Chainline issue

[Spoked Wheels]

I'm trying to fix a problem with the chainline.

The symptom is chain noise coming from the big chainring when on the highest gears on the cassette. The shifting is fine, just the annoying noise is the issue.

Sheldon Brown says the chain line for a double is 43.5mm from the midpoint between the two chainrings and the midpoint of the seattube width. Or 46mm from the large chainring and and the midpoint of the seattube width.

I removed the crankset (105), BB and refitted after a good clean.

Measured several times and I make it 45.68mm, so 2.18 over what it should be, not enough to crate other issues.

I measured the BB shell and it's 68.82mm so nearly 1mm what it should be, if the frame is symmetrical then the contribution to that 2.18mm would be less than half a millimetre.

If the problem was the opposite the a spacer could help but not in this case.....

Does anybody know if there is a way around this issue?

 

[Spoked Wheels]

Does anybody know if there is a way around this issue or should I try another forum?

 

[RecordAceFromNew]

Chainline somewhat greater than standard is going to help rather than worsen the large front small back gear. It is therefore unlikely to be the cause of excessive noise, assuming nothing is rubbing the front mech.

Can you detect where the noise is coming from? If the small sprocket is 11T e.g. it is likely to be a little noisier than larger ones - small sprockets are less "round" with a 1/2" pitch chain, and give rise to more vibration. But noise can have numerous sources.

 

[ayceejay]

First check the hanger - is it bent or loose?

 

[Smurfy]

I'm trying to fix a problem with the chainline.

The symptom is chain noise coming from the big chainring when on the highest gears on the cassette. The shifting is fine, just the annoying noise is the issue.

Sheldon Brown says the chain line for a double is 43.5mm from the midpoint between the two chainrings and the midpoint of the seattube width. Or 46mm from the large chainring and and the midpoint of the seattube width.

I removed the crankset (105), BB and refitted after a good clean.

Measured several times and I make it 45.68mm, so 2.18 over what it should be, not enough to crate other issues.

I measured the BB shell and it's 68.82mm so nearly 1mm what it should be, if the frame is symmetrical then the contribution to that 2.18mm would be less than half a millimetre.

If the problem was the opposite the a spacer could help but not in this case.....

Does anybody know if there is a way around this issue?

A midpoint measurement doesn't tell you much if the chainring spacing is out of spec. For that reason I'd prefer to see measurements from centre of each chainring to centre of seat tube.

 

[Spoked Wheels]

A midpoint measurement doesn't tell you much if the chainring spacing is out of spec. For that reason I'd prefer to see measurements from centre of each chainring to centre of seat tube.

I was just following Sheldon Brown standards.... but centre of large chainring to centre of seat tube is 46.4mm I didn't measure to the small chainring as I don't think I have an issue with it.

Chainline somewhat greater than standard is going to help rather than worsen the large front small back gear. It is therefore unlikely to be the cause of excessive noise, assuming nothing is rubbing the front mech.

Can you detect where the noise is coming from? If the small sprocket is 11T e.g. it is likely to be a little noisier than larger ones - small sprockets are less "round" with a 1/2" pitch chain, and give rise to more vibration. But noise can have numerous sources.

I agree with your statement "Chainline somewhat greater than standard is going to help rather than worsen the large front small back gear" but I can hear the noise from about the 7th sproke down to the 11T sproke.

I detect the noise coming from the front of the big chainring. You are right on the 11T being the nosiest. There's no rubbing at all on the dérailleur. Maybe I should try another chain.

Thank you both.

 

[Spoked Wheels]

First check the hanger - is it bent or loose?

Mmmm I never thought of that but it doesn't appear to be bent and the gear changing is crisp, no issues at all. I guess I'd need a tool to check hanger, would I?

 

[ayceejay]

Mmmm I never thought of that but it doesn't appear to be bent and the gear changing is crisp, no issues at all. I guess I'd need a tool to check hanger, would I?

It is an expensive but useful tool. I once had a similar problem to yours and was all set to buy the tool or a new hanger when I discovered that the two little screws holding the hanger to the frame was loose.
I just re-read your OP, did you have this problem before you removed the crankset (105), BB and refitted after a good clean ? If not I suspect a missing/extra spacer the 105 comes with a few spacers when new but they are not always needed.

 

[Spoked Wheels]

It is an expensive but useful tool. I once had a similar problem to yours and was all set to buy the tool or a new hanger when I discovered that the two little screws holding the hanger to the frame was loose.
I just re-read your OP, did you have this problem before you removed the crankset (105), BB and refitted after a good clean ? If not I suspect a missing/extra spacer the 105 comes with a few spacers when new but they are not always needed.

Yes, I thought if I reinstalled everything and measured again I would find the problem was in the initial installation but sadly, it made no difference.

I guess I could take the bike to my LBS and ask them to check the hanger. Even if that needed a little correction, the fact remains the chain line is out by 2+ mm

Are all BB for Hallowtech the same thickness? I guess if I could find that was just a little thinner then I could solve the problem.

 

[ayceejay]

I do know that the crank axle is a tight fit I don't know about various thicknesses though. I have a 105 crankset through a Dura Ace BB that works fine but you do need to re tighten the bolts that attach to non drive arm after a while.

 

[User6179]

Is your cassette lock ring tight enough? , had a rumbling coming from the bike other day but only on the 3 or 4 smallest cogs over rough bits of road , turns out the lock ring had came loose on the cassette .
The bigger cogs are joined together but the smaller ones are individual so only made the noise in the smaller cogs , had checked it on the bike but they did not feel loose , after another few rides with the noise getting worse I checked again and it was loose .

 

[ayceejay]

Incidentally having the LBS check your anger is an excellent idea

 

[Smurfy]

I was just following Sheldon Brown standards.... but centre of large chainring to centre of seat tube is 46.4mm I didn't measure to the small chainring as I don't think I have an issue with it.

The measurement you've just made is probably more accurate than your first measurement, as it is not easy to measure to the centre of a gap.

If it is only out by 0.4mm (46mm versus 46.4 mm), I doubt that is the problem area.

Are you sure the chain is not rubbing on the front derailleur cage? If yes could you use the trim function on the front derailleur shifter?

 

[Spoked Wheels]

The measurement you've just made is probably more accurate than your first measurement, as it is not easy to measure to the centre of a gap.

If it is only out by 0.4mm (46mm versus 46.4 mm), I doubt that is the problem area.

Are you sure the chain is not rubbing on the front derailleur cage? If yes could you use the trim function on the front derailleur shifter?

Sorry my mistake.... I meant to say 48.4mm

There's no chain rubbing... only when cross chain but that is normal and you can tell the difference in sound right away.

 

[Spoked Wheels]

Is your cassette lock ring tight enough? , had a rumbling coming from the bike other day but only on the 3 or 4 smallest cogs over rough bits of road , turns out the lock ring had came loose on the cassette .
The bigger cogs are joined together but the smaller ones are individual so only made the noise in the smaller cogs , had checked it on the bike but they did not feel loose , after another few rides with the noise getting worse I checked again and it was loose .

I haven't checked that in a while. I also find the smallest sprokets they are a little loose but that is normal I think.... even when the lock ring is newly tightened you can feel the 3 smallest cogs are a little loose.

I'll check... thanks