02 pm
Contact:

Re: Chain Rub when on Large ring and highest gear

Postby veryslowtwitch » Thu Jul 26, 2012 10:35 am

The big chainring could be out of true even if new. Take it off and lie it on a flat surface. It should lie flush.

If the ring is ok then back to the BB and spider.

Regards

Alan


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