Chain rubbing on front derailleur

[Holdsworth]

Well after getting my chainset replaced I am finding that when in the high gears on the cassette (6 and 7) and in the big ring, the chain is rubbing on the front derailleur. I have made sure that the derailleur is straight, I have adjusted the cable tension so that is just taught at the loosest setting, the limit screw for the top end is undone by a fair way.

This is a pain because the new chainset has two less teeth on it (LBS had nothing else in) so I need to use the higher gears at the back more often.

All that and it still rubs on the right-hand side of the 'railleur, it just can't move far enough out before the cable goes tight and won't move any more.

Any help is mucho appreciated

 

[screenman]

Can you pull the mech across? if so this would lead me to think cable adjustment, if not are you looking at the correct screw?

 

[Holdsworth]

No the mech cannot be pulled across any further. To my untrained eye, the moving part appears to hit a kind of protrusion in the fixing bracket that stops it moving any further, this protrusion in unmoveable and is fixed to the clamp that goes around the seat tube.

I appears, though I hope not, that the mech does not have enough travel built in to accommodate the new chainset even with the H screw fully slackened off

I know it is the H screw I have been twiddling with as the the other puts a stop to the movement on the way in.

 

[Holdsworth]

I have uploaded two pics to show what I mean.

The first pic shows the protrusion I am talking about, it is the little circular object that is stopping the moving mech.

The second pic shows the limit screws on the older mech, the lower one is the H screw. The lighter coloured component is the part that moves, as it is released by a slack cable (for shifting into the inner ring) it pivots on that screw that lies in front of the spring and the unseen bit of metal beneath hit s the L limit screw on the top.

 

[Andy_R]

check which bottom bracket the new chainset manufacturer recommends; it may be that your old one is a tad too short.

 

[mickle]

check which bottom bracket the new chainset manufacturer recommends; it may be that your old one is a tad too short.

Or, more probably, too long.....

 

[Andy_R]

Or, more probably, too long.....

paint me blue and call me a numpty... i know what i meant...just didn't say it!

 

[Holdsworth]

How would I go about finding out? The chainset if some el cheapo (crap?) one that the LBS buys in from his suppliers, Sunrace or something.

 

[Andy_R]

Sunrace, or Suntour?

http://www.sunrace.com/en/products

http://www.srsuntour...index.php?sid=1

did you change the chainset yourself or did your lbs do it. have a look in your lbs and see if there is an identical one on display for sale, or if you still have the receipt it should have the part listed on it.

 

[RecordAceFromNew]

It sounds like the LBS didn't measure the old chainline, and supplied you with a chainset that does not reproduce it with your (old?) BB, or less probably you replaced a double with a triple which requires more reach the front mech can't provide.

Obviously it depends on whether you asked the LBS to supply you with the right chainset for your bike, or you just asked for a chainset. If the former they should remedy it. If the latter you might have to figure out whether it is best to a) do nothing, b) change the front mech, c) change the chainset, or d) change the BB. Options b, c) and d) will require identification of what components, chainline, chainset to bb clearance etc. you now have, and planning (so as not to run the risk of acquiring another unsuitable component).

It might also be helpful if you still have the old chainset. It would certainly be instructive to know what the chainline used to be compared to what it is.

 

[mickle]

You've bought (or been sold) the wrong chainset. Someone has made a mistake - was it you or the shopkeeper?

 

[Holdsworth]

Well to clarify, the chainset it replaced was a double and I can confirm that yes the new one is too a double. And it is a SunRace one, R90 according to the writing on the crank.

I simply went in there explained my problem and he ordered the chainset that I assume he knew would fit my bike. I have no part in choosing the exact one and he fitted it all for me as well.

I no longer have the old chainset, the LBS removed and I assume he chucked away along with all other worn out parts.

 

[RecordAceFromNew]

According to their latest catalogue (a 2008/9 one looks pretty much the same), Sunrace's R90 series double chainsets come in two main versions, compact 50/34 and normal (53/39 or 52/42), both delivering 43.5mm chainlines with 103mm and 111mm bb respectively. Chance is e.g. you were given the compact? If so the issue is while 43.5mm is the typical road chainline, 103mm bb were rare traditionally - the majority were longer.

As to what to do next, it sounds like the LBS made two omissions, first they did not measure the old chainline and reproduce it with new components, secondly they did not test and cure the problem you are experiencing after the change. I guess you could ask them to fix it, but you should be aware they might charge you for another component which might or might not suits you best (e.g. are you better off having a new bb, or a new front mech, or a different chainset?). They might also try to bend the front mech cage or rotate it to make it work, but that could create new problems.

 

[Holdsworth]

I have booked my bike into the LBS to have it looked at tomorrow, the owner is sure that moving it around would fix but going on the comments above I am not believing it. I have already made sure that it is in line with the chain wheel and it looks to be at the right height. I had a problem this evening coming back home where I couldn't shift back into the big ring after going up a hill in the granny gear. I had to place it on the big ring by hand!

As I have said, the limit screws seem to be set correctly and things cannot move more because of that round protrusion.

I will see what he says tomorrow. I just hope this doesn't cost me dearly

 

[RecordAceFromNew]

If they deny causing the problem the proof of the pudding is the chainline (centre of the bike to half way between the two rings) isn't it? Mismatched chainset/bb can easily make it quite a bit more than typical road spec (which is 43,5mm), and which can cause problems like yours.